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level: Level 1

Questions and Answers List

level questions: Level 1

QuestionAnswer
what is cell theory?cell theory is that the cell is the structural unit of life that contains metabolic and genetic elements. cells can only arise by division of a preexisting cell. Modern cell theory is that energy flow occurs in cell, heredity information is passed from cell to cell and that all cell have the same basic chemical composition.
what are the two major cell types and what makes them differentProkaryotes have circular DNA free in the cytoplasm, Eukaryotes have a 'true nucleus' linear DNA molecules held in a membrane bound nucleus, contain subcellular organelles to compartmentalise
subdivisions of prokaryotes?Bacteria and eubacteria
where is dna located in prokaryotic cells, and how its structuredNucleoid - not membrane bound, formed into a single loop and does not have introns, genes are grouped into operons
describe the plasmid in a prokaryotesmall loops of non essential DNA and is smaller than genomic DNA. passes vertically during cell division or horizontally by bacterial conjugation. natural plasmids may carry antibiotic resistant genes. easil manipulated in vitro.
describe the difference between vertical and horizontal transmission of plasmidvertical transmission is when a bacteria goes through binary fission (asexual reproduction), horizontal transmission involves conjugation.
what is conjugation?once replication of the plasmid is completed a donor will produce a pilus which makes contact with the recipient bacterium. pore in the membrane if formed to create a continuous conjugation tube. replic plasmid becomes linear and travels to the recipient where it becomes circular.
Ribosomes in prokaryotesfree in cytoplasm (not attached to membrane), composed of protein and rRNA and function to translate mRNA to protein, sedimentation 70s.
Storage granules in prokaryotesstore of carbon, either store glycogen or poly-ß-hydroxybutyrate but not both. Glycogen granules dispersed through cytoplasm visible when stained, poly-ß-hydroxybutyrate stains with the fat stain Sudan black
what are mesosomes?aggregates of tubular membrane structures, derived directly from plasma membrane
what are the internal membranes in prokaryoteslamellae, vescles or tubules, appearance in EM depends on bacteria type
what are bacterial microcompartments?protein shells filled with enzymes for key activities,carboxysomes help autotrophic prokaryotes fix carbon via calvin cycle, pdu are involved in propanediol utilisation
plasma membrane in prokaryotesphospholipid bilayer embedded with proteins, do not have cholesterol which are replaced by hopanoids,stabalising membrane
plasma membrane functioncontains cytoplasm and regulates movement of materials, site of cell wall synthesis, no mitochondria enzymes for energy gen need to be organised within plasma membrane
outer membrane functiongram neg, protects invading bacteria from host defence, essential nutrients pass via porins
function of bacterial cell wall in prokaryotesresists internal osmotic pressure, prevents bursting in hypotonic media
what is in the cell wallpeptidoglycan, strength is due to cross linking of peptide chains, prevents sugar units of polymer sliding over.
capsule in prokaryotelayer of polysaccharide and glycoprotein surrounding the bacteria
what is the periplasmthe space between peptidoglycan layer and the plasma membrane, filled with loose peptidoglycan network and enzymes for nutrient acquisition.
flagellum in prokaryotescomposed of flagellin low amounts of sulphur containing aromatic amino acids and high levels of aspartic and glutamic acid
what colour do gram negative and gram positive bacteriagram positive bacteria are purple, gram negative are pink what colour do gram negative and gram positive bacteria
what is the structure of peptidoglycanhomogeneous
teichoic acidglycerol ribitol or manitol polymers in gram positive cell walls
describe the gram negative cell wallthin layer of peptidoglycan,overlaid by a lipid layer similar to plasma membrane
microbial diversityconsiders the vast array of microorganisms
what are acidophilesbacteria that can grow at a pH of 3 or below, they need to maintain a net outflow of protons to maintain the internal pH
what can acidophiles be used for commerciallycan be used to leach metals from low grade ores
what are alkalophilesbacteria that are inhibited by pH 8-9 or above, must maintain a net inflow of protons to preserve internal pH, example is Vibrio cholerae
what are the three groups of oxygen requirements for bacteriaaerobes - depend on molecular oxygen facultative anaerobes - use oxygen if available anaerobes - cannot use oxygen
Aerobic bacteriafound in terrestrial and aquatic habitats, don't grow in static liquid culture, require shaking
facultative anaerobescommonly used andmedically significant E.coli, require fermentable sugars
Anaerobic bacteriasome killed by oxygen (obligate),others are tolerant, depends on superoxide dismutase
what is the importance of superoxide dismutasedestroys toxic superoxide radicals dormed during oxidation, converts superoxide radical to hydrogen peroxide and oxygen
Temperature - Psychrophilesgrow well at 0 optimum near 15, found in arctic, membranes are high in unsaturated fatty acids
Psychotrophsgrow at 0 but optimum is between 20-30, present in soil, cause of food spoilage
mesophilesgrowth optimum around 20-40, majority are mesophiles, includes bacteria that live in association with or cause disease in animals
Thermophilesoptimum about 55-65, grow in compost, enzymes and nucleic acids are heat stable, membrane lipids more saturated than mesophiles
Hyperthermophilesgrow above 90, optimum between 80-113, includes species which grow in hot areas of ocean
Black smoker' bacteriagrow in sulphide chimneys, grow at 113 '
Halophilescan tolerate high salt levels can colonise saline lakes, cell wall may be damaged from low salt concentrations
are eukaryotes unicellular or multicellularEukaryotes can be both unicellular and multicellular
DNA molecules in Eukaryoteshave linear DNA molecules packaged as chromosomes enclosed in nucleus, have membrane bound organelles
unicellular eukaryotesmost complex eukaryotes, perform all functions, unicellular when food available, when food is scarce they aggregate and specialise to form primitive multicellular organism
what are Eukarytotic cell membranes composed ofphospholipids and protein, spontaneously assemble to form closed bilayers
Eukarytoic cell membranes: two facesThe two faces of the cell membrane are asymmetric in terms of lipid and protein composition Cytosolic face is the inner part, exoplasmic face is the outer part.
Functions of plasma membranesregulation of transport balance of chemical conditions chemical reaction site detects signals interacts with other cells/extracellular (multicellular)
Name the organelles of the eukaryotic cellNucleus, ER, golgi complex, mitochondria, lysosomes (ac), peroxisomes, cytosol, cytoskeleton
Nucleuscontents are in contact with cytoplasm via nuclear pores which pass through both membranes Large dense region= Nucleolus, rich in protein and RNA
What does the nucleus separateseparates DNA from the cytosol; transcription from translation
ER- two types and what they doExtensive membrane structure forming interconnected sacs and tubules Rough ER= ribosomes attached to surface, plays role in synthesis of membrane-bound and secreted proteins Smooth ER = no ribosomes, plays role in producing lipids
ERlipid synthesis, membrane protein synthesis, Ca 2+ ion storage, detoxification Key features: interconnected closed membrane tubules and vesicles
Ribosomesmulti-subunit structures, 50% protein, 50% ribosomal RNA rRNA key to structure and function of ribosomes synthesis of proteins 40s and 60s subunit= 80s
MitochondriaContains DNA and ribosomes, can direct production of some of own proteins self replicating = binary fission site of ATP production, aerobic metabolism, important role in apoptosis Key features: outer membrane intermembrane space inner membrane matrix
what is apoptosis?programmed cell death
Mitochondrial DNAGenes exhibit cytoplasmic inheritance and encode rRNAs, tRNAs, mitochondrial proteins size and coding capacity of mtDNA varies products of mitochondrial genes are not exported mutations cause genetic diseases, leigh syndrome, optic neuropathy
Golgi complexstack of flattened membranous sacs vary in number sacs form from parts of rough ER which break off and fuse Inner face is close to the nucleus ensures that vesicles budding off outer face can fuse with plasma membrane packages lysosomal proteins and proteins to be secreted from cell
Lysosomessingle membrane-bound organelles containing hydrolytic = degrade materials taken up by endocytosis and cell debris degrade damaged newly synthesised proteins
peroxisomessingle membrane-bound organelles contain catalase and urate ocidase = breaks down very long chain fatty acids via beta oxidation oxidation of toxins
cytosolenclosed by the plasma membrane not static contents continuously moving key features: cytoskeleton polyribosomes metabolic enzymes
cytoskeletonlattice like array of filaments and fine tubules involved in cell movement, division, maintenance, trafficking organelles 3 major components: microfilaments = actin microtubules intermediate filaments
microfilamentsF-actin filaments are double helices of polymerised G-actin subunits fibres expand and contract by further polymerisation and depolymerisation, ATP dependent Interact with other filaments and 'motor' to create movement,contraction can cause shape change
actin and myosin in Eukaryotic cellsActin microfilaments work with myosin in muscle fibres myosin filaments walk along the tethered actin, pulling the filaments towards the centre to cause muscle contraction
microtubulesMicrotubules are polymers of tubulin that form part of the cytoskeleton tubes of tubulin: grow by polymerisation from specific microtubule organising centres microtubules can form trackways in cellsalong which motor proteins (kinesins) drag vescles, organelles. Play a fundamental role in partitioning of chromatids in cell divisions
microtubules role in cell divisionpartitioning of chromatids chromatids are one of two strands of a newly copied chromatid, two joined together at centrimere they are called sister chromatids and are genetically identical
intermediate filamentsdifferent types that differ in composition and function, may have role in maintaining cell shape, tissue integrity
what are the specialised features of plant cells?chloraplasts, vacuoles and specialised peroxisomes plant cells have a rigid cell wall can communicate with eachother
vacuolesmake up 80% of plant cell store water, ions, nutrients, degrade macromolecules inflow of water by osmosis causes vacuole expansion and maintenance of turgor pressure expansion of vacuole involved in cell elongation
Chloraplastsdouble membrane bound, contain their own DNA Thylakoid membranes, fused into stacks in places, contains chlorophyll photosynthetic plant cells, contain chloraphyll to absorb light and generate NADPH and ATP
specialised peroxisomesfound in leaves involved in photorespiration (oxygen to carbon dioxide) Glyoxysomes found in germinating seeds, carry out glyoxylate cycle to convert fatty acids into sugars
plant cell wallrigid cell wall comprised mainly of cellulose cross linked by hemicellulose, pectin, and lignin
Plasmodesmatadirectly connect the cytosol of adjacent cells in higher plants
name the different tissues that cells that are organised intoepithelia, nervous tissue, connective tissue, muscle, blood
what is the process of cells going to tissuesDifferentation
why are the layers of the early embryo important?They give rise to the cell types, goes from xygote to blastocyst and then gastrula Germ cells = sperm or egg endoderm (internal) layer = lung alveoli, thyroid, pancreatic cell Mesoderm (middle) layer = cardiac muscle, skeletal muscle, tubule cell of kidney, RBC, smooth muscle. Ectoderm (External layer) = epidermis skin cells, neuron, pigmant cell.
cells produced at 50-cell stage?cells that are produced at the 50- cell stage are called Embryonic stem cells, these cells are totipotent except foetal membranes)
what is totipotent?ability of a single cell to divide and produce all of the differentiated cells in an organism.
what is a pluripotent stem cell?A pluripotent stem cells give rise to cells to a particular tissue
what is a monopotent stem cellsmonopotent stem cells can produce only one cell type
can adult cells be reprogrammed?Adult cells can be reprogrammed by manipulating the expression of key regulatory genes to produced induced PS cells, derived from blood or skin cells.
differentiated cellsdifferentiated cells express different subsets of genes: transcribed genes (transcriptome), and translated proteins (proteome).
Mechanism and Differentiationtissue specific gene expression is primarily regulated at the level of transcription, fine tuning at post-transcriptional and post-translation levels also occur. Signals received by the cell activate transcription factors to turn on certain genes. Inactive genes are characterised by methylation at CG doublets in their promoters
what are the four major classes of cell surface receptorsG-protein couples receptors Tyrosine kinase-linked receptors Ion channels receptors receptors with intrinsic enzymatic activity Singles generated at the plasma membrane are transduced to the nucleus via a complex series of secondary events
Name the secondary events in transducing signals from the plasma membranebinding of the second messengers to receptors and phosphylation
Apoptosis rolehas roles in embryogenesis, tissue homeostasis, damage limitation, control and functioning of immune system. Evolutionarily conserved and genetically controlled
what are the Two main gene families involved in apoptosisBcl-2 family (regulation) Caspase family (execution) Many accessory proteins - death domain proteins
characteristics of apoptosisMild convolution, chromatin compaction, margination condensation of cytoplasm Breakup of nuclear envelope, nuclear fragmentation, Blebbing cell fragmentation Phagocytosis
Importance of ApoptosisToo little apoptosis can lead to cancer, autoimmune diseases and prolonged viral infection Too much apoptosis leads to neurodegenerative diseases, autoimmune, tissue damage through trauma, progression of AIDS.
how does apoptosis become unregulated?Genes controlling it become damaged or aberrantly expressed, inappropriate triggering of apoptosis, the interference by exogenous genes
name cell types: EpitheliaEpithelial cells - from sheets that cover the inner and outer of the bodies surfaces Absorptive cells - have microvilli to increase their surface area ciliated cells - have cilia that beat to move substances over the sheet Secretory cells - secrete substances out onto the sheet
What are the main types of intestinal cellsAbsorptive cells outnumbers others 10:1 Goblet cells: secrete mucous Paneth cells: secrete growth factors and antibacterial substances Enteroendocrine cells: secrete peptide hormones and serotonin into gut wall
Name 3 Neuron cell typesNeurons are specialised for communication, the axon conducts electric signals away from the cell body multipolar interneurons motor neurons sensory neurons
Cell types: rod cells, what are they?Rod cells are specialised sensory cells in the retina, layers of disks contain light sensitive pigmant = rhodopsin Light evokes an electrical signal that is transmitted to the brain
Cell type: Erythrocytes, what are they?highly specialised, carry oxygen, protein component is haemoglobin loss of nuclei and internal membrane, cant replicate
Connective tissue, name some different connect tissues that arise from fibroblastsfills spaces between epithelial sheets and tubes Bone cell - osteoblasts/osteocytes Fat cells - adipocyte smooth muscle cell Cartilage cell - chondrocyte
what does fibroblast differentiation depend onDepends on the etracellular matrix YAP and TAZ are transcription regulators that move to the nucleus in response to tension developed in the actin-myosin bundles in the cytoplasm
What does the transcription regulators YAP and TAZ stand forYAP = yes associated protein TAZ = transcriptional coactivator with PDZ-binding motif
what are the different types of muscle cellsCardiac muscle - in the wall of heart, adjacent cells connected by electrical conducting junctions to ensure synchronous contraction Skeletal muscle - striated muscle fibres, made from large multinucleated cells. control voluntary movement Smooth muscle - thin elongated cells non striated, control involuntary movement
what are the requirements for a multicellular organismInteractions: Cell adhesion molecules tight junctions, gap junctions, adherens junctions Desomosomes Interactions between cells and their surroundings: Hemidesmosomes and focal adhesions basal lamina Extracellular matrix - integrity of tissues
major classes of cell adhesion moleculesHomophilic interactions: Cadherins (E-cadherin) Ig-superfamily Heterophilic interactions: Integrins (alpha v beta 3) Selectins (P-selectin)
tight junctions?Sometimes cells need to form an impermeable barrier, tight junctions seal gaps between cells, the membranes are firmly pressed together and prevent leakage.
tight junction proteinsThe role of tight junctions are too seal off body cavities and restrict diffusion of membrane components. Proteins: Claudins: important in structure and sealing Occuludins: determins junction permeability
What are gap junctions?Series of pores connecting adjoining cells and forming a cytoplasmic bridge,also provides a chemical and electrical coupling between adjacent cells. Permit the movement ions and small molecules of MW less than 1200 between cells
Gap junction functions?Allow co-ordination of activities in a sheet of cells, example of this is beating cilia, allows rapid transmission of nerve impulses, these impulses can pass through cells, rather than having to jump across synapses. Gap junction are important for intercellular signalling.
Aherens junctions?connect the contractile bundles of actin and myosin filaments that run parallel to the plasma membrane, allows contraction of the epithelial tubes. The loss of cadherin ( protein involved in interaction) is associated with metastasis in cancer
Components of adherens junctionsExternal homotypic interactions between E-cadherins and interactions between catenins and actin microfilaments
What are desmosomes?button like contact points that rivet cells together, connect the intermediate filament networks of adjacent cells Desmosomes anchor the cells cytoskeleton to the PM and connect the cytoskeleton to surrounding cells giving strength
desmosomes and hemidesmosomeswithin the cell, intermediate filaments connect with adjacent desmosomes and hemidesmosomes to produce a cage-like skeleton. Hemidesmosomes anchor the cell to the basal lamina
Integrin-containing junctionsIntegrin-containing junctions connect cells to the substratum Laminin and fibronectin are multi-adhesive proteins that bind to components of the extracellular matrix Multi-adhesive proteins that bind to multiple components of the extracellular matrix and cells
basal lamina?network of proteins and proteoglyans connected to the plasma membrane Specialised region of extracellular matrix that provides a solid substratum to anchor epithelial cells, forms a barrier between epithelial sheets and connective tissue. different forms in different tissue
what is the ECM?ECM is a fibrous network of proteins and polysaccharides that fills the spaces between cells. hold cells and tissues together. role in embryogenesis, wound healing and cell migration. Proteoglycans - protein core linked to glycosamineoglycns form a hydrated gel-like substance into which fibres are embedded Fibrous protein - structural, adhesive or elastic
What does GAGs stand for?glycosaminoglycans
GAGs, what do they do?They occupy much of the extracellular space extremely hydrophilic, adopting extended conformation to form hydrate gels
what are Elastic fibres?allow tissues to stretch and recoil, some tissues need both strength and elasticity (blood vessels) Composed of elastin deposited on glycoprotein-based microfibrils with crosslinks is interwoven with collagens to limit extent of stretching
What are the functions of the plasma membrane?Interface between a cell and its environment Barrier: regulates transportation Attachment point for intracellular cytoskeleton
what is diffusion?the net movement of molecules from a region of a high concentration to a region of lower concentration occurs down a concentration gradient, move down until they are equal
equation of rate of diffusion?(surface area x difference in conc)/thickness of surface
what does rate of diffusion depend on?surface area across within diffusion occurs - larger the SA the faster the diffusion Thickness of surface - thinner the surface the faster the diffusion Difference in con - the larger the difference in conc gradient faster the diffusion Hydrophobicity of a substance, measured by its partition coefficient, K - the higher a substances partition coefficient, the more lipid-soluble it is
what is osmosis?the process by which molecules of a solvent tend to pass through a semipermeable membrane from a low conc to a high conc solution
What are the osmotic effects?Hypertonic - solute is more concentrated causing cells to shrink Isotonic - equal salt and water conc, normal cell shape Hypotonic - lower conc of solute in the cells, causing cells to swell and burst
Differentiate between the different types of transport?Simple diffusion - no transporter molecule is used and transport is according to the concentration gradient Passive transport - transporter molecule is needed but no energy is required as the transport is down the conc gradient,can use channels and occurs spontaneously. Active transport - transporter requires energy to move a substance against the conc gradient, transporters in active transport are called pumps
Membrane permeability?rate of diffusion depends on the permeability coefficient (P) of the membrane to transported solute and its conc on either side of membrane
what does the permeability coefficient depend on?K: partition coefficient (hydrophobicity of solute), D: diffusion coefficient of solute (rate of diffusion across the membrane based on molecular weight / size of solute) Δx: width of the membrane (Δx)
Facilitated transport?If the measured permeability of a solute is higher than expected = facilitated transport Channels form a hydrophilic tube or passageway across the membrane through which multiple water molecules or ions move simultaneously , single file at a very rapid rate. Some channels are open much of a time whereas others require activation upon specific signals. These channels are referred to as gated channels. – very selective.
what are aquaporins?form a pore across the bilayer, its tetramer, selective passage of water molecules shaped like an hourglass.
Name some Ion channels used in facilitated diffusionGated channels - Ligand, voltage, mechanically
Voltage-gated channels?voltage-gated channels respond to changes in the membrane potential. resting varies between -20mV and -200mV interior more negative than exterior.
ligand gated channels?respond to the binding of a ligand, could bind extracellulary (neurotransmitter) or intracellulary (ion or nucleotide)
Mechanically gated?channels respond to mechanical stress, those channels may have cytoplasmic extensions that interact directly with the cytoskeleton.
What is the potassium channelTransfers K+ out of the cell, facilitated diffusion,complex of 4 subunits with a Tepee arrangement main helices tilted at 25 degrees, each subunit contributes an inner pore lining helix and an outer structural helix.
Potassium channelThe central pore is filled with water which allows potassium ions to remain hydrate, Three potassium binding sites each provided from main chain C=O groups. Selectivity filter = Formed from conserved sequence residues 75-79, 75-78 bind potassium in two positions, third ion in cavity. Peptide bond carbonyl groups provide rings of O atoms Electrostatic repulsion ensures high movement throughout
what is selectivity due to in the K+ channelselectivity of K+ is due to a hydration compensation mechanism, rings of oxygen are placed to compensate for loss of K+ hydration shell but not Na+ hydration shell (Na+ is too small to fit into the ring) controlled by a gating mechanism, minor structural changes that serve to obstruct the entrance to the pore.
what are ionophores?Microbial low molecular weight products that make the membrane permeable to ions Gramicidin A 15 residue protein from Bacilus brevis Forms a cation specific pore, requires to molecules Causes equal distribution of K+ and Na+ between environment and cell interior cell death Topical antibiotic
Transporters?Transport can be passive (uniport) or active (symport and antiport) Slower rate than channels Uniporters transport molecules down their conc gradient symporters and antiporters move one against the conc gradient
what are symport and antiportsSymport transports two different substances in the same direction Antiport transports two different substances in opposite directions
Glucose transporter?uniporter -selective for glucose, 12 transmembrane a-helices Facilitated diffusion - requires conc gradient conformational changes allow glucose to move through the protein not flipping
what are the kinetics of passive transport?Simple diffusion = rate is directly proportional to conc of solute, higher the conc of the solute the higher the rat of diffusion Transporter-mediated diffusion = Transporter proteins varying affinity for their solute, have varying maximum rate, when transporter is saturate they will reach maximum rate Analogous to a biochemical enzymatic reaction
what are coupled transporters?they couple the transport of one solute down their conc gradient, with the transport of one solute against their conc gradient
what are light driven pumps?found in bacteria and archaea and couple transport of a solute (H+) from energy from light (bacteriorhodopsin)
atp driven pumps?Use energy released by hydrolysis of ATP to transport ions and molecules against their concentration gradient ATP binding site in the cytosolic side Four main classes P-class: require the catalytic subunits to be phosphorylated as part of transport cycle V-class: not phosphorylated, will transport protons F-class: not phosphorylated, use the conc gradient of protons to synthesis ATP ABC transporters: transfer small molecules and are also found in bacteria
what is sarcoplasmic reticulum?specialised type of endoplasmic reticulum that serves as the intracellular store of Ca2+.
P-type ATPases?sarcoplasmic reticulum Ca2+ pump: - low Ca2+ cpncentration, high within SR - Ca2+ is transported against its conc gradient - Antiporter Na+/K+ ATPase - high conc of Na+ extracellularly, high conc of K+ intracellularly, maintains the conc gradient, Antiport
What type of pump is the calcium pump?its a P-type ATPase, contains multiple transmembrane helices coupled to three domain in the cytosol: The nucleotide binding domain (N), phosphorylation domain (P), and the activator domain (A) N domain = contains the ATP binding site P domain = contains the aspartate that is phosphorylated A domain = contains phosphatase activity that dephosphorylates the phosphorylated P domain
What is the first step in Ca2+ transport?When the ATP pump is in the ATP bound state, the pump is open to the cytosol allowing two calcium ion to bind in a pocket formed by the transmembrane helices.
Second step in Ca2+ transport?when calcium is bound, the pump closes, and ATP is hydrolysed. This results in the transfer of a phosphate group to a conserved aspartate (Aspartate 351) in the P-domain. In this state, the calcium ions are trapped between the helices within the membrane.
Third step in Ca2+ transport?The shift to the E2 state causes ion binding sites to 'evert' so that the ions can dissociate into the luminal side of the membrane. ADP id exchanged for a fresh ATP resulting in the pump to open to the lumen of the SR releasing the calcium ions. binding of 2 H+ from the SR and the closing of the pump and the dephosphorylation of the P-domain
Step four in the Ca2+ transport?In the E2 -P state, the enzyme has low affinity for the Ca2+ ions, so they are released
Step five in the Ca2+ transport?With release of the Ca2+, the phosphoaspartate residue is hydrolyzed, and the phosphate group is released.
Step six in the Ca2+ transport?Does not have a covalently attached phosphate group and therefore not stable so verts back to E1 form. Calcium ATPases play an important role in cell signalling as well as Ca2+ can act as a signalling molecule. Maintaining low concentration of CA2+ inside the cell also allows for the signal to be quickly transmitted.
P-type ATPases Na+/K+Insert 2 potassium ions and remove 3 sodium ions Na+ gradient drives transport of nutrients as with glucose. Regulates cytosolic pH More than 30% of an animal cells energy is used to fuel this pump – nerve cells and cells involved in transport this could increase up to 70%. Electrogenic - drives a net electric current across the membrane. As with the calcium pump an aspartate is phosphorylated
Pumping Na+?Pumping Na+ against its conc gradient requires energy, provided by cleaving ATP, the ATP transfers a phosphate group to the pump in a high energy linkage. Phosphorylation causes a dramatic change in the pumps conformation, sodium ions become exposed and released outside of the cell. This also exposes binding sites for potassium ions in the pump. There are two potassium-binding sites, binding of the potassium ions triggers release of the phosphate group and return the pump to its normal conformation
Summery of P-type ATPaseCreates a sodium and potassium concentration gradient Pump is electrogenic Per 1 ATP hydrolysed, 3 Na+ ejected, 2 K+ taken up, 1 positive charge ejected ts action creates an electrical potential difference across the plasma membrane Antiporter, up-hill glucose transport, net carbohydrate and protein absorption, cell volume, resting potential
V-type ATPases?found in Eukaryotes 13 subunits stands for vacuolar transporters Transports protons across internal membranes They generate the low pH of plant vacuoles and of lysosomes and other acidic vesicles in animal cells by pumping protons from the cytoplasm to the lumen of the organelle.
F-type ATPases?Found in bacterial plasma membranes, mitochondria and chloroplasts Reverse proton pumps (ATP synthase) Use the energy from proton gradient to synthesise ATP
ABC (ATP binding cassettes) transport protein?When ATP is not bound the binding site is in the cytosol, when atp is bound the binding site is open at the ectracellular side. 78 ABC transporters in E.coli – mono and polysaccharides, peptides, lipids, drugs and even proteins.
Multidrug resistance protein (MDR)ABC transporter highly expressed in many human cancer cells Pump drugs out of the cell Makes cells resistant to various cytotoxic drugs used in cancer chemotherapy
what is so special about proteins, DNA and RNA?all molecules conform to physical and chemical laws nucleic acids and the protein they encode display properties appearing to transcend these laws (life) Proteins act s cellular components with very precise structures, defined by sequence information Many proteins are highly specific catalysts allow large number of chemical reactions in the cell without interfering with each other.
what is the importance of protein structure?The importance of the protein structure is that anything that needs to be bind is bound in the right position to give the desired effect. EXAMPLE: for lysozyme, binding to the polysaccharide substrate is very specific, each atom making contact is in precisely the right position for binding and catalysis. Lysozyme is part of the innate immune system. The specificity of reaction is determined by the precise array of charges and hydrophobic elements in the protein ie. by exact structure of each protein, this structure is determined by the sequence of AA in the polypeptide chain, which is in turn determined by the DNA bases encoding this gene.
The central dogma molecular biology- info in DNA conserved with high fidelity by DNA replication - during gene expression, info is passed from DNA to mRNA - The info then passes from mRNA to protein by translation (translating the info from a nucleotide language to an amino acid language)
what are genomes?The genomes is the total of all genes
What are genes made of?genes are made from DNA, however virus genes are made of DNA or RNA The role of DNA is to encode proteins
Why are genes switched on and off in different tissues?some are always on, known as housekeeping genes (genes encoding enzymes for glucose metabolism or protein synthesis) Other genes are only switched on in cells where needed eg. muscle myosin genes, B-lymphocytes in immune system.
Are genes lost when they are not used in the cell?genes are not lost when not in use. If the nucleus from a differentiated cell is transplanted to an empty egg a complete animal can be produced and therefore shows that genes are not lost.
Problems with human cloning?Technical problems, many ethical issues to be addressed, potential of defective babies. more realistically used to produce stem cells for therapy eg. neurodegenerative diseases and diabetes
What is the difference between reproductive and therapeutic nuclear transplantation?Therapeutic cloning is the technique that is used to develop specialised cells for stem cell therapy whereas reproductive cloning is using the nucleus from one 'being' and an egg cell from another and producing an exact living clone.
Explain how DNA was established as the molecule that carries inherited info?- In the 1920’s Fred Griffith reported that a “heat-killed extract” from pathogenic bacteria could convert harmless ones to pathogenic ones. - Purified DNA was shown to produce the same effect. Genetic properties can be transferred from one bacterial strain to another by extracting DNA from the first strain and adding to another strain (Transformation)