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DNA, Genes and the Continuity of Life


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DNA, Genes and the Continuity of Life


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Rahil Mehta


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[Front]


Nitrogen Base
[Back]


Makes up the "rungs" of the DNA ladder

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DNA, Genes and the Continuity of Life - Detalles

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Nitrogen Base
Makes up the "rungs" of the DNA ladder
Sugars and phosphates
Alternate along the "sides" of the DNA ladder
Nucleotide
Made up of a pentose sugar, phosphate, and a nitrogen base
Double Helix
The shape of the DNA molecule
RNA
Uses the code from DNA to make proteins
How is DNA different from RNA?
DNA has Thymine and is double stranded, RNA has Uracil and is single stranded
Trait
A characteristic that an organism can pass on to its offspring through its genes.
Gene
A segment of DNA on a chromosome that codes for a specific trait
Chromosomes
Thread-like structures made of bundled up DNA molecules that contain the genes
How is DNA different from RNA?
DNA has Thymine, RNA has Uracil DNA has deoxyribose, RNA has ribose DNA is a double helix, RNA is a single helix
Hydrogen bond in DNA
A weak chemical bond that holds together, the complementary strands of DNA. The hydrogen bonds and the nitrogen bases form the rungs of the DNA.
Helicase
Unzips DNA
Primase
An enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template.
DNA Polymerase
Builds new DNA strand by adding complementary nucleotides
Ligase
An enzyme that connects (Glues) two fragments of DNA to make a single fragment
Leading Strand
The new continuous complementary DNA strand synthesized along the template strand in the mandatory 5' to 3' direction.
Lagging Strand
The strand that is synthesized in fragments using individual sections called Okazaki fragments. from 3' to 5'
DNA Replication Steps
1) Helicase- unwinds the parental double helix 2) DNA topoisomerase - upstream of helices alleviating torsional strain 3) Single-strand binding proteins (SSBP) stabilize unwound DNA, aided by DNA gyrase. 4) Primase synthesizes a short RNA primer for DNA polymerase to bind to in the 5' to 3' direction to start replication on each strand. 5) DNA polymerase synthesizes the leading strand in 5' to 3' direction while the lagging strand is made discontinuously by primase making short pieces and then DNA polymerase extending these to make Okazaki fragments. 6) DNA ligase joins the Okazaki fragments together
Antiparallel
The opposite arrangement of the sugar-phosphate backbones in a DNA double helix.
Prokaryotes
Lack distinct nucleus,
Diploid
Cell containing two complete sets of chromosomes from each parent
Haploid
Cell containing single set of unpaired chromosomes, one from each parent
Homologous Chromosomes
Set of chromosomes [one paternal, one maternal], containing the same genes but different alleles
Human Karyotype
Set of 46 chromosomes: 23 pairs
Autosomal Chromosomes
Non-sex chromosomes, pairs 1-22 are autosomal [no. 23 determines sex: Female = XX, Male = XY
Genes
Segment of DNA coding for a specific phenotypic trait [e.g. gene for hair colour]
Gene Locus
Fixed point on the chromosome where a specifc gene is found [e.g. location on a chromosome of the hair colour gene]
Alleles
Different variations of a gene, all originating from mutations [e.g. blond, brown, black hair colour]
Meiosis
Cell division resulting in four genetically unique daughter cells [gametes] each with half the number of chromosomes [haploids] as the parent cell [diploids]
Crossing Over + Recombination
- Occurs during Prophase I - Homologous Chromosomes: each consisting of two sister chromatids, line up together forming a tetrad - One chromatid from each homologous pair cross over at points called chaisma, and genes/alleles are exchanged
Definition of Spermatogenesis
Production of sperm from spermatogonia
Definition of Oogenesis
Production of eggs form oogonia
Continuity of Spermatogenesis
Continuous since puberty
Continuity of Oogenesis
Discontinuous process: early stages in faetus, continuing post puberty
Cytokinesis of Spermatogenesis
Four haploid sperm cells produced [4 spermatozoa]
Cytokinesis of Oogenesis
One oogonium produces one ovum, and three polar bodies which get degraded and reabsorbed.
Independent Assortment
Chromosomes and associated genes separate independently from non-homologous chromosomes when gametes form
Random Fertilisation
Unpredictable union of gametes during sexual reproduction, contributing to genetic diversity in offspring through the chance combination of different alleles from each parent.
Fertilisation
Fusion of two haploid gametes results in the formation of a diploid zygote → zygote divides to multiply, producing an embryo.
Genes
Region(s) of DNA that are made up of nucleotides [molecular unit of heredity]. Code for a specific phenorypic trait.
Alleles
Different variations of a gene. All alleles originated from mutations
Genome
All the genetic material in the chromosomes of an organism [including genes, DNA sequences]
Role of non-coding DNA
Determne when/where coding regions are turned on/off
Non-coding DNA
Transcribed proteins (e.g., tRNA), centromeres, telomeres, and introns [within or between protein-coding genes]
Introns and Intergenic regions
Provide a binding site for specialised proteins called transcription factors which can either activate [promoters] or suppress [silencers] transcription.
Exons
Coding regions of DNA
Introns
Non-coding regions of DNA
Centromeres
Specialized DNA region on a chromosome where spindle fibers attach during cell division, ensuring accurate distribution of genetic material between daughter cells.
Telomeres
Form protective caps at the end of chromosomes [essential for correct chromosomal replications]
Transcription
Process by which a DNA sequence is used as a template to make an mRNA copy of a gene
MRNA
Single-stranded molecule of mRNA that corresponds to the genetic sequence of a gene and is read by a ribosome in the process of synthesising a protein
Process of mRNA Production
1. Initiation: RNA polymerase binds to the promoter region of a gene on the DNA template in the nucleus. 2. Elongation: RNA polymerase moves along the DNA strand, unwinding it and adding complementary RNA nucleotides (A, U, G, C) to the growing mRNA strand. 3. Termination: Transcription concludes as RNA polymerase reaches the terminator sequence, causing mRNA and RNA polymerase to detach from the DNA template. 4. mRNA Processing: In eukaryotes, pre-mRNA undergoes modification, including capping at the 5' end and addition of a poly-A tail at the 3' end, along with removal of introns by splicing. 5. Export: Processed mRNA exits the nucleus and enters the cytoplasm.
MRNA Translation
Converting nucleic acid in the form of mRNA into a protein. A polypeptide is formed according to the sequence of codon.
Process of mRNA Translation
1. Initiation: The small ribosomal subunit binds to the mRNA near the start codon (AUG), followed by the attachment of the initiator tRNA with the complementary anticodon (UAC). 2. Elongation: The ribosome moves along the mRNA in a 5' to 3' direction. Each new tRNA brings an amino acid, forming a peptide bond between adjacent amino acids. The ribosome shifts, translocating the mRNA and tRNAs. 3. Termination: When a stop codon (UAA, UAG, or UGA) is reached, release factors bind to the ribosome, causing the completed protein to detach. 4. Protein Folding: The newly synthesized polypeptide undergoes folding, guided by its amino acid sequence and cellular environment. 5. Protein Function: The mature protein carries out its specific role in cellular processes. This process occurs on ribosomes in the cytoplasm and synthesizes proteins based on the mRNA sequence.
Gene Expression
Process by which information stored in a gene is used to synthesise a functional gene product
Gene Regulation
Process of controlling which genes are expressed by which cells, when they are expressed, and in what quantity [which, when and what]
Transcription Factors
Proteins produced by regulatory gene
Translation Factors
MRNA finds a complementary mRNA and an enzyme then breaks it
Gene Cascades
Chain reaction in which the expression of one gene causes subsequent gene expression [Due to gene 1 producing a transcription factor to trigger gene 2]
Phenotypic Expression
The expression of physically observable traits
Epigenome Factors affecting Phenotypic Expression
Produce tags which determine which genes are ex/repressed.
Environmental Factors affecting Phenotypic Expression
External conditions, like temperature, nutrition, light, chemicals, stress, and social interactions, can alter gene activity and protein function - influences how traits encoded by genes are expressed
Differentiation Cell Regulation
Process by which different types of stem cells become specialised in order to perform different functions [affected by transcription and growth factors]
HOX Genes
Group of genes that control the body plan and segment identity during development. They regulate the spatial arrangement of body structures along the anterior-posterior axis in organisms. Produce transcription factors in a specific order
Sex-Determining Region Y
Located on the short arm of the Y chromosome, codes for SRY protein. Transcription factor to promote genes associated with testes formation and inhibits genes linked with female reproduction. [Transcription of SOX-9]
Mutations
Permanent change in the nucleotide sequence of DNA
Somatic Mutation
Mutation occuring in a body cell - not passed on to offspring
Gametic Mutation
Mutation occuring in a sex cell - heritable, form new alleles - cause variation
Point Mutation
Change, deletion, or insertion of a singular nucleotide base during replication
Frameshift Mutation
Occurs when theres a deletion or insertion as this completely shifts the mRNA sequence of 3 codons, shifting all subsequent sets of 3
Mutagen
Physical, chemical or biological agent causing mutation
UV/Radiation Mutagen
High energy waves ionise atoms → DNA damaged = mutation
Temperature Mutagen
Breaks bonds between deoxyribose sugar → mutates
Chemical Mutagen
Base analogues mimic and insert themselves into DNA bases
Non-Disjunction Mutations
Homologous chromosomes or sister chromatids fail to separate → daughter cells contain wrong number of chromosomes [Aneuploidy]
Monosomy
Form of aneuploidy wherein one chromosome is missing [Turner Syndrome]
Trisomy
A form of aneuploidy in which a homologous set contains an extra chromosome [3 instead of 2]
Trisomy-21
Down Syndrome: Set 21 has 3 chromosomes
Mosaicism
Somatic mutation in which an individual has two genetically different sets of cells in their body
Autosomes
44 non-sex linked chromosomes
Autosomal Dominant Alleles
Dominant allele carried on an autosome
Pure Breeding
Only possessing homozygous recessive or dominant
Sex-Linked Inheritance
Allele carried on one of the sex chromosomes [commonly X since more genes present than Y]
Polygenic Inheritance
Phenotypic trait determined by 2 or more genes [Not Mendellian dominant/recessive, contributing allele (T) vs non contributing allele (t)
Co-Dominance
Pair of alleles expressed equally in the phenotype of a heterozygous individual [use superscripts]
Blood Types
Different groups based on surface glycoprotein [antigen] structure. [A and B are co-dominant, O is recessive]
Incomplete Dominance
2 heterozygous alleles cross to make a new allele by blending [White rose + Red rose = Pink rose]
Recombinant DNA
Result of combining DNA of two different species
Isolation of DNA
Restriction enzymes are used in bacteria to find a recogntion site [to code sequences] along DNA and cut it at that point, using the same enzyme, gene is inserted into a plasmid
Transfer of DNA
Plasmid vector used to transfer the DNA
Rejoining DNA
DNA ligases used to join fragments together. Same recognition enzyme must sever the strand in the second organism so base pairs match with the fragment.
Amplification of DNA
Transformed bacterial cells with the recombinant DNA allowed to multiply in a large scale culture → divide and replicate; rDNA replicated → amplification of the desired sequence
Short Tandem Repeats
Short sequence of DNA - normally 2-5 base pairs repeated
Short Tandem Repeats
Short sequence of DNA - normally 2-5 base pairs repeated [no. varies person to person]
DNA Sequencing/Profiling
Process of determining the precise order of nucleotides within a sample of DNA, involves testing of highly variable regions of DNA containing STR → located in introns
Polymerase Chain Reaction
Technique used to exponentially amplify the number of copies of a specific DNA sequence [DNA samples typically found in trace amounts → must be amplified]