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

Location of Spermatogenesis

Testes

Location of Oogenesis

Ovary

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]