Chapter 8 - DNA Flashcards
Direction of DNA synthesis
& Direction of reading of DNA
Direction of synthesis: 5’ > 3’
Direction of reading: 3’ > 5’
Structure of Chromosones
DNA polymer is wound around proteins called histones which organise themselves into groups which coil in loops in order to create the chromosome.
DNA Synthesis leading strand
Helicase: - Splits DNA double helix
DNA polymerase III: Synthesis DNA in direction 5’ >3’
DNA Synthesis complementary strand
Helicase: - Splits DNA double helix
RNA Polymerase II: Synthesises short RNA primer
DNA Polymerase III: Synthesis DNA okazaki fragments in direction 5’ >3’
DNA Polymerase I: Replaces RNA primer with DNA
DNA Ligase: bonds neighbouring okazaki fragments together
DNA —-> Protein
- Enzyme unwinds DNA double helix
- Transcription: Free RNA complementary to the template strand form mRNA with the help of RNA polymerase enzyme
- Splicing: Introns are removed from base sequence and methylated cap is added
- Translation: Ribosome bind to methylated cap. Ribosomal subunits join together and begin to synthesis protein from start sequence to end.
tRNA anticodons bind to the complementary codons and add corresponding amino acid to polypeptide chain.
Differences between DNA and RNA
DNA: Double stranded, one less oxygen, carries all genetic info
RNA: Single stranded, U replaces T, Carries only info required for protein synthesis.
Triplet Vs codon Vs Anti-codon
Triplet: DNA sequence 3 bases long which codes for one amino acid
Codon: mRNA sequence 3 bases long which codes for one amino acid
Anticodon: tRNA sequence 3 bases long which codes for one amino acid
Examples of Purines & Pyrimidines
Purine: Adenine & Guanine ( contain “a” & “nine”)
Pyrimidines : Cytosine, Thymine and Uracil
DNA/mRNA Pairing
A & T/U
G & C
Bond created during condensation polymerisation of nucleic acids.
Phosphodiesther bond
Role of operator in Gene regulation
Region of DNA situated around the promoter which acts as a binding site for a specific repressor protein.
Role of promotor in gene regulation
Non-coding base sequence that signals the start of a gene and acts as a binding site for RNA polymerase.
What is an operon
A functioning set of genomic DNA containing a cluster of genes under the control of a single promoter.
Role of repressor protein in gene regulation
Repressor protein binds to operator, disallowing the RNA polymerase to bind to the neighbouring promotor thus stopping translation from occurring.
Role of enhancers in gene regulation
Found in Eukaryotic DNA.
Increase number of RNA polymerase molecules transcribing each gene, thus increasing rate of protein synthesis.
How histones chemically modify DNA
DNA wraps around histone protein when chromosones form.
Chemically altered histones can add methyl groups and chemically alter DNA making it impossible for certain sections of DNA to be transcribed, hence influencing gene expresion
Types of Chromosome mutations:
Deletion: Part of chromosome deleted
Inversion: Portion of DNA is flipped within a chromosome
translocation: Part of chromosome is removed from one chromosone and attached to another.
Duplication: Section of chromosome duplicates
Aneuploidy condition and cause
Is the addition or loss of a chromosome from a cell.
Occurs due to non-disjunction in anaphase 1 of meiosis.
Polyploidy condition and cause
Condition where cells contain more than two sets of homologous chromosomes.
Occurs when cell division fails all together in meiosis.
Occurs frequently in plants but never in animals
Neutral point/ silent mutation:
Substituted base pair results in subsequent triplet coding for same amino acid.
Missense Mutation:
Substituted base pair results in on amino acid being substituted for another in the polypeptide chain, hence changing slightly protein shape and function.
Nonsense mutation:
Substituted base pair change the triplet from coding an amino acid to a stop transcription. If this occurs early in polypeptide chain, function of protein is greatly impacted.
Frameshift mutation
Consequence of addition and deletion mutations which changes the frame of reading for triplets.
Post Transcription modification
5’ - Methyl cap
3’ Poly (A) tail
splicing:
Introns removed
Transcription
- ) Enzyme binds to double stranded DNA an unwraps breaking hydrogen bond between strands and exposing the base pairs.
- ) RNA polymerase bonds to promoter of the template strand and synthesises mRNA in the direction of 5’ to 3’, the mRNA sequence determined by their commentary DNA base pairs on the the plate strand until stop triplet is reached.
- ) post transcription modification occurs to mRNA strand.
Translation
mRNA strand binds to ribosome. Each codon of mRNA forms complementary pair with a tRNA triplet which adds an amino acid to the growing polypeptide chain/
Mitochondrial Vs Chloroplast Vs Nuclear DNA (Eukaryotes) shape
Mitochondrial And Chloroplast = circular.
Nuclear = linear
Redundant DNA
Multiple triplets coding for the same amino acids
