Chapter 8 - DNA

Question 1

Direction of DNA synthesis

& Direction of reading of DNA

Answer 1

Direction of synthesis: 5’ > 3’

Direction of reading: 3’ > 5’

Question 2

Structure of Chromosones

Answer 2

DNA polymer is wound around proteins called histones which organise themselves into groups which coil in loops in order to create the chromosome.

Question 3

DNA Synthesis leading strand

Answer 3

Helicase: - Splits DNA double helix

DNA polymerase III: Synthesis DNA in direction 5’ >3’

Question 4

DNA Synthesis complementary strand

Answer 4

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

Question 5

DNA —-> Protein

Answer 5

• 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.

Question 6

Differences between DNA and RNA

Answer 6

DNA: Double stranded, one less oxygen, carries all genetic info
RNA: Single stranded, U replaces T, Carries only info required for protein synthesis.

Question 7

Triplet Vs codon Vs Anti-codon

Answer 7

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

Question 8

Examples of Purines & Pyrimidines

Answer 8

Purine: Adenine & Guanine ( contain “a” & “nine”)

Pyrimidines : Cytosine, Thymine and Uracil

Question 9

DNA/mRNA Pairing

Answer 9

A & T/U

G & C

Question 10

Bond created during condensation polymerisation of nucleic acids.

Answer 10

Phosphodiesther bond

Question 11

Role of operator in Gene regulation

Answer 11

Region of DNA situated around the promoter which acts as a binding site for a specific repressor protein.

Question 12

Role of promotor in gene regulation

Answer 12

Non-coding base sequence that signals the start of a gene and acts as a binding site for RNA polymerase.

Question 13

What is an operon

Answer 13

A functioning set of genomic DNA containing a cluster of genes under the control of a single promoter.

Question 14

Role of repressor protein in gene regulation

Answer 14

Repressor protein binds to operator, disallowing the RNA polymerase to bind to the neighbouring promotor thus stopping translation from occurring.

Question 15

Role of enhancers in gene regulation

Answer 15

Found in Eukaryotic DNA.

Increase number of RNA polymerase molecules transcribing each gene, thus increasing rate of protein synthesis.

Question 16

How histones chemically modify DNA

Answer 16

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

Question 17

Types of Chromosome mutations:

Answer 17

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

Question 18

Aneuploidy condition and cause

Answer 18

Is the addition or loss of a chromosome from a cell.

Occurs due to non-disjunction in anaphase 1 of meiosis.

Question 19

Polyploidy condition and cause

Answer 19

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

Question 20

Neutral point/ silent mutation:

Answer 20

Substituted base pair results in subsequent triplet coding for same amino acid.

Question 21

Missense Mutation:

Answer 21

Substituted base pair results in on amino acid being substituted for another in the polypeptide chain, hence changing slightly protein shape and function.

Question 22

Nonsense mutation:

Answer 22

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.

Question 23

Frameshift mutation

Answer 23

Consequence of addition and deletion mutations which changes the frame of reading for triplets.

Question 24

Post Transcription modification

Answer 24

5’ - Methyl cap
3’ Poly (A) tail
splicing:
Introns removed

Question 25

Transcription

Answer 25

1. ) Enzyme binds to double stranded DNA an unwraps breaking hydrogen bond between strands and exposing the base pairs.
2. ) 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.
3. ) post transcription modification occurs to mRNA strand.

Question 26

Translation

Answer 26

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/

Question 27

Mitochondrial Vs Chloroplast Vs Nuclear DNA (Eukaryotes) shape

Answer 27

Mitochondrial And Chloroplast = circular.

Nuclear = linear

Question 28

Redundant DNA

Answer 28

Multiple triplets coding for the same amino acids