6) Nucleic Acids & Protein Synthesis

Question 1

what are the 3 components of a nucleotide ?

Answer 1

• nitrogenous base
• pentose sugar (deoxyribose/ribose)
• phosphate group

Question 2

what are the 3 components of ATP?

Answer 2

• adenine
• ribose
• phosphate (3)

Question 3

what bases are purines and what are pyrimidines?

Answer 3

purines (bigger) - adenine & guanine
pyrimidines (smaller) - thymine/uracil & cytosine

Question 4

what structure do purines have compared to pyrimidines ?

Answer 4

purines (bigger)- double ring structure
pyrimidines (smaller)- single ring structure

Question 5

how many hydrogen bonds are there between adenine and thymine ?

Answer 5

2

Question 6

how many hydrogen bonds are there between guanine and cytosine ?

Answer 6

3

Question 7

which bases pair with which ?

Answer 7

A - T
G - C

Question 8

describe the structure of DNA

Answer 8

• double helix
• antiparallel strands
• 5’ to 3’ & 3’ to 5’ (opposite strand)

Question 9

what bonds link the nucleotides

Answer 9

phosphodiester bonds

Question 10

give 3 differences between the structure of DNA & RNA

Answer 10

DNA
- v long strands
- sugar is deoxyribose
- bases are A, T ,C ,G (no U)
- 2 polynucleotide strands

RNA
- short strands
- sugar is ribose
- bases are A, U, C, G (no T)
- single polynucleotide strand

Question 11

what is the function of helicase

Answer 11

unwinds the double helix at replication forks

Question 12

function of primase

Answer 12

synthesises the RNA primer

Question 13

function of DNA polymerase III

Answer 13

synthesises the new strand of DNA by adding ACTIVATED nucleotides onto the primer in a 5’ to 3’ direction

• forms phosphodiester bonds

Question 14

function of DNA polymerase I

Answer 14

removes the primer & replaces it with DNA

• forms phosphodiester bonds

Question 15

function of DNA ligase

Answer 15

joins the ends of DNA and Ozaki fragments ON LAGGING STRAND

• forms phosphodiester bonds between fragments

Question 16

explain the leading strand

Answer 16

Dna polymerases can move in the same direction as the replication fork so replication is continuous.

Question 17

explain the lagging strand

Answer 17

DNA polymerases have to move in the opposite direction to the replication fork, so replication is discontinuous.

Question 18

what is a gene ?

Answer 18

a sequence of nucleotides that code for a polypeptide

Question 19

whats a universal code

Answer 19

almost every organism uses the same code - same codons code for the same amino acids in all living things

Question 20

whats a degenerate code

Answer 20

multiple codons coding for the same amino acids

Question 21

whats a gene mutation

Answer 21

change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide

Question 22

What are the 3 ways a gene mutation can be caused by?

Answer 22

1. substitution
   : (best case) degenerate, as even if base changes = same amino acid.
   : (worst case) 1 amino acid changes
   = whole protein.
   : worse if stop codon changes
2. deletion (non-functional protein)
3. insertion (non-functional protein)

Question 23

outline the stages of transcription

Answer 23

• DNA unwinds by RNA polymerase
• H bonds break
• one strand acts as template
• RNA polymerase recognises and binds to the promoter
• RNA polymerase adds RNA nucleotides to exposed DNA strands.
• phosphodiester bonds formed
• product = messenger RNA

Question 24

describe the role of tRNA in protein synthesis

Answer 24

• tRNA carries amino acid to rbisomes.
• each type of tRNA carries specific amino acid.
• anticodon on tRNA binds to codon on mRNA.
• tRNA holds amino acids in place.
• tRNA molecules reused

Question 25

how is the length of RNA molecule shortened

Answer 25

• introns are removed (splicing)
• exons are joined together (primary transcript)

Question 26

outline the stages of translation

Answer 26

• mRNA used as template
• mRNA translated 5’ to 3’ direction
• binding of ribosome to mRNA
• first TRNA binds to start codon
• second tRNA binds to ribosome
• mRNA read in base triplets
• tRNA bring amino acids
• peptide bonds btwn amino acids
• reach a stop codon