6 - Nucleic acids and protein synthesis

Question 1

What is a gene?

Answer 1

A sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids, that in turn make up a specific polypeptide (protein)

Question 2

(___) gene(s) code(s) for (___) mRNA molecule(s), which code(s) for (___) polypeptide(s)

Answer 2

One gene codes for one mRNA molecule, which codes for one polypeptide.

Question 3

What is a codon?

Answer 3

A sequence of 3 bases (triplet) which codes for one amino acid

Question 4

How many different amino acids do our cells use?

Answer 4

20

Question 5

How many different triplet combinations are possible?

Answer 5

64

Question 6

Do the same codons code for the same amino acids in all living things?

Answer 6

Yes.

Question 7

What stages make up protein synthesis?

Answer 7

1 - transcription - DNA is transcribed → mRNA molecule produced.
2 - translation - mRNA is translated → amino acid sequence is produced.

Question 8

Where in the cell does transcription occur?

Answer 8

Nucleus

Question 9

What steps occur in transcription?

Answer 9

1 - part of a DNA molecule unwinds (H-bonds between base pairs break) → exposes gene to be transcribed
2 - complementary copy of code from gene is made (single-stranded mRNA molecule)
3 -

Question 10

PMT

Question 11

Name the pentose sugars in DNA and RNA

Answer 11

Deoxyribose in DNA
Ribose in RNA

Question 12

Describe the structure of DNA

Answer 12

Double-stranded polymer of nucleotides twisted to form a double helix.
Nucleotides joined by phosphodiester bonds.
Hydrogen bonds form between complementary base pairs (A+T, C+G).
Antiparallel strands.

Question 13

What are the two groups of nucleotide bases?

Answer 13

Purine
Pyrimidine

Question 14

Name the purine bases and describe their structure

Answer 14

Two-ring molecules:
Adenine - C₅H₅N₅
Guanine - C₅H₅N₅O

Question 15

Name the pyrimidine bases and describe their structure

Answer 15

One-ring molecules:
Thymine - C₅H₆N₂O₂
Cytosine - C₄H₅N₃O
Uracil - C₄H₄N₂O₂

Question 16

What is complementary base pairing?

Answer 16

Describes how H-bonds form between complementary purine and pyrimidine bases.
2 bonds between A+T (or A+U)
3 bonds between G+C

Question 17

Why is DNA replication described as semiconservative?

Answer 17

Strands from original DNA molecule act as templates.
New DNA molecule contains 1 old strand and 1 new strand

Question 18

How is a new strand formed during semiconservative replication?

Answer 18

1 - Free nucleotides from nuclear sap attach to exposed bases via complementary base pairing
2 - DNA polymerase joins adjacent nucleotides on new strand in a 5’ → 3’ direction via condensation reactions to form phosphodiester bonds.
3 - Hydrogen bonds form between complementary base pairs.

Question 19

Outline the role of DNA ligase in DNA replication

Question 20

ChatGPT

Question 21

What components make up a nucleotide?

Answer 21

A phosphate group, a sugar and a nitrogenous base.

Question 22

What is the structure of adenosine triphosphate (ATP)?

Answer 22

ATP is a phosphorylated nucleotide with three phosphate groups

Question 23

Differentiate between purines and pyrimidines, and provide examples of each.

Answer 23

Purines:
Adenine and Guanine
Characterised by: double-ring structure.
Pyrimidines:
Cytosine, Thymine (DNA) and uracil (RNA)
Characterised by: single-ring structure.