Molecular genetics

Question 1

Chromatin threads

Answer 1

• made up of histone proteins coiled arnd deoxyribonucleic acid (DNA)

Question 2

How is DNA organised inside cell nucleus (each DNA molecule)

Answer 2

• consists of 2 anti-parallel strands, twisted arnd each other, double helix
• wrapped arnd histone proteins
• during cell div, chromatin threads coil tightly to form chromosome

Question 3

Define DNA

Answer 3

• molecule that carries genetic info
• made up of nucleotides (basic unit of DNA)
• each DNA nucleotide made up of
  1. a deoxyribose (sugar) molecule
  2. phosphate group
  3. a nitrogen-containing base

Question 4

Nitrogen-containing base

Answer 4

• 4 types
• adenine (A)
• cytosine (C)
• guanine (G)
• thymine (T)

Question 5

Polynucleotides

Answer 5

• formed when nucleotides join tgt by condensation
• DNA molecule made of 2 anti-parallel polynucleotide strands (double-helix)
• bases of both strand form tgt according to rule of base pairing

Question 6

Rule of base pairing

Answer 6

• Adenine and thysine (A&T)
• Cytosine and guanine (C &G)
• complementary bases
• 1:1 ratio for A:T and G:C

Question 7

Define gene

Answer 7

• segment of DNA
• specific sequence of nucleotides
• controls synthesis of specific polypeptide

Question 8

Codon

Answer 8

• triplet code, 3 nucleotides forms an amino acid

genetic code states which amino acid each triplet code is for

Question 9

What happens when nucleotide sequence is altered?

Answer 9

• known as gene mutation

- may or may not lead to change in protein product

Question 10

Examples of gene mutation

Answer 10

• refers to change in genetic material of a gene
• e.g albinism, gene that cause absence/defect in melanin (enzyme that produces pigment)
• e.g. sickle-cell anaemia, mutation in gene that causes protein product to differ from normal protein by 1 amino acid, RBC become sickle shaped

Question 11

How are proteins made?

Answer 11

• transcription

- translation

Question 12

Transcription (brief overview)

Answer 12

• DNA separate out, 1 template DNA (Strand), 1 non-template DNA
• occurs when DNA template transcribed into mRNA
• occurs in nucleus of cell
• DNA triplet code converted into mRNA codons

Question 13

Translation (brief overview)

Answer 13

• mRNA molecule translated into polypeptides

- occurs in cytoplasm of cell

Question 14

DNA vs RNA (sugar unit)

Answer 14

• DNA: deoxyribose

- RNA: ribose

Question 15

DNA vs RNA (nitrogenous bases)

Answer 15

• DNA: Adensine (A), Thymine (T), Guanine (G), Cytosine (C)

- RNA: Uracil (U) instead of Thymine (T), rest same

Question 16

DNA vs RNA (ratio of nitrogenous bases)

Answer 16

• DNA: A:T=1:1, G:C=1:1 (becos double helix, each base has a partner)
• RNA: no fixed ratio (single-stranded, each base no partner)

Question 17

DNA vs RNA (size and solubility)

Answer 17

• DNA: large, insoluble molecule (cannot leave nucleus)

- RNA: small, soluble molecule (can leave nucleus)

Question 18

DNA vs RNA (temporary vs permanent)

Answer 18

• DNA: permanent molecule in nucleus

- RNA: temporary molecule, made when needed

Question 19

Translation (biological molecules involved)

Answer 19

1. Amino acids: 20 types
2. Transfer RNA molecules: tRNA, each has aa attached, aa attached depends on tRNA’s anticodon
3. Ribosomes: help make polypeptides from mRNA
4. mRNA molecules

Question 20

What happens during transcription? (4)

Answer 20

1. Gene unzips
2. DNA template formed in nucleus
3. mRNA formed, complementary copy which contains uracil instead of thymine
4. mRNA exits out of nucleus and enters cytoplasm

Question 21

What happens during translation? (6)

Answer 21

1. mRNA attaches to ribosome
2. tRNA with anticodon complementary to mRNA attaches to ribosome as ribosome moves along mRNA strand
3. amino acids attached to tRNA forms peptide bonds with each other
4. tRNA gets released, a new one fits into ribosome
5. amino acids continually attached until ribosome reaches stop codon on mRNA, ribosome leaves mRNA
6. complete polypeptide produced (chain of aa)