6. Inheritance, Variation and Evolution (reproduction)

Question 1

What are DNA nucleotides made up of?

Answer 1

• common sugar
• phosphate group
• One of four bases

Question 2

What are the bases of DNA (full names)?

Answer 2

• Adenine
• Thymine
• Cytosine
• Guanine

Question 3

Describe how nucleotides interact to form a molecule of DNA?

Answer 3

• Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand
• Base connected to each sugar
• Complementary bases joined by weak hydrogen bonds

Question 4

What are the complementary base pairs?

Answer 4

• A pairs with T
• C pairs with G

Question 5

Explain how a gene codes for a protein

Answer 5

• a sequence of three bases in a gene forms a triplet
• each triplet codes for an amino acid
• the order of amino acids determine the structure (i.e. how it will fold) and function of protein formed

Question 6

Why is the ‘folding’ of amino acids important in proteins such as enzymes?

Answer 6

The folding of amino acids determine the shape of the active site which must be highly specific to the shape of its substrate

Question 7

What is protein synthesis?

Answer 7

The formation of a protein from a gene

Question 8

What are the two stages of protein synthesis?

Answer 8

1. Transcription
2. Translation

Question 9

What does transcription involve?

Answer 9

The formation of mRNA from a DNA template

Question 10

Outline transcription

Answer 10

1. DNA double-helix unwinds
2. RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand
3. RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand
4. mRNA formation complete. mRNA detaches and leaves the nucleus

Question 11

What does translation involve?

Answer 11

A ribosome joins amino acids in a specific order dictated by mRNA to form a protein

Question 12

Outline translation

Answer 12

1. mRNA attaches to a ribosome
2. Ribosome reads the mRNA bases in triplets. Each triplet codes for one amino acid which is brought to the ribosome by a tRNA molecule
3. A polypeptide chain is formed from the sequence of amino acids which join together

Question 13

What is a mutation?

Answer 13

• A random change in the base sequence of DNA which results mostly in no change to the protein coded for, or genetic variants of the protein
• mutations occur continuously

Question 14

Describe the effect of a gene mutation in coding DNA?

Answer 14

• If a mutation changes the amino acid sequence, protein structure and function may change (an enzyme may no longer fit its substrate binding site or structural protein may lose its strength)
• if a mutation does not change the amino acid sequence, there is no effect on protein structure or function

Question 15

What is non-coding DNA?

Answer 15

DNA which does not code for a protein but instead controls gene expression

Question 16

Describe the effect of a gene mutation in non-coding DNA?

Answer 16

Gene expression may be altered, affecting protein production and the resulting phenotype