Protein Synthesis

Question 1

Name the purine bases and describe their structure

Answer 1

Adenine C5 H5 N5

Guanine C5 H5 N5 O

Question 2

Name the pyrimidine bases and describe their structure

Answer 2

Thymine C5 H6 N2 O2

Cytosine C4 H5 N3 O

Uracil C4 H4 N2 O2

Question 3

Why is DNA replications describes as semi conservative

Answer 3

Strands from original DNA molecule acts as templates

New DNA molecule contains 1 old strand and 1 new strand (specific base pairing enables genetic material to be conserved accurately)

Question 4

Explain the role of helicase in semi conservative replication

Answer 4

Breaks H-bonds between base pairs to form 2 single strands each of which can act as a template

Question 5

How is a new strand formed during semi conservative replication

Answer 5

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

Question 6

Outline the process of transcription

Answer 6

1. RNA polymerase binds to promoter region on a gene
2. Section of DNA uncoils into 2 strands with exposed bases. Antisense strand acts as template
3. Free nucleotides are attracted to their complementary bases
4. RNA polymerase joins adjacent nucleotides to form phosphodiester bonds

Question 7

Outline the process of translation

Answer 7

1. Ribosome moved along mRNA until start codon
2. tRNA anticodon attaches to complementary bases on mRNA
3. Condensation reactions between amino acids on tRNA from peptide bonds. Requires energy from ATP hydrolysis
4. Process continues to form polypeptide chain until stop codon is reached

Question 8

What happens after a strand of mRNA is transcribed

Answer 8

RNA polymerase detaches at terminator region
H bonds reform and DNA rewinds
Splicing removes introns from pre-mRNA in eukaryotic cells
mRNA moves out of nucleus via nuclear pore and attaches to ribosome