Genomics

Question 1

Describe the role of telomerase in cancer cells [3]

Answer 1

1. Extends telomeres to 3’ -OH ends of template DNA
2. Telomeres are non-coding DNA
   » protect essential genes from being eroded as DNA shortens due to ERP
3. Allows cells to divide indefinitely (immortal / no apoptosis)
   * REJECT: uncontrolled CD (stem cell CD is well-regulated)

Question 2

Suggest 2 ways telomerase can be inhibited as a form of cancer therapy [2]

Answer 2

1. asRNA - bind to mRNA template coding for telomerase
2. Competitive inhibitors - block AS of TERT
   » prevent catalysis of formation of PPD bonds
   » prevent elongation of telomeres

Question 3

Describe 2 ways of PTM [2]

Answer 3

1. Activation by biochemical modification
   » glycosylation/phosphorylation/proteolytic cleavage
2. Tag with UBIQUITIN&raquo_space; enter PROTEOSOMES

Question 4

Explain how mature RBCs can regulate the Tsl of the stored mRNAs to prevent wastage of resources [2]

Answer 4

1. TRANSLATIONAL REPRESSOR PROTEIN binds to 5’ UTR

2. Prevents small RS from binding&raquo_space; formation of Tsl IC

Question 5

Discuss if protein glycosylation is influenced by genes expression [2]

Answer 5

NO - genes do not code for oligo

YES - enzymes that mediate glycosylation are coded for by genes

Question 6

Explain how the structure of the centromere allows it to carry out its functions [3]

Answer 6

COMPULSORY POINT 1
» non-coding tandem repeats&raquo_space; specific 3D conformation

2. Allow sister chromatids to bind to each other via kinetochores
3. Allow spindle fibres to bind
   » allow for alignment of chromosomes at the equator during metaphase
   » subsequent separation of sister chromatids to opposite poles

Question 7

State 2 advantages of alternative splicing [2]

Answer 7

1. Increase coding capacity / protein diversity

2. More rapid response to changing environmental conditions / cellular demand

Question 8

Explain the role of rRNA [2]

Answer 8

1. Small RS - bind to mRNA via CBP (A2T, C3G)
2. Large RS
   » bind to aa-tRNAs at P and A site
   » forms peptidyl transferase to catalyse the formation of peptide bonds b/w adjacent AAs

Question 9

Explain how the structure of RNA pol enables it to perform its function [4]

Answer 9

1. AS has a specific 3D conformation that is complementary in shape and charge to DNA template and the incoming nucleotides
   » catalyse the formation of PPD bonds
2. DNA-binding domain has a specific 3D conformation that is complementary to the promoter&raquo_space; initiate Tsc

Question 10

Compare the synthesis of the leading and lagging strand [4]

Answer 10

1. Type of synthesis
   » continuous vs. discontinuous
2. Direction of synthesis
   » towards vs. away from RF
3. Number of primers
4. DNA ligase to seal the nick by catalysing the formation of PPD bonds

Question 11

Suggest why DNA replication is “asymmetrical” [2]

Answer 11

1. DNA POL works in 5’ to 3’, adding dNTPs to 3’ -OH

2. Template strands are antiparallel

Question 12

Explain how Fig 1.1 shows SCR [3]

Answer 12

1. Parental DNA molecule separates into 2 single strands which serve as TEMPLATES
   »> via CBP, A2T C3G
2. 2 daughter molecules each consisting 1 original + 1 newly synthesised

Question 13

Explain the importance of H-bonding in DNA structure [2]

Answer 13

1. Hold strands together to form a DNA molecule
2. Numerous H-bonds&raquo_space; confer stability
3. CBP - A2T, C3G
4. Weak bonds&raquo_space; easily broken for strand separation for SCR/Tsc