lecture 3

Question 1

proofreading and repair of DNA

Answer 1

• polymerase proofreads; replacing incorrect nucleotides
• DNA damaged by chemicals/radiation errors corrected by mismatch repair DNA
• excision repair: nucleotide cuts damage stretches replaced by polymerase; end joined by ligase)
• uncorrected eroors become permanent mutations

Question 2

replicationg ends of DNA molecules

Answer 2

• polymerase requires 3’ end to initiate elongation
• machinery provides no way to complete 5’ ends (repeated rounds of replication produce shorter DNA molecules)

Question 3

telomeres

Answer 3

• chromosomes shorten with age
• eukaryotic chromosomal DNA have short ends repeated (telomeres)
• do not prevent shortening; postpone erosion of genes near ends
• germ cells; telomerase catalyses lengthening of telomeres

Question 4

bacterial chromosomes

Answer 4

• double stranded circular molecule genome
• proteins cause DNA coil to supercoil (denser) in unbound region (nucleiod)
• additional plasmids (circular DNA) carry additional genes (may resist anitbiotics)

Question 5

eukaryotic chromosomes

Answer 5

• genome made of true chromosomes (double-stranded; linear DNA association with proteins-histones; coiled and supercoiled chromatin
• located in nucleus

Question 6

chromosome dynamics

Answer 6

• dynamic structures (change during cell cycle)
• most chromatin loosely packed in nucelus (euchromatin) before consensing
• interphase: some chromatin remain condensed (heterochromatin) making gene experssion difficult)