MCM LO Lecture #2

Question 1

Identify when DNA replication occurs throughout the cell cycle and where throughout the genome in eukaryotes.

Answer 1

DNA replicated during s-phase mitosis in nucleus

Question 2

Describe the chemical reactions catalyzed by DNA polymerase.

Answer 2

Breaks phosphate bond on new nucleotide and uses energy to from new bond

Question 3

Explain semi-conservative replication.

Answer 3

each daughter strand contains an half of the parent strand

Question 4

Recite the action of DNA and RNA polymerases in leading strand and lagging strand synthesis.

Answer 4

start at origin of replication after dna primase adds ran primer they systematically add new bases 5’ to 3’ on the 3’ end. leading strand follows helices/laggind strand from okazaki fragments which are then connected together by dna ligase. RNA polymerase essentially same except uracil instead of thymine

Question 5

List all subunits of the multienzyme complex responsible for replication and describe each enzyme’s function (DNA polymerase, Helicase and single stranded binding proteins, DNA primase, Clamp protein/clamp loader, DNA ligase, RNAse H, Topoisomerases)

Answer 5

DNA Polymerase- adds nucleotides to 3’/proofreads and corrects mistakes
Helicase-unzips double stranded DNA
single stranded binding proteins-connect to unraveled sides to prevent it from coming back together
Clamp protein/clamp loader-binds polymerase and keeps it on
DNA ligase- connects okasaki fragments by catalyzing phoshodiester bond
RNAse H-removes RNA primers from DNA Separates DNA-RNA hybrids
Topoisomerases- relax dna starns so that they can still be unzipped

Question 6

Be able to describe in a step wise fashion how DNA replication occurs.

Answer 6

1. DNA binding proteins from bubble at replication site uses atp
2. DNA helicase binds and continues to unwind/topoisomerase prevents supercoiling/SSB stabilize replication fork prevent it connecting back together
3. DNA primase binds and adds RNA primer
4. DNA polymerase binds and synthesizes onto the 3’ end clamp protein hold it on
5. lagging strand discontiuiosly uses Dna primase to add RNA timers creating okazaki fragments on lag strand
6. RNAse H removes RNA primers ligase connects fragments

Question 7

Describe the process by which the ends of chromosomes are replicated.

Answer 7

Telopmerase adds repeats to parental strand on 3’ end enough that the end is completely copied at the telomere

Question 8

Know the differences between somatic, germ and cancer cells with regards to telomerase activity.

Answer 8

Somatic cells- little telomerase activity
Germ cells- high telomerase activity
Cancer cells- high telomeres activity

Question 9

Describe the molecular pathology associated with Bloom’s syndrome.

Answer 9

Bloom sysdrome is a defect in BLM gene defective BLM protein means less DNA stablizion/defective helicase more errors prone to cancer/short stature developmental issues

Question 10

Define the nucleosome and list the components of the nucleosome.

Answer 10

Nucleosome-made up of two copies of histone proteins H2A H2B, H3, H4 consists of DNA wound around these proteins.

Question 11

Describe the difference between heterochromatin and euchromatin.

Answer 11

Heterochromatin is tightly packed general towards the membrane of the nucleus does not allow for gene transcription.
Euchromatin is loosely packed allowing for transcription to occur contains lots of genes

Question 12

Explain epigenetic inheritance as it refers to histone modification.

Answer 12

acytlyation of histones lead to uncoiling of histone structure
methylation leads to gene silencing