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CBG Period 1 > DNA Structure + Replication (Lecture 2.1) > Flashcards

DNA Structure + Replication (Lecture 2.1) Flashcards

1
Q

Which cells do not have nuclei + DNA

A

Red Blood Cells

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2
Q

What is in the Nucleosome core

A

4 Histones packed together

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3
Q

what is a nucleosome

A

made up of Histone octamere + DNA wraps around it + attached to linker dna

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4
Q

what does linker histone enable

A

folding of complex to more compact shape

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5
Q

How is DNA pulled towards Histones

A

Histones slightly positive and dna slightly negative. Attract

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6
Q

what is chromatin

A

refers to all the proteins (histone + non histone) that help organise dna molecule into loops.

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7
Q

what is chromatin

A

refers to all the proteins (histone + non histone) and nuclear DNA that help organise dna molecule into loops.

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8
Q

what does cell nucleus control

A

growth, metabolism + reproduction

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9
Q

what does staining chromosomes show?

A

each chromosome has unique banding pattern + darker bands= denser regions

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10
Q

Function of Chromatin

A

Organise DNA + Protect from damage. Create environment where certain parts of gene can be expressed or regulated

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11
Q

why is replication origin usually A-T rich regions?

A

decreased energy demand to break bonds as they 2 have 2 H bond per pair compared to C-G which is 3 H bond per pair

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12
Q

What polymerase is used to replicate DNA?

A

DNA polymerase 3

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13
Q

What polymerase is used to replicate DNA (prokaryotes)

A

DNA polymerase III

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14
Q

DNA Replication Summary (prokaryotes)

A

-Helicase enzyme break H bond + unzip @ rep origin
-RNA Primase insert RNA primer (3’ OH end) which places the starting sequences of nucleotides
- 3’ OH end mean DNA Polymerase can attach DNTP in 5’-3’ direction
-@ lagging strand primers are added into okazaki gaps and process repeats
-Ligase place phosphate groups in gaps within sugar-phosphate backbone and join nucleotides together
-

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15
Q

What directions does DNA Polymerase go?

A

5’-3’. Note that they need a primer as they cant make a new dna strand de novo

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16
Q

what is replication fork

A

Region where DNA is being replicated

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17
Q

What does ‘leading’ strand mean

A

DNA synthesis occurs continuously. No Okazaki fragments as daughter strand going 5’-3’. Move towards replication fork

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18
Q

What does ‘lagging’ strand mean

A

Synthesis occurs not continuously. . This is bcs Polymerase can only go in 5’-3’ direction- and as daughter strand needs to be ANTI PARALLEL to parental strand, DNTPS are added AWAY from replication fork (follow anti parallel rule) hence why fragments exist

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19
Q

does dna polymerase initiate synthesis?

A

NO!!!!!!!! only add to pre-existing sequence of nucleotides x

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20
Q

What causes twisting effect in DNA

A

H Bonds

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21
Q

where does the energy for dna synthesis come from?

A

Hyrdrolysis of subsequent PPi to become a phosphate group drives polymerising activity forwards

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22
Q

What were the 3 theories on how DNA replicates?

A

Semi Conservative- Accepted one. Where both strands of original DNA act as single stranded templates separately. Daughter strand therefore has 1 parental and 1 newly synthesised strand
Conservative Replication- Rejected. Where original dna act as DOUBLE STRANDED template to produce wholly new daughter dna
Dispersive- Rejected. Daughter DNA will have alternating segments of parental + newly synthesised interspersed within each strand of DNA

23
Q

Which experiment proved the semi conservative theory as true?

A

Meselson + Stahl exp. ( revise the details in notes)

24
Q

What 3 functions does a DNA polymerase complex have?

A

5’-3’ polymerising activity
3’-5’ exonuclease activity
5’3 exonuclease activity

25
Q

what is an exonuclease

A

enzyme that destroy DNA molecule by cleaving away sugar phosphate backbone. Cleaves at END of polynucleotide chain

26
Q

what is an endonuclease

A

cleave away phosphodiester bond WITHIN polynucleotide chain

27
Q

what does ‘processivity’ refer to

A

How many DNTPS can polymerase add to growing strand before it dissociates from template

28
Q

Chief function of DNAP1 (prokaryotes)

A
  • Remove primers and fill in gaps left behind in daughter strand between okazaki fragments
  • DNA repair
  • involved in multiple processes that require short lengths of DNA synthesis
29
Q

Chief function of DNAP3 (Prokaryotes)

A

-chief replicating/ polymerizing enzyme

30
Q

key features of DNAP3

A
  • very accurate
  • high processivity
  • fast af
31
Q

what is the purpose of exonuclease

A
  • Found in DNAP1. Proof reading function via removing incorrectly matched bases. can go back and forth.
  • exonuclease also gets rid of RNA primer that kick start synthesis

Since proof reading activity is slower than polymerisation- it gives time for exonuclease to catch up with polymerising activity + remove incorrect bases.

32
Q

What are the 10 isoforms of linker histones

A

7 somatic: A,B,C,D,E,H1,H1X

3 Germline:Foo,t,LS1

33
Q

what is H1 function

A

Linker Histone

34
Q

what does acetylating histone tails do

A

Chromatin open and dna less condensed as less strongly attracted to histone tail (histone tail went from positive to neutral). DNA is negative.

35
Q

what does deacetylating histone tails do

A

Chromatin closes as histone tails draw in and dna more condensed. (histone tail becomes more positive and dna is negative)

36
Q

what are telomeres

A

cluster of repeated 6 base pairs (TTAGGG) in humans found @ end of chromosome. Protect integrity of extreme ends of chromo. Defects usually due to cancer/age

37
Q

how to telomeres serve to protect chromosome in duplication

A

bcs they are repeats- essential coding dna isnt lost (during dna replication- starting point of strand has gap bcs primer removed so dna polymerase didnt have a pre-existing strand to work on- until telomerase enzyme came in) so next generation of dna molecule isnt lacking integral info for coding proteins

38
Q

How does telomerase enzyme work to maintain the telomere section in chromosome

A

Telomerase enzyme produces complementary RNA sequence to parental strand that contain telomere section Bcs telomere section is a repeat- it moves along parental strand and extends the parental strand along with it. Extends 3’ end

Once overhanging strand long enough, enzyme leaves. RNA primer added to daughter strand and DNAP add nucleotides and Ligase ligates it together.

This means that no piece of dna is therefore lost- dna ends are protected.

39
Q

what is telomerase enzyme an example of

A

reverse transcriptase enzyme; use RNA to make DNA.

40
Q

what is nucleic acid

A

Polymer. Made up of nucleotides (nitrogenous base-glycosidic bond—hexose sugar-phosphodiester bond- phosphate group)

41
Q

how many chromosomes do humans have

A

46 in 23 pairs

42
Q

Why is dna seen as containing polarity

A

has 2 distinct ends- 5’ end with a free phosphate end (-2 charge) and 3’ end with a free OH group (-1 charge)

43
Q

What are the PURINES

A

two ringed- A + G

44
Q

What are the PYRIMIDINES

A

one ring C + T + U

45
Q

How many H bonds in AT/AU

A

2

46
Q

How many H bonds in CG

A

3

47
Q

Function of Major groove in DNA

A

DNA more accessible therefore more space for protein to bind onto DNA

48
Q

How many purINES can be found in a stretch of 100 bp dsDNA

A
  1. Every pyrimidine is paired up with a purine
49
Q

what is the convention in writing out a sequence of DNA

A

Always start from 5’-3’ (5’=Phosphate end 3’=OH end)

5’GGGA’3 complimentary sequence is 5’TCCC3’

50
Q

why is dna packaging important

A

dna fragile + has info to produce proteins with specific functions to perform chem reactions of life. bcs dna long af- compact shape= take less space up

51
Q

why are nucleosides used to deliver drugs in body

A

nucleoside= base + sugar

because no phosphate group, no 2- charge. molecules with charge are harder to pass thru bilayer. Bcs nucleoside has no phosphate group=less charge= easier to get into cell thru bilayer

52
Q

what are nucleoside analogues

A

synthetic chemically modified block cell division + viral repliction via enzymes or impairing DNA/RNA Synthesis

53
Q

how can you terminate dna synthesis

A

if pre-existing nucleotide does not have a 3’ OH end :)

CBG Period 1 (3 decks)

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