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biomedical science > Lecture 1 - DNA > Flashcards

Lecture 1 - DNA Flashcards

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1
Q

what are the components of DNA

A
  • its a nucleic acid
    -a macromolecule made up of 2 polynucleotide chains
  • nucleotides consist of deoxyribose, a nitrogen containing base (adenine, thymine, guanine or cytosine), a phosphate group
  • the base is connected to carbon 1
    -the 3’ carbons hydroxyl group will join to the adjacent nucleotide
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2
Q

what makes up a nucleoside?

A

sugar and base

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3
Q

whats the bond that connects the sugar and base

A

N-glycosidic bond

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4
Q

what do phosphodiester bonds do

A

connect adjacent nucleotides, to create the sugar phosphate backbone

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5
Q

what bond connects the bases of opposite strands and how many of these bonds

A

-hydrogen bonds
-A and T have 2
-C and G have 3

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6
Q

what bases connect with which?

A

adenine and thymine
cytosine and guanine

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7
Q

which bases are pyrimidines and which are purines?

A

-adenine and guanine are purines
-thymine and cytosine are pyrimidines

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8
Q

is DNA a right or left handed helix?

A

right

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9
Q

what is important about the grooves in DNA?

A

-some proteins need to interact with the DNA and the bases and some cases need to pull apart bases and these grooved provide access to the DNA and bases

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10
Q

How do nucleotides join together?

A
  • a condensation reaction, which eliminates water
    -this creates a 3’,5’ phosphodiester bond
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11
Q

why is DNA replication important in cell division?

A

when a cell divides, both daughter cells must receive a complete set of genes, so the DNA molecules (chromosomes) must replicate accurately before division

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12
Q

what happens in asexual reproduction?

A

1- the entire genome is on one circular chromosome = DNA molecule
2-the chromosome replicates once to produce two chromosomes that are identical (except for rare chromosomes)
3-the two identical daughter chromosomes move toward opposite end of the cell
4-when the cell divides the daughter chromosomes are partitioned one to each daughter cell

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13
Q

why does replication need to be accurate?

A

so the daughter cell ends up with two copies of the genome, identical or near identical to the parent

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14
Q

what happens in M phase in the cell cycle?

A

mitosis and cytokinesis

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15
Q

what happens in G1 and G2?

A

transcription of genes

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16
Q

what happens in S phase?

A

it depends where the genes are in the genome and how the replication process is going as to whether transcription can occur in those genes or not

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17
Q

is DNA replication semi-conservative?

A

yes

18
Q

where do each strand come from in DNA replication

A

one from the parent and one is a new strand

19
Q

what strand determines the sequence of the newly synthesised strand

A

the template strand

20
Q

which end of the molecule do the nucleotides add onto

A

3’ end

21
Q

is DNA parallel or anti-parallel?

A

anti-parallel

22
Q

what happens in DNA replication?

A

1-the strands separate
2-a new strand is made using each old strand as a template according to the rules of base pairing

23
Q

what direction does DNA synthesis occur in?

A

5’ to 3’ direction

24
Q

what does helicase do in replication?

A

unwinds double helical DNA, giving all other proteins required access to the template

25
Q

what do single binding proteins do?

A

help maintain single strands of DNA and keep the DNA unwound

26
Q

what does primase do?

A

adds ribonucleoside triphosphates to synthesise an RNA primer

27
Q

differences between RNA and DNA

A

-RNA is single stranded, DNA is double stranded
-RNA has ribose but DNA has deoxyribose
-RNA has uracil instead of thymine

28
Q

can DNA synthesis start on its own

A

no

29
Q

what happens when an RNA primer is added

A

it creates a 3’ end which the DNA polymerase can start adding to

30
Q

what does DNA polymerase do, and what does it require?

A

-it proceeds in a 5’ to 3’ direction
-adds 1000 bases/second to the growing chain
-requires all 4 dNTP’s deoxyribonucleotides
-must have a template and a primer
-has proof reading activity

31
Q

what do exonucleases do?

A

removes nucleotides from the end of the DNA strand; different enzymes work 5’ to 3’ or 3’ to 5’
(removes the RNA primer and then fills the space in with DNA)

32
Q

what does ligase do?

A

ligase joins ends of single DNA strands by making new phosphate bonds

33
Q

what does it mean by DNA polymerase having proof reading activity?

A

it can detect if there are errors and could remove the wrong nucleotide and correct it with the right one

34
Q

Process of DNA replication

A

-DNA is unwound by helicase
-Ssbp bind to the DNA to keep the strands separate
-a replication bubble is where the 2 strands are pulled apart, and then DNA replication will proceed in both directions
-primase lays downs the primer
-DNA polymerase starts adding nucleotides
-DNA polymerase will extend and produce DNA from this 3’ end of this primer
-when the DNA arrives at the RNA primase it needs to be removed and then a polymerase fills in the gap
-the ligase then joins the two pieces together

35
Q

what are origins of replication

A

places in the genome where replication starts

36
Q

what does gyrase do?

A

-gyrase is a topoisomerase
-it relaxes supercoils produced when the molecule is twisted during replication
-also facilitates unwinding at beginning of replication

37
Q

what does telomerase do

A

uses a short RNA template to add short DNA repeats to the short ends of linear chromosomes when the last primer is removed using RNA template

38
Q

why is telomerase important

A

protects our chromosomes

39
Q

what happens to telomerase over time and how does it effect the genome

A

it shortens over time and after multiple divisions and this process makes the genome more vulnerable
- exceptions to this are stem cells

40
Q

which enzyme removes supercoiling in the replicating DNA ahead of the replication fork?

A

topoisomerase

biomedical science (8 decks)

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