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A Level Biology > DNA and Mitosis > Flashcards

DNA and Mitosis Flashcards

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1
Q

What 3 components make up DNA

A

deoxyribose pentose sugar
phosphate group that bonds to the sugar on the next
organic base

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2
Q

What is a purine

A

a double ringed structure

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3
Q

What two bases are purine

A

A, G

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4
Q

What is a pyrimidine

A

a single ringed structure

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5
Q

Name the two bases that are pyrimidine

A

T, C

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6
Q

What reaction joins nucleotides

A

condensation

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7
Q

What bond does this create

A

phosphodiester

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8
Q

How many hydrogen bonds does thymine and adenine create

A

2

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9
Q

How many hydrogen bonds does guanine and cytosine create

A

3

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10
Q

When replicating DNA, where does it start

A

at the 5 prime down to the 3 prime

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11
Q

Is DNA thermally stable

A

yes, it can withstand high temperatures and has rare mutations

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12
Q

What does the rigid phosphodiester backbone do

A

protects the base pairs on the inside of the helix

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13
Q

Why is it beneficial that the hydrogen bonds are easily split by enzymes

A

it allows replication to occur

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14
Q

What happens in the first stage of replication

A

DNA helicase unzips 2 strands by breaking hydrogen bonds

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15
Q

Why does it only unzip 4-5 base pairs at a time

A

to prevent damage

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16
Q

What happens at the second stage of replication

A

the free nucleotides bind, and are activated and attracted to complementary base pairs

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17
Q

What happens in the third stage

A

DNA polymerase joins together nucleotides by covalent bonds to create the backbone

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18
Q

What makes this semi-conservative

A

it ends with two DNA molecules, each with a new synthesised strand and one from the original

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19
Q

Explain conservative replication

A

complete parent molecule acts as a template and is unchanged

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20
Q

Who proved semi-conservative replication

A

Meselohn and Stahl

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21
Q

What did they do

A

grew e coli with different isotopes of nitrogen
exposed it to N15 for several generations then N14
could then distinguish between different DNA densities by centrifuging

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22
Q

When does mitosis occur

A

growth and asexual reproduction

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23
Q

Why is mitosis separated into stages

A

for our convenience

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24
Q

What happens in interphase

A

the cell is metabolically very active
DNA in nucleus doubles
new organelles are made

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25
Q

How do we identify interphase

A

no chromosomes visible

chromatin is spread through the nucleus in a diffuse form

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26
Q

What happens in prophase

A

chromosomes become visible
(centrioles divide and move to the opposite poles
protein microtubules develop from each centriole forming spindle fibres) only animal cells

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27
Q

What phase is the longest

A

prophase

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28
Q

How can we identify prophase

A

each chromosome can be seen to consist of two chromatids held together by a centromere
nucleolus disappears and the envelope breaks down

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29
Q

What happens in metaphase

A

chromosomes line up on the equator

they attach themselves to the spindle by their centromere

30
Q

What happens in anaphase

A

the centromeres divide

free chromatids move to poles due to contraction of spindle fibres as they shorten

31
Q

How do we identify anaphase

A

by < > shape

chromatids separate

32
Q

What happens in telophase

A

chromatids reach the poles
distinct chromosomes
new nuclear envelopes form
chromosomes uncoil into chromatin

33
Q

How do cells in prokaryotes divide

A

binary fission

34
Q

Explain binary fission

A

cell replicates DNA
cytoplasmic membrane elongates separating DNA molecules
cross wall membranes form completely
daughter cells form

35
Q

What is a gene

A

a section of DNA

36
Q

What do genes contain

A

info for making polypeptides and functional RNA

37
Q

Where is a gene

A

specific position on a DNA molecule called a locus

38
Q

How many amino acids are there

A

20

39
Q

What is the maximum number combinations that can be made

A

64 but some are redundant

40
Q

How many triplets code for an amino acid

A

2-6

41
Q

Does the linear code read in multiple ways

A

no, only in one direction

42
Q

What is always the start code

A

metnionine

43
Q

What happens to this is it is not part of the polypeptide

A

it may be removed

44
Q

What are exons

A

expressed genes that are coding

45
Q

What are introns

A

interruptions that are non coding

46
Q

where are these found

A

eukaryotes only

47
Q

What is DNA in chromosomes held by

A

histones

48
Q

What are chromatids

A

individual strands of DNA

49
Q

What is histones only job

A

to keep DNA tightly coiled in a fixed position

50
Q

Are genes in the same loci on each chromosome

A

yes

51
Q

How many chromosomes do we have

A

46

52
Q

What is a mutation

A

changes in the base sequence of a gene

53
Q

Why is messenger RNA used as transport

A

as it is small enough to leave the nucleus

54
Q

The genome includes genes in what

A

mitochondria and chloroplasts

55
Q

Name 4 features of mRNA

A

1000s of mononucleotides
long single strand
helical shape due to phosphate sugar bonding
info in codons

56
Q

What is mRNAs function

A

to associate with ribosomes

sequence of codons determines amino acid sequence

57
Q

Name 5 features of tRNA

A 
single stranded
mononucleotides
clover leaf shape
one extended end 
opposite end has specific anticodon
58
Q

What attaches to the extended end

A

amino acid

59
Q

Where does RNA polymerase bind

A

promoter region

60
Q

Where does RNA polymerase release

A

terminator region

61
Q

What happens in initiation

A

RNA polymerase binds to pr
elongation
termination

62
Q

What is gene expression controlled by

A

allowing or not allowing the binding of RNA polymerase

63
Q

What does mRNA have that needs to be taken into account

A

exons and introns

64
Q

What is added to mRNA to allow it to move through ribosome and so it is read in correct direction

A

5 prime cap and poly-A tail

65
Q

What loops introns and cuts them out

A

spliceosome

66
Q

How many polypeptides does 1 mRNA produce

A

1

67
Q

How many distinct sites does a large ribosomal subunit have

A

3, EPA

68
Q

What site does tRNA go to

A

A

69
Q

What does the E site do

A

expells the amino acid-less tRNA

70
Q

What do stop codons have instead of an anticodon

A

a release factor

A Level Biology (11 decks)

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