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A Level Biology > DNA and Mitosis > Flashcards

DNA and Mitosis Flashcards

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
How do we identify interphase
no chromosomes visible | chromatin is spread through the nucleus in a diffuse form
26
What happens in prophase
chromosomes become visible (centrioles divide and move to the opposite poles protein microtubules develop from each centriole forming spindle fibres) only animal cells
27
What phase is the longest
prophase
28
How can we identify prophase
each chromosome can be seen to consist of two chromatids held together by a centromere nucleolus disappears and the envelope breaks down
29
What happens in metaphase
chromosomes line up on the equator | they attach themselves to the spindle by their centromere
30
What happens in anaphase
the centromeres divide | free chromatids move to poles due to contraction of spindle fibres as they shorten
31
How do we identify anaphase
by < > shape | chromatids separate
32
What happens in telophase
chromatids reach the poles distinct chromosomes new nuclear envelopes form chromosomes uncoil into chromatin
33
How do cells in prokaryotes divide
binary fission
34
Explain binary fission
cell replicates DNA cytoplasmic membrane elongates separating DNA molecules cross wall membranes form completely daughter cells form
35
What is a gene
a section of DNA
36
What do genes contain
info for making polypeptides and functional RNA
37
Where is a gene
specific position on a DNA molecule called a locus
38
How many amino acids are there
20
39
What is the maximum number combinations that can be made
64 but some are redundant
40
How many triplets code for an amino acid
2-6
41
Does the linear code read in multiple ways
no, only in one direction
42
What is always the start code
metnionine
43
What happens to this is it is not part of the polypeptide
it may be removed
44
What are exons
expressed genes that are coding
45
What are introns
interruptions that are non coding
46
where are these found
eukaryotes only
47
What is DNA in chromosomes held by
histones
48
What are chromatids
individual strands of DNA
49
What is histones only job
to keep DNA tightly coiled in a fixed position
50
Are genes in the same loci on each chromosome
yes
51
How many chromosomes do we have
46
52
What is a mutation
changes in the base sequence of a gene
53
Why is messenger RNA used as transport
as it is small enough to leave the nucleus
54
The genome includes genes in what
mitochondria and chloroplasts
55
Name 4 features of mRNA
1000s of mononucleotides long single strand helical shape due to phosphate sugar bonding info in codons
56
What is mRNAs function
to associate with ribosomes | sequence of codons determines amino acid sequence
57
Name 5 features of tRNA
``` single stranded mononucleotides clover leaf shape one extended end opposite end has specific anticodon ```
58
What attaches to the extended end
amino acid
59
Where does RNA polymerase bind
promoter region
60
Where does RNA polymerase release
terminator region
61
What happens in initiation
RNA polymerase binds to pr elongation termination
62
What is gene expression controlled by
allowing or not allowing the binding of RNA polymerase
63
What does mRNA have that needs to be taken into account
exons and introns
64
What is added to mRNA to allow it to move through ribosome and so it is read in correct direction
5 prime cap and poly-A tail
65
What loops introns and cuts them out
spliceosome
66
How many polypeptides does 1 mRNA produce
1
67
How many distinct sites does a large ribosomal subunit have
3, EPA
68
What site does tRNA go to
A
69
What does the E site do
expells the amino acid-less tRNA
70
What do stop codons have instead of an anticodon
a release factor

A Level Biology (11 decks)

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