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Flashcards in Molecular Biology and Genetics Deck (80):
1

What's the difference between purines and pyrimidines?

Purines are the larger molecules

2

Which nitrogenous bases are purines and which are pyrimidines?

Purines: A and G
Pyrimidines: T and C

3

How many hydrogen bonds are there between G-C and A-T?

G-C = 3 H bonds
A-T = 2 H bonds

4

Define 'nucleotide'

Sugar, phosphate and nitrogenous base

5

What is present at the 3' end of DNA?

-OH (hydroxyl) group

6

What is present at the 5' end of DNA?

Phosphate group

7

In which direction does DNA replication occur?

5' to 3'

8

What is the role of topoisomerase?

Prevents supercoiling of DNA

9

How does the antibiotic quinolone work?

Targets topoisomerase to cause supercoiling and double strand breakage

10

In which direction does DNA editing occur?

3' to 5'

11

Name the 3 ways of repairing single strand DNA defects

Base excision repair, nucleotide excision repair and mismatch repair

12

Name the 2 ways of repairing double strand DNA defects

Non-homologous end joining and homologous recombination

13

Describe base excision repair

Removal of incorrect base using [BASE] DNA glycosylase enzyme to break phosphodiester bond, then DNA polymerase will insert new nucleotide and DNA ligase will seal

14

Describe nucleotide excision repair

Dimer forms between two base pairs, nuclease then cleaves ~12 phosphodiester bonds, DNA helicase then unwinds section and allows complementary base pairing again, DNA polymerase facilitates, DNA ligase seals backbone

15

Describe mismatch repair

If there is an error in a newly made strand then mismatch proofreading proteins bind (MutS binds to mismatched base pair, MutL scans nearby DNA for nicks and triggers strand removal up to mismatch point), this is followed by DNA synthesis once more

16

Describe non-homologous end joining

Accidental breakage of DNA strand followed by further loss of nucleotides from end degradation, then the ends rejoin in the absence of nucleotide portion (abnormal)

17

Describe homologous recombination

Accidental breakage of DNA strand followed by further loss of nucleotides from end degradation, then nucleotide structure is copied from a second chromosome in order to fill in gap of missing nucleotides prior to end re-joining

18

What are the consequences of a defect in xeroderma pigmentosum?

It affects nucleotide excision repair and increases likelihood of skin cancer and increases UV sensitivity

19

What are the consequences of defects in MutS or MutL?

This affects mismatch repair and increases likelihood of colon cancer

20

What are the consequences of a defect in BRCA2?

Affects homologous recombination repair, and increases likelihood of getting breast/ovarian cancer

21

Describe the mitochondrial genome

Has 13 protein coding genes on 1 circular DNA molecule and this DNA is inherited from the mother

22

Define 'autosomes'

Chromosomes which aren't sex chromosomes, therefore 1-22

23

Define 'karyotype'

Number and appearance of chromosomes in the nucleus of cell

24

Outline the structure of a chromosome

Top is the p (short) arm, the bottom is the q (long) arm, the tips are coated by telomeres which is a 'protein cap' of repetitive DNA. In the middle of the top body is the G light band, and at the bottom middle is the G dark band, and in the middle is the centromere

25

What is the G light band?

A gene rich, G and C dense, early replicating part of chomosome

26

What is the G dark band?

A gene poor, A and T rich, late replicating part of the chromosome

27

Define 'aneuploidy'

Abnormal chromosome number

28

Define 'exon'

Region of gene that encodes protein sequences

29

Define 'intron'

Non-coding regions of DNA between exons in genes

30

What are genetic 'control elements'?

Sequences such as promoters and enhancers that regulate transcription

31

What is a pseudogene?

A non-functional copy of a gene that arises from gene duplication followed by a deleterious mutation in one copy

32

What happens to intron regions after transcription?

There is splicing to remove them and leave only the exons

33

Describe 'robertsonian translocation'

The joining of two chromosomes at the centromere (vertically)

34

Outline Down Syndrome

Trisomy of chromosome 21 --> muscle hypotonia and congenital heart malformations

35

Outline Edwards Syndrome

Trisomy of chromosome 18 --> multiple malformations including clenched hands with overlapping fingers

36

Outline Patau syndrome

Trisomy of chromosome 13 --> incomplete brain lobation, cleft lip and congenital heart disease

37

Outline Klinefelter syndrome

47 chromosomes, having XXY (affects males) and leads to infertility, lack of testosterone and tallness

38

Outline Turner syndrome

45 chromosomes, just X (females) --> infertility, short stature and webbed neck (excess skin)

39

When do females experience X chromosome inactivation?

Early in embryonic development

40

Describe X inactivation in women

X inactive specific transcript (Xist) is a long non-coding piece of RNA in the X-inactivation centre on the X chromosome, and this works to associate closely with the chromosome in order to cause changes to the chromatin and special reorganisation of the chromosome to cause transcriptional inactivation

41

Describe the role of Y chromosomes in male sex differentiation

SRY region of Y chromosome (sex-determining region of Y chromosome), which then encodes proteins of the HMG group of transcription facotrs

42

What is different about DNA in B and T cells?

Been rearranged

43

Which RNA polymerase makes rRNA?

Pol I

44

Which RNA polymerase makes tRNA?

Pol III

45

Which RNA polymerase makes mRNA?

Pol II

46

Describe the stages of mRNA synthesis

Initiation - RNA polymerase binds to gene
Elongation - polymerase transcribes gene
Termination - polymerase stops transcribing
Processing - mature mRNA formed
Export - mRNA leaves nucleus to be translated

47

What is the structure and function of the promoter region of genes?

The promoter region lies upstream of the gene exon and acts as template for the preinitiation complex, bringing Pol II to the gene so it can be transcribed

48

What are transcription factors?

DNA binding proteins which either enhance or repress the assembly of the pre-initiation complex

49

Define 'proteome'

the entire set of proteins expressed by a genome, cell, tissue, or organism at a certain time

50

How is immature mRNA processed prior to translation?

Processed by capping, slicing and polyadenylating

51

What do antibiotics target?

Ribosomes

52

In what direction to RNA polymerases work?

5' to 3' direction

53

What is a missense mutation?

A single base change that changes the amino acid coded for

54

What is a nonsense mutation?

Single base change leading to a stop codon

55

What is a splice-site mutation?

Insertion/deletion of nucleotides at which intron splicing takes place, so this will alter the protein

56

What is a silent mutation?

Base change which doesn't affect amino acid coded for

57

What is a frameshift mutation?

Addition of one base which shifts the entire reading frame

58

What is a regulatory mutation?

Mutation on promoter or other element

59

What genetic mutation causes sickle cell disease?

Base pair change of A to T in B-haemoglobin gene

60

What genetic mutation causes cystic fibrosis?

Deletion of CTT nucleotides in CFTR gene

61

What genetic mutation leads to chronic myelogenous leukaemia?

Chromosome 9 and 22 translocations

62

Give some examples of autosomal dominant conditions

Neurofibromatosis, marfan syndrome, Huntington's disease

63

Give some examples of autosomal recessive conditions

Cystic fibrosis, sickle cell disease, thalassaemia

64

Give some examples of X-linked recessive conditions

Haemophilia, colour blindness, DMD

65

Define 'genotype'

Combination of alleles seen in any one person

66

Provide the equations of the Hardy Weinberg principle

p + q = 1
p2 + 2pq + q2 = 1

67

What are the exceptions to the Hardy Weinberg principle?

No inbreeding

68

Describe the structure of tRNA

Has L-shape 3D fold wit one end attached to specific amino acid and other has anti-codon (3 exposed bases)

69

Which enzyme catalyses the attachment of a specific amino acid to tRNA?

aminoacidacyltransferase

70

Why is tRNA required to error check it's amino acid?

Binding site for amino acids is large so smaller molecules may be able to attach, in this case they must be removed

71

What is meant by the 'tRNA wobble'?

That tRNA can pick up different amino acids due to the redundancy of codons,

72

Describe the structure of rRNA

It has two subunits: large and small and mRNA binds to small subunit, and there are two binding sites for tRNA on large subunit

73

What is the start codon?

AUG

74

What is the first amino acid in translation?

Methionine

75

Describe what happens in the elongation phase of mRNA translation

GTPase hydrolyses GTP to provide energy for tRNA binding, and amino acid is joined to existing AA via peptidyl transferase enzyme

76

Describe what happens in the termination phase of mRNA translation

When stop codon is reached, releasing factors 1 and 2 bind to the protein to cause it's release and then GDP and releasing factor 3 bind to the mRNA (in small subunit) where GTP is hydrolysed and RF1,2 and 3 are released as well as GDP

77

Why are the processes of transcription and translation good targets for antibiotics?

These processes are different in eukaryotes to prokaryotes, so won't affect our structures

78

What is 'DNA methylation'?

Gene methylation inactivates genes, and this involves adding methyl group to cytosine site

79

What are 'histone modifications'?

Activating or repressive modifications of histone proteins that associate with the DNA

80

How can bisulfite sequencing be used to study epigenetic modification?

Investigates DNA methylation: add sulfite to genes and those cytosines which aren't methylated (so are active) will be converted to uracil, then PCR is used, converting the uracil to thiamine if they are methylated (so inactive genes will show)