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FunMed > Genetics > Flashcards

Genetics Flashcards

1
Q

What makes up a nucleotide?

A

A sugar
A phosphate group
A base

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2
Q

Which bases are purines?

A

Adenine

Guanine

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3
Q

Which bases are Pyrimidines?

A

Cytosine

Thymine

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4
Q

How many bonds are in the complementary base pairs?

A

3 bonds between C and G

2 bonds between A and T

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5
Q

Explain the stages of DNA folding?

A
  • DNA strand
  • Nucleosomes (beads on a string where you have DNA wrapped around a histone core.
Histone cores are made up of 
2 x H2A
2 x H2B
2 x H3
2 x H4

You also have a linker histone at the joint of the nucleosome (the elbow) which is H1

(next usually textbooks say the 30nm chromatin structure but this hasn’t shown to exist in vivo)

  • Interphase chromatin DNA folding which interphase folding factors (x1000)
  • Metaphase folding into chromosomes (x10000)
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6
Q

Direction of DNA strands? And what is on each end?

A

5’ to 3’

5’ end has a free phosphate group
3’ end has a free OH

They run anti parallel

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7
Q

What is the Central dogma of genetics? What direction does it go in?

A

DNA

(Transcription)

RNA

(Translation)

Proteins

It was thought to be fixed and uni-directional but now they know that there are special mRNAs and proteins that affect RNA production

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8
Q

At what stage of the cell cycle is compaction the greatest?

A

Mitosis (x10000)

Interphase is only 1000

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9
Q

How long does Interphase take of the cell cycle?

A

90%

20-24 hours

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10
Q

What are the different stages of The Cell Cycle?

A

G1 - Growth 1

(G1/S checkpoint)

S - Synthesis
G2 - Growth 2

(G2/M checkpoint)

Mitosis

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11
Q

What are the different stages of Mitosis?

A

Prophase - spindles form

Metaphase - chromosomes go to the middle

Anaphase - chromosomes break apart

Teleophase - nuclear envelope forms?

(Cytokinesis - separate into 2 cells)

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12
Q

Name the cells DNA repair mechanisms

A

The first stage is DNA polymerase that edits as it synthesises

The if a mistake is not picked up you have either single strand repair mechanisms or double strand mechanisms

Examples of single strand repair mechanisms are base excision repair, nucleotide excision repair and mismatch repair

Double strand break mechanisms include non homologous end joining and homologous recombination

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13
Q

Name single strand DNA repair mechanisms

A

Base excision repair
Nucleotide excision repair
Mismatch repair

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14
Q

Name some double strand break repair mechanisms

A

Non homologous end joining

Homologous recombination

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15
Q

Explain how base excision repair works

A

Single stranded DNA repair mechanism

  1. An incorrect base is identified (usually a U)
  2. The enzyme Uracil DNA glycosylase which removes the base
  3. The sugar phosphate is also removed
  4. DNA polymerase adds a new base and DNA ligase glues any knicks
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16
Q

Explain how nucleotide excision repair works

A

Single stranded DNA repair
Targets pyrimidine dimers (where C - T are bound horizontally rather than to their complementary bases opposite them)
Forms bulky adducts

  1. Nuclease cuts out 12 base pairs in bacteria and about 20 in mammals (gap on either side of the wrong base)
  2. DNA Helicase unzips the segment and removes it
  3. DNA polymerase and ligase make a new segment
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17
Q

Explain how mismatch repair works

A

It is a single stranded DNA repair mechanism

  1. The MutS/MutL complex binds to the abnormality. When there is a mismatch, there is often a DNA loop that accompanies it.
  2. The MutS binds to the mismatched base
  3. MutL binds to the loop and looks for a nick or break
  4. The complex then removes the strand
  5. DNA polymerase repairs it and makes a new strand

Abnormalities in the MutS/MutL complex found in inherited cancers

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18
Q

Explain how non-homologous end joining works

A

It is a double stranded repair mechanism
In a double stranded break there are often jagged ends
DNA material is LOST in this process

  1. The jagged ends are chopped off
  2. The ends are joined

Can tell when it’s cancer because material is lost and it’s non-homologous end joining

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19
Q

Explain how homologous end joining works

A

Double strand break repair mechanism

  1. The jagged ends from the double strand break are cut off
  2. No material is lost because the DNA is restored as it’s copied from a second chromosome via homologous recombination

Metaphase from a sister chromatid or the chromosome

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20
Q

Give an example of inherited DNA nucleotide excision repair defects and it’s clinical consequences and its phenotype

A

Xeroderma pigmentosum (XP)

Phenotype:
Skin cancer
Cellular UV sensitivity
Neurological abnormalities

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21
Q

Give an example of inherited DNA mismatch repair defects and it’s clinical consequences and its phenotype

A

MutS, MutL

Phenotype:
Colon cancer

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22
Q

Give an example of inherited DNA homologous recombination repair defects and it’s clinical consequences and its phenotype

A

BRCA2

Phenotype:
Breast and ovarian cancer

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23
Q

Which antibiotics interfere with topoisomerases?

A

Fluoroquinolones

Examples 
Nalidixic acid 
Ciproflaxacin
Levoflaxacin 
Gemiflaxacin
24
Q

Give examples of fluroquinolones and explain what they target

A

Nalidixic acid
Ciproflaxacin
Levoflaxacin
Gemiflaxacin

Target topoisomerases

In aerobic gram positive and negative species
Some anaerobic gram negative species
M. tuberculosis

25
Q

Which bacteria do fluoroquinolones work and what do they target?

A

In aerobic gram positive and negative species
Some anaerobic gram negative species
M. tuberculosis

Topoisomerases

26
Q

What does trimethoprim-sulfamethoxazole target?

A

Nucleotide synthesis in aerobic gram positive and gram negative bacteria

27
Q

Which antibiotic targets topoisomerases?

A

Fluoroquinolones

In aerobic gram positive and gram negative species
Some anaerobic gram negative species
M tuberculosis

28
Q

Which antibiotic targets nucleotide synthesis?

A

Trimethoprim-sulfamethoxazole

In aerobic gram positive and gram negative species

29
Q

Why is there a low level of mistakes in the DNA replication process?

A

DNA polymerase edits as it adds bases

  1. Synthesis occurs from 5’ to 3’ on the new strand
  2. Finds a mistake and goes back 3’ to 5’ on the new strand
  3. Chucks out the wrong base
  4. Synthesis continues 5’ to 3’

1st stage of quality control
Separate sites for editing and synthesis

30
Q

What is the function to topoisomerases?

A

The knick the DNA to avoid supercoiling

31
Q

What direction is DNA replication in?

A

5’ and 3’ in the new strand

32
Q

What are coding sequences?

A

Sequences that encode proteins

They constitute 1.6% of the human genome

33
Q

What are non coding sequences? What do they include?

A

Introns and the regions that are between genes (intergenic regions)

Include: control elements, functional RNAs e.g. microRNAs and long non-coding RNAs

34
Q

What are exons?

A

Regions of genes that encode protein sequences

35
Q

What are introns?

A

Non coding regions between exons in genes

36
Q

What are control elements?

A

Sequences such as promoters and enhancers that regulate transcription

37
Q

What is a pseudogene?

A

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

38
Q

What are repetitive sequences?

How much of the genome does it take up?

A

Tandem repeats of closely related DNA sequences

40% of the genome

39
Q

What does aneuploidy mean?

A

Abnormal chromosome number

40
Q

What does polyploidy mean? Give examples

A

Gain of one or more haploid chromosome sets

E.g. Triploid (3 haploid sets)
Tetraploid (4 haploid sets)

41
Q

What does monosomy mean?

A

One copy of the chromosome

42
Q

What does trisomy mean?

A

3 copies of the chromosome

43
Q

What does tetrasomy mean?

A

4 copies of the chromosome

44
Q

What does disomy mean?

A

2 copies of a chromosome

Normal

45
Q

What is the haploid chromosome number?

A

23

46
Q

What is the diploid chromosome number?

A

46

47
Q

What is a translocation?

A

Joining of part of one chromosome to a second chromosome

48
Q

What is a reciprocal/balanced translocation?

A

Part of the second chromosome joins the first chromosome and there is no net loss or gain of material

49
Q

What is a Robertsonian translocation?

A

Two chromosomes joining at their centromeres

50
Q

Name some examples of common numerical abnormalities in liveborn babies in the autosomes

A

Down syndrome
Edwards syndrome
Patau syndrome

51
Q

Name some common numerical abnormalities in liveborn babies in the sex chromosomes

A

Turner syndrome

Klinefelter syndrome

52
Q

Name a common numerical abnormality in live born babies in all the chromosomes

A

Triploidy (69 chromosomes)

53
Q

In which chromosome is there aneuploidy in Downs Syndrome? Name the frequency of the condition and percentage still born.
Name common features and symptoms of individuals

A

Trisomy 21

1 in 700 live births
Over 60% are spontaneously aborted
20% still born

Distinct facial appearance (flat nose, upward slant eyes)
Marked muscle hypotonia (decreased muscle tone) as a baby
Single palmar crease (hand crease)
Learning difficulty (IQ under 50)
Congenital heart malformations (inherited from birth)

54
Q

What are the three patterns of chromosomes that can cause Downs Syndrome? What percentage of sufferers have each?

A
  • 95% have 3 separate copies of chromosome 21
  • 4% have an extra copy of chromosome 21 due to a Robertsonian translocation
  • 1% have a mosaicism with normal and trisomy 21 cell lineages
    Milder features, post zygote
55
Q

How does Down syndrome link with maternal age?

A
  • Trisomies increase when maternal age increases

FunMed (7 decks)

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