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2nd yearMedical Genetics > Topic 1 - Cellular and Molecular Basis of Inheritance > Flashcards

Topic 1 - Cellular and Molecular Basis of Inheritance Flashcards

Revise and refresh ¥ DNA, packaging and chromosomes ¥ Gene structure ¥ DNA to RNA to protein ¥ Genetic variation

1
Q

The beginning of life

A

Sperm fertilised egg cell (ovum) to form a zygote.
Ovum and sperm are haploid germ cells.
Zygote is diploid

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2
Q

Heredity

A

early scientists - hereditary characteristics transmitted by proteins.
1944 - bacteria work, DNA responsible

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3
Q

Why was there skepticism by the scientific community about DNA transmitting hereditary characteristics?

A

DNA was considered a very simple molecule - only 4 bases

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4
Q

Structure of hereditary material needed to be:

A

versatile to account for variety.
Be able to reproduce to form an identical replica
Structure described by Watson + Crick and Franklin + Wilkins fulfilled these requirements

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5
Q

Deoxyribonucleic acid (DNA)

A
  • twisted double helix

- made up of 4 bases (chemicals)

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6
Q

Adenine and Thymine

A

2 H bonds

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7
Q

Guanine and Cytosine

A

3 H bonds

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8
Q

Bases are attached by

A

2 phosphate backbones

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9
Q

DNA is

A

tightly packed, takes up less space

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10
Q

How many bases in the whole human genome?

A

3.2 billion bases

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11
Q

DNA packaging chromatin =

A

DNA + RNA + protein

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12
Q

Main protein in chromatin are

A

histones

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13
Q

DNA wound around histones to form

A

nucleosomes

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14
Q

Nucleosomes organise into

A

solenoids

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15
Q

Solenoids

A

loop up into structure of chromatin (tightly packaged fibre)

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16
Q

Histones

A

DNA would round 2 each of histones H2A, H2B, H3 and H4

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17
Q

Histones core particles connected by a

A

short stretch of linker DNA, forming a structure resembling beads on a string

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18
Q

Histone 1 is NOT

A

part of the nucleosome bead

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19
Q

Histone 1 =

A

linker histone

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20
Q

Histone 1 binds to the

A

entry/exit sites of DNA on the surface of the nucleosomal core particle and completes the nucleosome

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21
Q

Types of chromatin

A

Euchromatin + heterochromatin

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22
Q

Euchromatin

A

open chromatin, prevalent in parts of the genome that’s being regularly used + in cells that are active in the transcription of many of their genes (active part of the genome)

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23
Q

Heterochromatin

A

condensed form of chromatin made up of tight loops, most abundant in parts of genome not in active expression + cells that are less/not active

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24
Q

Condensed DNA is packaged into

A

chromosomes

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25
Q

Human genome

A

22 autosomes + sex chromosomes

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26
Q

Human chromosome structure

A

2 identical chromatids, each contains 1 DNA molecule, centromere in middle.

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27
Q

Chromosomes vary in size, which is longest?

A

Chromosome 1

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28
Q

Genetic Makeup of Human cells Haploid

A

23 chromosomes: 1 copy of each autosome and 1 sex chromosome (X or Y)

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29
Q

Genetic Makeup of Human cells Diploid

A

46 chromosomes: 2 copies of each autosome 1-22 and 2 sex chromosomes (XX / XY)

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30
Q

Gene ->

A

Basic physical and functional unit of heredity

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31
Q

Gene is made up of

A

DNA, acts as instructions to make proteins

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32
Q

Genes vary in

A

length; few hundred bases - 2.5 million+

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33
Q

How many genes in the human genome?

A

20,000 - 23,000

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34
Q

Less genes in the human genome than expected, why?

A

due to alternative splicing

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35
Q

DNA to RNA to protein

A
  • central dogma of molecular biology
  • DNA to RNA - transcription
  • RNA to protein - Translation
    Each triplet codon codes a specific amino acid
  • non overlapping
  • more than 1 codon per amino acid - degenerate code
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36
Q

Nonsense mediated control

A

?

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37
Q

Transcription

A
  • RNA polymerase binds to a promoter sequence (near beginning of gene - directly/helper proteins)
  • RNA polymerase uses the DNA template strain to make new/complementary RNA molecule (primary RNA)
  • Transcription ends in termination (depends on sequences in RNA, STOP codon)
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38
Q

what is the main transcription enzyme?

A

RNA polymerase

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39
Q

RNA vs DNA

A

RNA - ss, uracil, less stable than DNA

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40
Q

RNA processing: before primary mRNA molecule leaves the nucles it’s modified:

A

Splicing (removing introns)
Capping (5’ end)
Polyadenylation (3’ end)

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41
Q

RNA capping

A
  • 5’ cap added to 5’ end of newly synthesised mRNA using modified nucleotide 7-methylguanosine (to protect from degradation)
  • capping occur after initiation of synthesis of mRNA and precedes other modifications that protect mRNA from degradation by RNases
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42
Q

closer look at 3’UTR

A
  • 3’UTR begins at Translation Termination Codon
  • part of mRNA and signals end of translation of the nucleotide code into a protein
  • Polyadenylation of 3’ end occur before mRNA leaves nucleus
  • 100-200 nucleotides long, protects mRNA from degradatory action of phasphatases + nucleases
  • Export of mRNA from nucleus into cytosol relies on polyadenylation (adding of polyA tails)
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43
Q

Splicing

A
  • Spliceosomal proteins bind to pre-mRNA template (has introns)
  • Intron removed in the form of lariat and 2 exons ligated (spliced out) to make mature mRNA
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44
Q

Spliceosomal proteins

A

U1, U2, U4, U5, U6)

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45
Q

Translation

A
  • mRNA used as template to assemble amino acids to produce polypeptide
  • occurs in cytoplasm within ribosome
  • Initiation - ribosome connects mRNA with the first tRNA so translation can begin
  • Elongation - amino acids brought to ribosome by tRNAs and linked together to form a polypeptide chain
  • Termination - finished polypeptide released to be folded into mature protein
46
Q

CFTR protein

A

goes to surface of cell, insert into membrane and allows chlorides and water in/out of cell

47
Q

Other Nuclear DNA

A

Genes represent less than 2% of total nuclear DNA

48
Q

Other nuclear DNA, rest of the genome is mostly repetitive DNA sequences

A
  • vary from short repeated segments to repeats thousands of bases long, can repeat from a few to several hundred times
  • previously known as junk/garbage DNA
  • Recent evidence shows that this plays role in regulation of gene expression (base change around 10,000 bases away from promoter sequence was discovered to cause disease in a family)
49
Q

Introns (intragenic regions)

A

non coding regions found within genes - few hundred to several thousand bases long + some contain regulatory elements

50
Q

Intergenic regions

A

regions of genome that don’t contain protein coding sequences - between the genes. CAn contain regulatory elements that may be involved in the regulation fo gene expression

51
Q

Mitochondrial DNA

A
  • 16.6 kb circular double stranded DNA molecule (mtDNA)
52
Q

mt DNA codes for

A

37 genes (on this loop of DNA, many to do with electron transfer chain.

  • 2 types of ribosomal RNA
  • 22 transfer RNAs
  • 13 protein subunits for enzymes - cytochrome b + cytochrome oxidase
53
Q

mtDNA genetic code

A

differs slightly from nuclear DNA

54
Q

Mitochondrial DNA encodes

A

genes necessary for optimal mt function

55
Q

Mitochondria inherited almost exclusively from

A

oocyte, leading to maternal pattern of inheritance that characterises many mitochondrial disorders

56
Q

After fertilisation

A
  • rapid cell division leading to adult human with 1x10^14 somatic cells
  • cell division = Mitosis
57
Q

Mitosis

A

2 identical diploid daughter cells formed from single diploid cell

58
Q

Mitosis (somatic cell division

A

Prophase, Metaphase, Anaphase, Telophase

59
Q

Prophase

A
  • chromosome condensation,
  • spindle formed
  • nuclear envelope
  • organelles disappear
60
Q

Metaphase

A
  • chromosomes connect to spindle fibres and align on metaphase plate in centre of cell
61
Q

Anaphase

A
  • centromeres split + chromosomes separate

- Chromosomes move to opposite poles of cell

62
Q

Telophase

A
  • chromosomes form clusters at opposite poles of cell

- Nuclear envelope and organelles reform

63
Q

Cytokinesis

A
  • cytoplasm divides into 2 parts following furrowing of plasma membrane
  • cell divide, gain separate memrbanes and become independent
    2 identical daughter cells formed
64
Q

Reproductive Cell Division - Meiosis

A
  • gametes ready to produce new organism upon fertilisation
  • 2 step division process produces 4 genetically different daughter cells
  • reduction division
  • gametes - haploid cells (single set of 23 chromosomes)
  • Spermatogenesis + Oogenesis
65
Q

Meiosis

66
Q

Meiosis 1

A
  • reduction division, 46->23 chromsomes
  • prophase 1
  • metaphase 1
  • anaphase 1
  • telophase 1
67
Q

Meiosis 2

A
  • equational division, duplicating what you’ve made, so generate 4 different daughter cells
  • metaphase 2
  • anaphase 2
  • telophase 2
68
Q

Introducing variation during meiosis

A

Crossing over, independent assortment and errors in replication

69
Q

Classification of GEnetic variation

A
  • size (large and small scale)
  • DNA structure (substitution, insertion, deletion)
  • Protein structure (Synonymous, non-synonymous)
  • Coding, non-coding
  • Protein function (loss/gain, dominant negative)
70
Q

single gene

A

CF / Huntington disease

71
Q

Chromosomal disorders

A

Down Syndrome

72
Q

Synonymous

A

has changed the amino acid being coded for

73
Q

Non-Synonymous

A

hasn’t changed the amino acid being coded for

74
Q

DNA repair mechanisms and when they go wrong

A
  • if DNA damage occurs in both somatic and germline cells
  • changes in germline cells = heritable defects
  • changes in somatic cells = nonheritable local changes
75
Q

Mutations drive

76
Q

Mutation can be

A

pathogenic (disease)

77
Q

Mutations in the Mismatch repair mechanisms can cause

A

colorectal cancer

78
Q

Crossing over

A
  • Homologues chromosomes exchange genetic material at chiasma (prophase 1)
  • Resultant chromosomes consist of combinations of parts of the chromosomes - genetic variation
79
Q

Independent assortment

A
  • Anaphase 1, centromeres don’t duplicate or divide
  • only 1 member of each pair of chromosomes migrate to each daughter cell (maternal or paternal)
  • paternal and maternal chromosomes are randomly sorted due to independent segregation, so mix of chromosomes different from cell to cell
80
Q

When Meiosis goes wrong

A
  • Turners syndrome XO
  • Down Syndrome Trisomy 21
  • Edward Syndrome Trisomy 18
  • Patau Syndrome Trisomy 13
81
Q

Cell destiny

A
  • zygote will grow by mitosis to 8 cell stage (embryonic stem cell) then they undergo cellular differentiation (nerve, blood, muscle etc)
82
Q

Cell destiny - - all cells have 3 possible destinies all controlled by the cell cycle

A

1 - remain alive and function withought dividing (neurons)
2 - grow and divide (epithelial cells, liver cells)
3 - Die (necrosis or apoptosis)

83
Q

Cell Cycle

A

alternation of cell division (mitosis and cytokinesis) and interphase

84
Q

Interphase

A

G1, S and G2

85
Q

G1

A

synthesis of RNA and proteins (growing)

86
Q

S

A

DNA replication

87
Q

G2

A

DNA repair takes place, cell prepares for mitosis. Cell contains 2 identical copies of each of the 46 chromosomes

88
Q

G0

A

when cell stops dividing for a long time, length o time varies

89
Q

Rapidly dividing (epithelium) G0 =

90
Q

Liver, G0 =

91
Q

Muscle and nuerones

A

do not divide, permanent G0

92
Q

Cell cycle, cells divide in response to

A

internal and external stimuli

93
Q

Checkpoints at

A

G1, S, G2 and M

94
Q

Tumour suppressors

A

act ot inhibit cell proliferation

95
Q

oncogenes

A

act to stimulate cell growth

96
Q

Cyclins and Cyclin Dependent Kinases (CDKs)

A
  • transition between stages triggered by increased phosphorylation activity of specific CDKs
  • CDK activity in turn is regulated by specific cyclin binding as well as multiple intracellular signalling pathways
97
Q

DNA replication - S phase

A
  • DNA helicase unwinds DNA template
  • ss binding proteins stabilise unwound DNA
  • leading strand synthesis in the 5’ to 3’ direction by DNA polymerase
  • Lagging strand, RNA primase adds RNA primer, then extended by DNA polymerase to form Okasaki fragment
  • DNA ligase joins Okasaki fragments to form continuous strained
98
Q

When Cell Cycle Control goes wrong?

A
  • uncontrolled cell division - cancer
99
Q

Due to a series of changes in activity of cell cycle regulators, through mutation of i.e.

A
  • tumour suppressors becoming inactive

- oncogenes becoming over-active

100
Q

Retinoblastoma (eye cancer in children) caused by

A

mutation in tumour suppressor gene RB1

101
Q

Li Fraumeni

A

multi-organ cancer syndrome caused by mutations in the tumour suppressor p53

102
Q

Lung cancers

A

mutation in kras (oncogene)

103
Q

Cell destinies, all cells have 3 possible destinies

A

1 - remain alive + functioning without dividing (neurons)
2 - grow and divide (epithelial, liver cells)
3 - die (necrosis or apoptosis)

104
Q

Cell Death - Apoptosis

A
  • programmed cell death
  • cell suicide
  • triggered by normal, healthy processes in body, almost always normal + beneficial (removing webbing between fingers of babies)
105
Q

Necrosis

A
  • uncontrolled cell death
  • necrosis - cell death triggered by external factors/disease - trauma/infection
  • abnormal and harmful
106
Q

combination of apoptosis and proliferation responsible for

A

shaping tissues and organs in developing embryos

107
Q

apoptosis has a role in the

A

immune system - any ineffective/self-reactive T cells removed through induction of apoptosis

108
Q

Cancer

A

disease often characterized by too little apoptosis

109
Q

too much apoptosis

A

contribute to neurodegenerative diseases - Parkinsons/Alzheimers, progressive loss of neurons

110
Q

Necrosis

A

cell injury results in premature death of cells in living tissue by autolysis

111
Q

Necrosis caused by

A

toxic chemical/physcical events

  • toxins
  • radiations
  • heat
  • trauma
  • lack of oxygen due to blockage of blood flow

2nd yearMedical Genetics (2 decks)

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