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CELS > Module 2: Molecular Biology & Genetics And Module 3: Human Molecular Genetics > Flashcards

Module 2: Molecular Biology & Genetics And Module 3: Human Molecular Genetics Flashcards

1
Q

Aneuploidy

A

An abnormal number of a particular chromosome

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2
Q

Example of aneuploidy, and what causes it

A

Down syndrome caused by trisomy 21.

Three copies of chromosome 21, caused by failure of chromosomes to separate during meiosis.

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3
Q

Nondisjunction

A

Failure of chromosomes/ chromatids to separate during anaphase of cell division

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4
Q

What does XXY cause?

A

Klinefelter syndrome

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5
Q

What does XO cause?

A

Turner syndrome

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6
Q

Polyploidy

A

Possession of multiple sets of chromosomes

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7
Q

How does polyploidy come about?

A

Gametes contain same number of chromosomes as parent cell (2n). When fertilised, the two gametes produce a tetraploid (2n + 2n = 4n)

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8
Q

Example of a triploid species

A

Bananas

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9
Q

What is a sure cause of infertility? Why?

A

Odd number of chromosome sets. Not all chromosomes will have homologous chromosomes to pair with due to gametes having different chromosome set numbers

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10
Q

What are the four chromosomal aberrations?

A

Deletion
Duplication
Inversion
Translocation

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11
Q

Deletion, and what disease can it cause?

A

Small part of a chromosome is removed

Lejeune syndrome/ cri du chat: deletion of the top of short arm on chromosome five

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12
Q

Duplication

A

One part of a chromosome is repeated

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13
Q

Inversion, and what effect does it have?

A

Part of a chromosome is taken out, then re-added in the reverse order.

Inversion prevents the production of viable zygotes during meiosis, because crossing over results in uneven chromosomes.

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14
Q

Translocation

A

Part of a chromosome is moved to a non homologous chromosome

Can be reciprocal

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15
Q

Philadelphia translocation

A

Ends of chromosomes 9 and 22 are swapped (translocated)

95% of the time this results in myeloid leukaemia

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16
Q

Familial Down syndrome

A

One 14 chromosome and one 21 chromosome are joined in the parent.

A potential gamete, when fertilised, will produce an embryo with three chromosome 21’s.

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17
Q

Why do we inactivate an X chromosome?

A

Because only one X is necessary- females have an extra one.

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18
Q

What does the inactivated X chromosome show up as?

A

Barr body

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19
Q

When is the X chromosome inactivated?

A

After four days- after the cell has divided several times

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20
Q

How is the X chromosome inactivated, and which one is chosen?

A

DNA is packed closer together, and methyl groups are added to prevent enzymes from interacting with it.

Can be from mother or father

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21
Q

Describe the three components of the Central Dogma of Molecular Biology and their roles

A

DNA- information

RNA- messenger

Protein- worker

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22
Q

Which five processes occur in the central dogma of molecular biology?

A 
Transcription
Translation
Reverse transcription
DNA replication
RNA replication
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23
Q

Gene expression

A

Process by which information from a gene is used in the synthesis of a functional gene product

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24
Q

Functional gene product (2)

A

Protein or non-coding RNA

Product of gene expression

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25
Q

What does a gene do?

A

Produces a type of RNA with a specific function

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26
Q

Transcription

A

Synthesis of double-stranded DNA from a single-stranded RNA

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27
Q

Which enzyme catalyses transcription?

A

RNA polymerase

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28
Q

Coding strand

A

The DNA strand containing the information the cell needs

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29
Q

Non-coding strand

A

The strand that doesn’t contain information the cell needs. Is there for replication

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30
Q

Other name for non-coding strand

A

Template strand

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31
Q

In which direction along the template strand does RNA synthesis occur?

A

3’-5’

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32
Q

Three stages of transcription

A

Initiation
Elongation
Termination

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33
Q

Which stage of transcription differs between eukaryotes and prokaryotes?

A

Termination

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34
Q

Where does initiation of transcription start?

A

At the TATA box in the promoter region of the template strand

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35
Q

TATA box

A

A segment of DNA that contains bases T,A,T,A / is AT heavy

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36
Q

How does initiation of transcription start?

A

TATA box allows transcription factors to bind

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37
Q

Transcription factors

A

Proteins that bind to DNA and help bind the RNA polymerase

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38
Q

What is the name of the complex which includes transcriptions factors and RNA polymerase?

A

Transcriptional initiation complex

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39
Q

RNA polymerase function

A

Starts mRNA synthesis, contains hydroxyl group which means it doesn’t need a primer

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40
Q

Elongation (transcription)

A

RNA polymerase continues to synthesise mRNA from template strand in the 5’-3’ direction

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41
Q

Which regions flank the coding sequence in a gene?

A

5’UTR and 3’UTR

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42
Q

UTR

A

Untranslated region

- a region which is copied in transcription but is not translated

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43
Q

Which nucleotide connects to the 5’UTR before translation?

A

5’G cap

A chemically modified guanine nucleotide

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44
Q

5’G cap function

A

Prevents enzymes from degrading mRNA

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45
Q

What connects to the end of the 3’UTR?

A

Poly-A tail

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46
Q

Functions of poly-A tail (2)

A

Prevents enzymes from degrading RNA

Facilitates transport of mRNA from nucleus into cytoplasm, through a nuclear pore

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47
Q

What connects to the 5’UTR before transcription?

A

Promoter region, including TATA box

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48
Q

What changes does the gene undergo after transcription?

A

Promoter region is lost

5’G cap and poly-A tail are added

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49
Q

Which part of the gene makes it through translation?

A

Coding sequence

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50
Q

Introns

A

Non-coding regions

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51
Q

Exons

A

Coding regions

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52
Q

Splicing

A

Process of removing introns and joining exons together in the coding sequence before translation

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53
Q

Before splicing, what kind of RNA exists?

A

Pre-mRNA (precursor)

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54
Q

After splicing, what kind of RNA exists?

A

mRNA (mature)

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55
Q

What is the name of the triplet-based genetic code?

A

Triplet codon hypothesis

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56
Q

How many possible codons are there? How many codons code for amino acids?

A

64

61

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57
Q

UAA UAG UGA are what kind of codons?

A

Stop codons

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58
Q

Start codon

A

AUG

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59
Q

Adaptor molecule between mRNA and amino acid

A

tRNA

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60
Q

Structure of tRNA

A

Single strand of RNA, 70-80 nucleotides in length

Looped and twisted into 3D L-shape

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61
Q

Where does the tRNA connect the amino acid?

A

At the amino acid attachment site

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62
Q

Anticodon-triplet

A

The triplet of bases on a tRNA which base pairs to the mRNA strand

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63
Q

What happens at the amino a acid binding site?

A

An enzyme joins tRNA to an amino acid by using ATP to form a covalent bond

Different enzyme for each amino acid
In general, it’s called aminoacyl-tRNA synthetase

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64
Q

Three stages of translation

A

Initiation
Elongation
Termination

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65
Q

Ribosome structure

A

Small subunit
Large subunit with A P and E sites
- above the P site is the exit tunnel

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66
Q

Locations of ribosomes (2) and where the proteins go

A

Bound to the rER- used within the plasma membrane or exit (exocytosis)

Free in the cytosol - released into the cytosol and used in the cell

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67
Q

Describe initiation (translation)

A

Small subunit meets tRNA molecule carrying methionine

They find and bind to the 5’G cap of the mRNA

They scan along the mRNA until the start AUG codon, where large subunit joins and methionine is carried by P site

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68
Q

Describe elongation (translation)

A

A charged tRNA arrives at the A site of the large subunit

Simultaneously:

  • amino acid at P site attaches to new amino acid at A site- forming peptide bond
  • ribosome moves along mRNA, shifting positions of the tRNAs so the growing polypeptide sits in the exit tunnel

Then the uncharged tRNA exits out the E site by detaching from its codon

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69
Q

Charged tRNA

A

tRNA molecule with an amino acid attached

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70
Q

Describe termination (translation)

A

Release factor enters A site once ribosome reaches a stop codon
- breaks bond between P site and final amino acid using water

Polypeptide chain detaches from the tRNA, and both subunits and mRNA dissociate

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71
Q

Genotype

A

Set of genes/ DNA combinations responsible for a particular trait

72
Q

Phenotype

A

Physical expression of a genotype

Defined by what happens at the protein level

73
Q

_____ variation commonly leads to _____ variation

A

Genetic

Phenotypic

74
Q

F1

A

First filial generation

75
Q

F2

A

Second filial generation

76
Q

Monohybrid

A

A cross that is heterozygous with respect to one specific gene

77
Q

What does Mendel’s peas experiment show about how information is inherited?

A

Information is passed on to offspring packaged in particles called genes

78
Q

Test cross

A

Crossing a dominant phenotype with a homozygous recessive genotype to find the genotype of the first one

79
Q

Mendels law of segregation

A

Genes segregate at meiosis so that each gamete contains only one of the two possessed by the parent

(Diploid—> haploid)

80
Q

Mendels law of independent assortment

A

Alleles of different genes assort independently during gamete formation

(Where R or r goes does not determine where Y or y goes)

81
Q

Product rule is for ?

A

Independent events

82
Q

Sun rule is for ?

A

Mutually exclusive events

83
Q

Polymorphism

A

When one gene controls more than one allele

84
Q

Incomplete dominance

A

One allele is partially dominant, so a new phenotype is produced

This is not blending

85
Q

Co-dominance

A

Both phenotypes exist side by side

86
Q

Example of co-dominance

A

AB blood type

87
Q

Polygenic traits

A

Traits that are controlled by groups of genes

88
Q

If you graphed a polygenic trait of the population, what would it look like?

A

Normally distributed

89
Q

How does the environments effect on a phenotype change the variation?

A

It smooths out differences

90
Q

What is the name of a trait which is determined by genes on the X or Y chromosome? Give an example

A

Sex-linked trait

Red-green colour blindness

91
Q

Hemizygous

A

Describes an individual who only has one allele. Often a male, referring to a gene on the X chromosome.

92
Q

Will the sons of a father with red green colour blindness also have this?

A

No- it is a trait on the X chromosome- which fathers do not give to sons

93
Q

Recombinant type

A

A new genotype which wasn’t one of the parents

94
Q

Parental type

A

A genotype of one of the parents

95
Q

How do recombinant types occur?

A

They are a result of crossing over during meiosis, where homologous chromosomes exchange parts of a gene and form chiasmata

96
Q

The smaller the distance between two genes, the _____ the recombination frequency?

A

Smaller

97
Q

Recombination frequency

A

Percentage of gametes expected to be recombinant types

98
Q

centiMorgan cM

A

A unit of recombination (1% = 1cM) used for a genetic map

99
Q

Hardy-Weinberg equation (proportions of alleles)

A

p^2 + 2pq + q^2 = 1

100
Q

If 1 in 2500 people have a rare disease, how is this expressed in p and q terms?

A

q^2 = 1/2500

101
Q

Causes of genetic change in a population (7)

A 
Non-random mating
Random genetic drift
- bottleneck effect
- founder effect
Natural selection
Gene flow or migration
Mutation
102
Q

Two types of non-random mating

A 
Inbreeding
Assortative mating (mating within same phenotype)
103
Q

Random genetic drift

A

A random change in allele frequencies due to sampling error over generations

104
Q

Sampling error

A

Who happens to leave offspring out of a population

105
Q

Which factor will increase random genetic drift?

A

Size of the population (smaller)

106
Q

Bottleneck effect

A

An event causes most of the population to die, and the remaining alleles don’t show as much genetic diversity

107
Q

Founder effect

A

genetic diversity of new population in a new location is limited by the genotypes of the founding organisms

108
Q

Stabilising selection

A

Mean stays the same, variation is reduced

Type of natural selection

109
Q

Directional selection

A

Type of natural selection

Mean changes toward one extreme

110
Q

Disruptive selection

A

Type of natural selection

Favours the two extremes of the population

111
Q

Sexual selection

A

A type of natural selection

Favours the phenotype that attracts females more (or males)

112
Q

Frequency dependent selection

A

Type of natural selection

Favours the rarer phenotype

113
Q

Cline

A

Geographic change in genetic/ phenotypic composition

As location changes, frequency of a genotype changes

114
Q

Comparative genomics

A

Comparing genomes to find what is conserved and what is different between or within species

115
Q

Aligning (sequences)

A

The process of lining sequences up next to each other and marking each point where sequences are the same

116
Q

What might differences in genomes within a species be associated with? (3)

A
  • disease
  • characteristics
  • evolutionary history
117
Q

Which two species are the closest relatives of humans?

A

Chimpanzee and bonobo

118
Q

We share all our genes with chimps. How do we differ genetically?

A

We use the genes in different ways

119
Q

What happens when DNA degrades?

A

It’s sequence changes

120
Q

What can ancient DNA be used for?

A

To determine the relationships of extinct animals

121
Q

Closest relative of modern humans

A

Neanderthal

122
Q

Why are Neanderthal remains good for DNA extraction?

A

They are in cold, sealed caves

123
Q

What types of Neanderthal evidence have been found?

A

Tools, art, jewellery

124
Q

Some people carry Neanderthal DNA. What does this mean?

A

They carry alleles that arose in Neanderthals rather than in modern humans

125
Q

Why do some people carry Neanderthal DNA

A

When homosapiens left Africa, some interbred with Neanderthals

126
Q

What allele does Denisovan contribute to the Tibetan population?

A

One that allows them to handle hypoxia (low oxygen)

127
Q

How can we work out what the function of a gene is?

A

By studying organisms that are mutant for that gene

128
Q

Polydactyly

A

Above average number of fingers or toes

129
Q

What is the role of the gene which causes polydactyly?

A

To prevent polydactyly

The mutant form of this gene is unable to do this, so extra fingers or toes grow

130
Q

Does variation in a gene always affect phenotype?

A

Only sometimes

131
Q

How is mutation linked to variation?

A

Mutation is a subset of variation

132
Q

Do mutations affect fitness?

A

Not all the time

133
Q

Myotonia congenita

A

Inherited condition in which muscles fail to relax after contraction,

Due to defect in the gene which encodes a chloride channel receptor

134
Q

Three functional molecular genetics techniques

A

Genetic screen
Transgenesis
Targeted mutation

135
Q

Genetic screen

A

Mutations are introduced to a gamete by treating them with mutagens

The organism is studied for any changes in phenotype

136
Q

Mutagen example

A

X rays or chemicals

137
Q

What makes a model organism

A

It can be easily raised in a controlled environment (not too large or too long lifespan)

Easy to manipulate genetically

138
Q

Transgenesis

A

Foreign DNA is added from one organism into another (inserted into embryo pronucleus)

DNA code is universal- DNA from one organism can be used in another

139
Q

Transgenesis

A

The gene placed into another organism during transgenesis

140
Q

Novel variant

A

A variation of a gene in an organism which isn’t present in the parents’ genomes

141
Q

Targeted mutation

A

Damage or modify the gene we are interested in to work out its normal function

142
Q

Explain the components of the Cas9- guide RNA complex

A

Cas9 is a protein with active sites that can cut the DNA

It forms a complex with a guide RNA with a complementary sequence that can bind to a target gene

By designing the guide RNA, we can choose which gene is cut by Cas9

143
Q

Explain targeted mutation with CRISPR-Cas9

A

Complex enters nucleus and finds target sequence (complementary to the guide RNA) on the DNA

Cas9 makes a double stranded break in DNA at the target site

DNA enzymes try to repair the cut- resulting in small insertions/ deletions in the gene (no template, causes errors)
- this causes mutated gene

We can provide a specially designed repair template for the enzymes to copy, to create our own gene

144
Q

Two conditions for using targeted mutation to treat genetic disease

A

Targets only the cells or organs affected

Is not a change to the germ line/ doesn’t affect next generation

145
Q

Example of gene editing for genetic disease

A

Sickle cell disease

CRISPR-Cas9 used to break a gene (BCL11A) which shuts down gamma genes at birth

Gamma chains help make haemoglobin

146
Q

Sickle cell disease

A

Red blood cells have sickle shape due to two recessive copies in the HBB gene

147
Q

What is cystic fibrosis caused by?

A

Mutation to gene which encodes a chloride ion channel

148
Q

Pre-implantation genetic diagnosis

A

IVF is used to filter out embryos containing a genetic disease

149
Q

Three parent babies

A

If the faulty gene is on mitochondrial DNA

A donor egg is used- with nucleus destroyed- and parents nucleus is transplanted

Contains donor mitochondrial DNA, and prenatal nuclear DNA

150
Q

How does an embryo begin?

A

As a small number of totipotent cells

151
Q

Toro potent

A

Capable of giving rise to any cell type

152
Q

Is trophectoderm totipotent like other embryonic stem cells?

A

No, it’s pluripotent

153
Q

Pluripotent

A

Capable of giving rise to several (not any) cell types

154
Q

During development, cells become more ____ and less ____

A

Specialised

Flexible

155
Q

What is cell polarisation in an embryo?

A

Cells making right connections with each other

Microvilli develop on outer cells at this stage

156
Q

What do the outer cells of the embryo develop into?

A

Trophectoderm

157
Q

What happens once an embryonic cell’s fate is determined?

A

Certain control genes that code for transcription factors become activated

158
Q

Why is it difficult for a cell to switch to a different cell type once it’s fate has been determined?

A

Once transcription factors are made, they make more, which turn on certain genes to transcribe mRNA for cell-specific proteins

159
Q

What does it mean for a cell to be terminally differentiated?

A

It has developed into its cell type, fully functioning in the body

160
Q

Genomic equivalence

A

The theory that all types of differentiated cells contain all the DNA required to build an entire new organism

(All cells contain full genome)

161
Q

Is it easier or harder to create a new cell from the nucleus of a fully differentiated cell than from a less differentiated cell?

A

Harder - but still possible because of genomic equivalence

162
Q

Where can we get embryonic stem cells? They are ____potent

A

Harvested from the inner cell mass of mammalian blastocyst embryos

Pluripotent

163
Q

How are iPS cells made? They are ____potent

A

Induced pluripotent stem cells are made by reprogramming adult skin cells

Pluripotent

164
Q

Adult tissue stem cells are ___potent cells

A

Multi potent

They can divide without limit

165
Q

Umbilical cord stem cells are ___potent

A

Multi potent

Stem cells are isolated from blood of umbilical cord, and frozen

166
Q

Why are umbilical cord stem cells less restricted than adult blood stem cells?

A

They are younger and immature (less differentiated)

167
Q

What disease can umbilical cord stem cells be used to treat?

A

Leukaemia- where affected cells are somatic

168
Q

What are stem cells in our bodies important for?

A

Constant renewal of tissues such as skin and blood

169
Q

Haematopoietic stem cells

Where are they found?

A

Blood stem cells

In the bone marrow

170
Q

Three examples of adult stem cells

A

Fat, bone and white blood cells

171
Q

A fertilised egg is ___potent

A

Totipotent (can give rise to all cell types)

172
Q

What separates totipotent, multi potent and pluripotent cells?

A

Totipotent cells can divide to create an entire organism- including placenta and embryo

Pluripotent cells can divide into all cell types within an organism, but can’t create an entire organism on their own (like totipotent cells can)

Multi potent cells can differentiate into different cell types, but not all

173
Q

What is used to persuade stem cells to develop into different kinds of cells?

A

Different culture conditions

174
Q

How do we use a virus to correct single gene disorders?

A

RNA containing the normal allele is inserted into virus (viral RNA)

Virus infects bone marrow cells that have been removed from patient

Viral DNA carrying the normal allele inserts into chromosome

Engineered bone marrow cells are injected into patient

175
Q

Regenerative medicine is based on the idea that _____

A

Pluripotent stem cells can be used to repair or replace damaged tissues or organs

CELS (3 decks)

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