Errors Involving DNA Flashcards by Mira Chainrai

What are oncogenes?

Genes that increase growth, promotes survival and inhibit apoptosis

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Why might oncogenes have an increase in activity?

Due to mutation (either in the gene itself, in other involved signalling proteins or in the transcription factor binding region).

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What are tumour suppressing genes?

Genes that inhibit proliferation, reduce growth or promote apoptosis

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What is the p53 gene?

A tumour suppressing gene that is commonly mutated

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What is slippage in DNA replication?

Where a newly synthesised nucleotide/strand can slip out and so there are extra nucleotides on the strand. Or nucleotides can slip out on the template strand, shortening the DNA strand.

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What is mis-match pairing?

When DNA polymerase inserts the wrong nucleotide

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How can a mismatch be easily repaired?

There can be a base excision repair from the exonuclease domain of the DNA polymerase.

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What results from an increase of p53 activity?

Tumours

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What is DNA replication stress?

Inefficient replication that leads to the replication fork slowing, stalling or breaking

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What happens when the replication fork meets a single strand break?

A double strand break occurs

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What disease results from a trinucleotide repeat?

Huntingtons

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What is dysplasia?

Features of abnormal cell growth

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Errors in what 4 areas lead to genomic instability?

Errors in oncogenes
Errors in tumour suppressing genes
Errors in chromosome structure
Errors in chromosome number

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Increasing the activity of which genes results in dysplasia

Oncogenes

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What is mismatch repair?

When DNA polymerase finds a mistake and so the exonuclease domain cuts out the mistake for polymerase to fix

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Outline nucleotide excision repair

A stretch of damaged DNA is removed by endonuclease and replaced by DNA polymerase and joined together by DNA ligase, using a variety of proteins which are produced in the genes controlling this repair

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What does UV light do to cells?

It initiates a reaction between 2 thymine molecule to form a pyrimidine dimer.

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Why can some DNA synthesis inhibitors be used as antibiotics?

They may only inhibit bacterial DNA synthesis not human

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What is non-homologous end joining used to repair

Double stranded breaks

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Outline non-homologous end joining

The ends are directly lighted. This is done by proteins binding onto the ends of the breaks, which then recruit other proteins which removed damaged strands and then DNA ligase brings the strands together

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What are chromosomal translocations?

When part of a chromosome attaches to another. It can be balanced or unbalanced

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What is chromosomal inversion?

When a segment of DNA is reversed end to end.

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What type of disease can be caused by translocations

Leukaemia

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What is a mutation

An alteration in a gene or chromosome

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What is a bulky addict

When chemicals bind to areas of DNA and prevent it replicating

When do mutations occur

When DNA repair mechanisms are defective

State exogenous sources of mutation

Ionising radiation, free radical, mutagenic chemicals

What are free radicals

Molecules with an extra electron

State endogenous sources of mutation

DNA replication defects and transposable elements

What are transposable elements

When DNA has no fixed position and move around the genome

What happens when a transposable element is inserted into a gene

It deactivates the gene

What is a mircomitation

Mutation involving one or few nucleotides

What is a macromutation

Mutation on chromosomes

What types of micromutations are there?

Deletions, insertions, substitutions

What types of macromutations are there

Deletion, duplication, inversion, substitution and translocation

What do deletions and insertions result in

Frameshift

What are missense mutations

Mutations resulting in a change in amino acid

What are silent mutations

Genes that give no change in amino acid

What is a nonsense mutation

Mutation resulting in an early stop codon

What types of mutations affect the amount of gene product

Mutations affecting translation or transcription

How may mutations affecting splicing affect gene product

Mutations at the end of intron mean splicing sequences change so exams aren't removed. The change in length makes non functional proteins

How does nitrous acid mutate DNA

It changes cytosine to uracil

What is a transition mutation

When a purine is changed to a purine or a pyrimidine changed to a pyrimidine

What is a transversion mutation

When a purine is changed to a pyrimidine

What cells do germ line mutations effect

Sperm and egg

Why do rna errors occur often

RNA Polymerase don't proofread

Why are mutations in rna often not harmful

RNA degrades quickly not passed on and the cell makes multiple copies o DNA

What organs are badly affected by mutations in mitochondria

Organs requiring lots of energy e.g heart, brain and muscle

From whom do you inherit your mitochondria from

Your mother

What results in aneuploidy

Nondisjunction

What is anaphase lag

When chromosomes aren't separated properly during anaphase

Are are monosomy cells not usually found

As they are fatal and result in death

What are primordial germ cells

Cells which develop into sperm and ovum

What is the significance of large amounts of division of germ cells

Lots of chance for mutation

Why does mutation rate of gametes increase with age

More exposure to mutagens/radiation

What is teratogensis

The process by which mutations are produced in an embryo

What do recessive mutations cause

Loss of function

What do dominant mutations occur

Increased function

What is cytogenetics

Study and analysis of chromosomes

What constitutional Abnormalities result in referral for cytogenetic analysis

Prenatal diagnosis, birth defect, infertility and reoccurring fetal loss

What acquired Abnormalities result in referral for cytogenetic analysis

Leukaemia, tumours and specific translocations

What 2 types of prenatal diagnosis methods are there

Chorionic villus and amnioticentesis

What is chorionic villus

Inserting a needle to collect some chorionic fluid which surrounds the placenta using ultrasound

What is amniocentesis

Collecting amniotic fluid using a needle and ultrasound guidance

What is polyploidy

Gain of a whole haploid set of chromosomes

What causes polyploidy

Fertilisation of an egg by more than one sperm

What are the causes aneuploidy

Nondisjunction

What is mosicaism

2 cell populations in an individual

What is Down's syndrome

Trisomy 21

What symptoms are associated with Down's syndrome

Intellectual disability. Heart defects, increased incidents of leukaemia and Alzheimer's

What is the syndrome caused by trisomy 18

Edwards syndrome

What symptoms are associated with Edwards syndrome

Small lower jaw, low set ears, rocker bottom feet and overlapping fingers

What is Patau syndrome

Trisomy 13

What is single X chromosome inactivation

Where only 1 X chromosome is ever active in a human cell

Why is single XChromosome a problem

2 X chromosomes are required to activate genes

What is the name of the syndrome when you only have 1 X chromosome

Turner syndrome

What symptoms are associated with Turner syndrome

Puffy feet,, redundant skin at the back of the neck

What are balanced translocations

Where there is an even exchange of genetic information with no loss of gain

What are unbalanced translocations

Where there is a loss or gain of genetic information

Can microarray detect both balanced and unbalanced translocations

No only unbalanced

What types of segregation result in balanced translocations

Alternate

What types of segregation results in unbalanced translocations

Adjacent, and nondisjunction

What are Robertsonian translocations

When the q arms of 2 Acrocentric chromosomes fuse together

What diagram is used to assess segregation imbalance

Pachytene diagram

What are terminal deletions/duplications

Ones that occur towards the ends of a chromosome

What are interstitial deletions/deletions

Ones that occur in the chromosome arm

What is uniparental disomy

Presence of homologous chromosomes from one parent

What is the significance of uniparental disomy

It affects imprinting (differential expression of genes depending on parental origin of chromosome)

How is uniparental disomy caused

Trisomy rescue, mitotic error

Why might women with balanced translocations have repeated miscarriages

As the separation of their chromosomes result in unbalanced translocations which aren't viable for life

Are gain of function mutations more likely to be dominant or recessive

Dominant

What genes are mutated to give oncogenes

Proto oncogenes

What is bulky adduct

When chemicals are added to DNA which stop it replicated

How does nitrous acid mutate DNA

Changes cytosine to uracil by replacing an NH2 group