FOUNDATION-GENETICS Flashcards
how is DNA read?
3’ to 5’
how is DNA synthesised?
5’ to 3’
what are chromosomes 1-22 called?
AUTOSOMES
what does chromosome 23 determine?
sex
XX or XY
what are the main enzymes involved in DNA synthesis?
1-topoisomerase enzyme unwinds supercoiled helix DNA
2-Helicase enzyme breaks hydrogen bonds between the base pairs of DNA, creating a replication fork
what happens to the leading strand after DNA strands are separated?
- DNA primase adds an RNA primer to the template to begin the 5’ end of the new strand
- DNA polymerase iii binds to the RNA primer and continues to make the leading strand by adding DNA bases
what happens to the lagging strand after DNA strands have been separated?
-DNA primase adds an RNA primer to the template to begin the 5’ end of the new strand
- DNA Polymerase iii binds to these RNA primers and adds DNA on in chunks
- —>forms Okazaki fragments-which are joined by DNA ligase
what is the job of an exonuclease and how is it involved in the final stage of DNA synthesis?
- an exonuclease will go back to cut out the RNA primers
- DNA will be filled in using DNA polymerase i (particularly on the lagging strand)
what is a telomere?
-repetitive nucleotide sequence at the end of every chromosome
what is the role of a telomere?
- prevent the shortening of chromosomes during replication and maintains stability
- prevents the ends of chromosomes being damaged
what is telomerase?
enzyme that extends the telomere of a chromosome by copying a short template sequence within the RNA component onto chromosome ends
describe the steps of transcription.
- DNA Helicase unzips DNA to expose the template DNA
- RNA polymerase binds to a promoter region
- RNA polymerase adds complimentary RNA nucleotides (U instead of T)
- DNA reads 3’—->5’-therefore pre-mRNA is made 5’—–>3’
- pre-mRNA has its introns cut out using a splicesosome
- mRNA moves from nucelus to ribosome for translation
describe the steps of translation.
- ribosomes are found on the RER
- mRNA is read in triplet codons by the ribosome and tRNA molecules
- AUG is start codon
- small ribsosome sub-unit-matches tRNA anti-codons to mRNA codons
- large sub-units-forms peptide bonds between the newly attached amino acids-condensation reaction
what are post-translational modifications?
-a variety of reactions that changes the structure and therefore function of the proteins made in transcription and translation
what do post-translational modifications increase?
functional diversity of the proteome by the addition of functional groups or proteins, proteolytic cleavage of regulatory subunits, or degradation of entire proteins
what are examples of post-translational modifications?
-acetylation, glycosylation, phosphorylation and proteolytic cleavage
- specific examples
- pre-protein is cleaved to form a mature protein
- pro-insulin is cleaved into active insulin + protein C
what is gene expression?
the process by which genes are made available (on) and unavailable (off) for protein synthesis
what can inhibit transcription?
-methylation of DNA-methyl groups bind to cytosine and is a chemical example of epigenetic modification
what promotes transcription?
- acetylation of histones-acetyl groups unwind chromatin from histones and is a structural example of epigenetic modification
- ubiqitination of histones (less condensed)-makes it easier for enzymes to bind and begin transcription
What does pcr stand for?
polymerase chain reaction
what is pcr and what is it used for?
technique used to make copies of a specific DNA region in vitro (in a test tube rather than organism)
-used for-DNA cloning, medical diagnostics and forensic analysis of DNA
what is the goal of pcr?
to make enough of the target DNA region so that it can be analysed
what does pcr require?
a DNA polymerase enzyme that makes new strands of DNA using existing strands as templates
which DNA polymerase is used for pcr and what does it require?
Taq polymerase
-but can only make DNA if its given a primer
what is sanger gene sequencing?
the average of many long molecules with little to no prior knowledge of DNA sequence
Sanger sequencing is a method of DNA sequencing that involves electrophoresis and is based on the random incorporation of chain-terminating dideoxynucleotides by DNA polymerase during in vitro DNA replication
what is NeXT Gen DNA?
individual short molecules, prior knowledge of DNA sequence
a type of DNA sequencing technology that uses parallel sequencing of multiple small fragments of DNA to determine sequence
What are some examples of numerical chromosomal abnormalities (4)?
- aneuploidy
- monosomy
- trisomy
- polyploidy
describe what is meant by aneuploidy.
-a numerical chromosomal abnormality that affects one pair of chromosomes
describe what is meant by monosomy.
loss of one chromosome
describe what is meant by trisomy and give an example of a disorder caused by this.
gain of 1 chromosome eg downs syndrome-Trisomy 21
describe what is meant by polyploidy.
a numerical chromosomal abnormality in which an entire set of chromosomes has been added eg. -triploidy -tetraploidy (fatal)
what are some examples of structural chromosomal abnormalities?
- depletion-section of DNA is deleted
- duplication-section of DNA is duplicated
- inversion-section of DNA is copied the wrong way around
- substitution-section of DNA moves from one chromosome to another
- translocation-2 separate sections of DNA from different chromosomes swap places with each other
what are mendelian genetics?
the manner by which genes and traits are passed from parents to their children
what is autosomal dominance? Give an example of a disorder showing this.
only one copy of an allele is required for expression of gene
Huntingtons
what is autosomal recessive? give an example of a disorder showing this.
2 copies of same allele are required for gene expression of the phenotype
-sickle cell anaemia
what is x-linked recessive and who does it tend to affect?
allele on the X chromosome
tends to affect males predominantly
what is x-linked dominant?
who does it affect?
Is it common or rare?
only 1 copy of allele on X chromosome needed for susceptibility
- affects both males and female but males carry 1 copy of X chromosome-so have higher incidence and severity
- RARE
what is co dominance and what is an example?
alleles are equally expressed, leading to both phenotypes being present
eg-maternal blood type A, paternal B
offspring blood type AB
what is penetrance?
the proportion of people with a particular genetic change who exhibit signs and symptoms of a genetic disorder
what is incomplete penetrance?
Give an example.
genotype or mutation is present but the phenotype may not be
eg. BCRA1 or BCRA2 gene mutation may not necessarily cause cancer
what is lyonisation?
females inherit 2 X chromosomes of which one X chromosome is inactivated randomly and permanently-this is to prevent over expression of genes
what is mitochondrial DNA?
DNA plasmids exist in the mitochondria and this always comes from the mothers ovum
what are features of autosomal dominant pedigree diagrams?
-doesn’t skip a generation
-proportion seen in males equal to proportion seen in females
-typically associated in conditions where there is an overproduction of protein
eg huntingtons
what are features of autosomal recessive pedigree diagrams?
-affects males and females proportionally
-tends to skip a generation
-lack of function of an enzyme is likely to be autosomal recessive
eg sickle cell anaemia
what are the features of x-linked recessive pedigree diagrams?
- predominantly present in males passed over from the mother who is a carrier
- this is because only 1 X chromosome is present in a male and this will only come from the mother
- daughters are less likely to get it as they would require 2 defective alleles from mother and father
outline the steps of PCR
1-denaturation
–>addition of heat (94-98 degrees) to separate DNA stands
2-annealing
- ->cooling strands (45-60 degrees)
- ->primers join to strands at specific segment of DNA you want amplified
3-dna synthesis
- ->dna polymerase works on the 2 strands adding DNA nucleotides
- ->increased temp to 70-75 for taq polymerase to work optimally
