Molecular Biology and Genetic 16-21 Flashcards
Describe the central dogma of molecular biology
DNA transcribed to RNA transcribed to proteins
Describe gene expression
Process by which information from a gene is used in the synthesis of a protein
What is a gene?
Defined sequence of DNA that produces an RNA molecule
What are the features of transcription?
DNA dependent RNA synthesis
Catalysed by RNA polymerase
Forms phosphodiester bonds between ribonucleotides
What are the 3 stages of DNA transcription?
Initiation
Elongation’
Termination
Describe initiation in DNA transcription
Transcription factors bind to TATA box
RNA pol 2 binds forming initiation complex
DNA strands separate and RNA pol 2 starts mRNA synthesis
Describe elongation in DNA transcription
RNA pol 2 uses the template strand and inserts complementary RNA nucleotides.
What protein on the RNA molecule protects the RNA from degradation on the 3’ end?
Poly-A tail
What is the purpose of a g-nucleotide on the RNA?
Protects the 5’ end of the RNA from degradation
What is splicing?
Introns (intervening sequences) are regulatory elements that regulate translation
What is the function of a coding sequence?
Portion of gene’s DNA translated into a protein
What is the function of a promoter?
DNA segment recognised to RNA poly to initiate transcription
What is the function of a UTR?
Untranslated region.
Contain regulatory elements that influence gene expression at transcriptional level
UTR facilitates addition of ends on 3’ and 5’
Often transcribed and not translated
What is the purpose of a 5’ G cap
Prevents mRNA degradation, promotes intron excision and binding site for small ribosomal subunit
What is the function of a Poly-A tail
Prevents mRNA degradation and facilitates export of mRNA from the nucleus to the cytoplasm.
How many different types of amino acids are there?
20
How bases do amino acids have?
3 (triplets)
What is the purpose of tRNA?
It acts as an adaptor.
How is tRNA charged?
An enzyme releases a specific amino acid and the correct tRNA joins them together
Describe translation
Synthesis of proteins by ribosomes using mRNA as instructions.
What are the 3 ribsoome sties?
A (acceptor site)
P (peptide site)
E (exit site)
What is a ribosome made up of?
Proteins and rRNA (ribosomal RNA)
Where are the ribosome located?
Bound to the rER
Free in the cytosol
What are the purposes of ribosomes?
Synthesis proteins in the plasma membrane or in the cytosol
What are the 3 stages of translation?
Initiation
Elongation
Termination
Describe the translational process of initiation
tRNA binds to ribosomal subunit which identifies the 5’ cap and attaches to the mRNA
tRNA moves along the mRNA until it finds the start AUG codon
First methionine positioned in P site
Large ribosomal subunit attaches
Which amino acid is the start codon?
AUG
Describe the process of translational elongation
Charged tRNA with complementary anticodon arrives in the A site.
ribosome moves along so the amino acid chain is on the P site
Empty tRNA moved toward E exit
Cycle is repeated cause the amino acid chain to grow longer and longer
Describe the process of translational termination
When a ribosome reaches a stop codon, a protein release enters the A site
This breaks the bond between the P site and the tRNA causing the amino acid chain to be released.
What is the difference between genes and alleles?
Alleles are different forms of a gene.
What is the ratio of offspring in a true monohybrid cross?
3:1 ratio in F2 generation
What is the ratio of offspring in a true hybrid cross?
9:3:3:1
What is Mendel’s first law (law of segregation)
Genes segregate at meiosis so that each gamete contains only one of the two possessed by the parent
What is Mendel’s 2nd Law (independent assortment)
Alleles of different genes assort independently during gamete formation
What is the difference between a genotype and a phenotype?
Phenotype is what something looks like and a genotype is a combination of alleles that make it up
How can we calculate the probability of getting a specific genotype?
Sum rule.
a and b are mutually exclusive
Describe incomplete dominance
Blending of 2 genes. 1 gene (Aa) is not enough to be sufficiently dominant
How many what ratio do you get if you mix 2 incompletely dominant phenotypes?
1:2:1
Describe Co-dominance
When both genes are equally expressed, neither is dominant over the other
What is polymorphic?
When there is many alleles for one gene
What is a polygenic trait?
Phenotype that is controlled by many genes that have an additive effect (continuous or quantitive) e.g. skin colour
How can the environment effect phenotypes?
Nutrition = height/weight etc
Describe Sex-linked traits?
Involving genes on the sex chromosomes (X and Y)
Inheritance patterns differ between males and females
Describe how X-linked traits occur
They are recessive and carried on the X chromosome. A mother passes 1 X to her son and a father passes 1 Y. If there is an X-linked gene from the mother, the son will possess it because there is nothing to balance it out
Can a father pass down an X-linked trait?
Yes, but only to daughters, who will have a normal phenotype but be carriers
What happens when a carrier mates with a normal male? in X-linked
Carrier will pass the mutation to half her daughters and half her sons, the sons will have the disorder.
What happens when a carrier mates a male with the trait? X-linked
There is a 50% chance that each child will have the trait
How many genes are there in human?
20,000
Hoe many chromosomes are there in humans?
23 pairs
True or false: vg recessive to vg+?
True
How can we determine the order and location of genes within a chromosome?
By using recombination frequencies
Describe recombination
Two chromatids cross over and swap genetic material at random points.
What is the proportion of recombinant gametes termed by?
Recombinant frequency.
How is the recombinant frequency determined?
(amount of recombined genes)/(total amount of genes)
What is the recombinant frequency of unlinked (distant) genes?
Around 50%
What is the recombinant frequency of close genes?
0-50%
Why is there a higher chance that genes close together are linked?
Because it is less likely that the chiasmata will be formed between them
What is the difference between a gene pool and a population?
A population is a group of individuals of the same species and the gene pool is the sum of all of the genes in the population
How can we predict genotypes on a population?
Using the Hardy-Weinberg equation
p2+2pq+q2=1
Review this (last lecture)
What are the 7 ways that allele frequencies can change?
Non-random mating
Random genetic drift
Bottleneck effect
Founder effect
Natural selection
Gene flow or migration
Mutation
Describe random genetic drift
Random change in allele frequencies due to sampling error
Describe the bottleneck effect
Population reduction which causes a random shift in allele frequency
Describe the founder effect
When a random group of a population becomes geographically isolated and the allele frequency randomly shifts
What are the 3 types of directional selection?
Stabilising selection
Directional selection
Disruptive selection
Describe sexual selection
When members of a population are more likely to mate due to some sexually attractive trait that they possess
What is frequency dependent selection?
When selectional is directional but changes direction based on the amount of individuals in that species.
What is a Cline?
A gradual or geographic change in genetic composition
What is migration?
When an individual from another population successfully mates to a gene pool
