6.1 Genetics And Evolution Flashcards
What are the steps of transcription?
- DNA unwinds due to action of DNA helicase
2.Template strand of DNA is used and mRNA forms as mirror image so bases still match (U replaces T)
3.mRNA leaves nucleus
What are the steps of translation?
- mRNA attaches to ribosome
- Each tRNA has complimentary anticodon to codon of the mRNA (anticodon= matching the codon of the DNA copied
- The first tRNA carries the first anticodon which forms hydrogen bonds with the start codon of the mRNA
- Second tRNA brings second amino acid and a peptide bonds form between amino acids
- Ribosome moves along the mRNA
- The first tRNA (now without amino acid) is released and this continues along the chain until a stop codon is reached
What is the definition of a mutation?
A change in the sequence of an amino acid
When do mutations occur?
Randomly during cell division (usually during DNA replication)
What is the definition of a mutagen?
Chemical,physical or biological agents that cause mutations
What is a nonsense mutation?
A stop codon is produced causing a shortened protein to be synthesised
What is a missense mutation?
An incorrect amino acid being incorporated
What are the three types of mutation?
Silent- (no effect) proteins still functional
Damaging- Protein isnt synthesised or non functional
Beneficial- Protein synthesised may give useful characteristics
What are the three types of point mutation?
Substitution,addition or deletion of a nucleotide base
What is a chromosome mutation?
Mutations that affect large regions of DNA within chromosomes
What feature of a DNA molecule is changed as a result of mutation?
The sequence of nucleotides
What are the possible effects of a mutation on the structure and function of a protein?
- Sequence of amino acids can alter tertiary and quarternery structure
- Can cause it to fold into a different shape which means if it has an active site it may be non functional
- Or it may have no effect or a beneficial effect
What is apoptosis?
Programmed cell death (controlled)
What is necrosis?
Damaged cell death (occurs after trauma)
What is the sequence of apoptosis?
- Enzymes break down cell cytoskeleton
- Cytoplasm becomes dense with organelles tightly packed
- Cell surface membrane changes and small bits called blobs form
- Chromatin condense and nuclear envelope breaks (DNA fragments)
- Cell breaks into vesicles and engulfed by phagocytes
How is apoptosis controlled?
Range of cell signals
- Cytokines
- Hormones
- Growth factors
- Nitric oxide
How does nitric oxide bring about apoptosis?
Makes membrane more permeable to H+ ions
What happens if apoptosis is not balanced?
Too much= cell loss and degeneration
Not enough= leads to formation of tumours
Where is the lac operon found?
In e-coli
What is an operon?
A length of DNA coding for proteins and control sites
How do proteins in the lac operon get induced?
In the presence of lactose =
What are the requirements for lactose digestion and why are these not made all the time?
- Transport protein for for the uptake of lactose across the cell membrane
- Requires an enzyme to break lactose into galactose and glucose
- In absence of lactose this would be a waste
What are structural genes and what are they in the lac operon?
- Encode proteins involved in uptake and utilisation of lactose
- Known as Z (beta galactosidase) and Y (Lactose permease)
What is the purpose of the operator in the lac operon?
Can turn structural genes on and off
What is the purpose of the promoter?
Length of DNA where RNA polymerase binds
What is the purpose of a regulatory gene?
To encode a repressor protein
Not part of the operon
What’s is the sequence of events in a non induced operon?
1.Regulatory gene is expressed and repressor protein is synthesised
2. RP binds to operator and blocks part of promoter so RNA polymerase cannot bind
3. Genes are not transcribed and Beta galactosidase and lactose permease are not expressed
Why is no transcription of structure genes in the absence of lactose good?
Saves energy for cell and cell resources such as amino acids
What is the sequence of events with an induced operon?
1.The regulatory gene is expressed and represssor protein is synthesised
2. Lactose binds to repressor so protein changes shape and cannot bind
3. RNA polymerase can bind to promoter
4. MRNA is then transcipted and transcribed for proteins Z and Y
5. Beta galactosidase and lactose permease are expressed
What happens if both glucose and lactose are present around e-coli but glucose conc is low.
- Levels of CAMP are high and readily binds with CAP
- CAP- CAMP complex binding leads to enhanced RNA polymerase binding
- High rate if transcription and translation of lac operon structural genes
- Leads to production of glucose from lactose
What happens in the lac operon when the conc of both glucose and lactose is high?
- CAMP is decreased in presence of glucose
- SNA does not bind to DNA as efficiently as
- Low rate of transcription
- Production of glucose is diminished
What is the definition of gene expression?
- The gene transcribed and translated into a protein
What three process control whether or not something gets transcribed?
Operons- group of genes under the control of a regulatory mechanism
Chromatin remodelling- Protein synthesis does not happen while DNA is tightly wound as RNA polymerase cannot access it
Histone remodelling- histones have a positive charge, DNA has a negative: Adding Acetyl or phosphate groups reduce positive charge so DNA uncoils, Adding methyl groups makes them more hydrophobic so coil tighter
What two processes control post transcriptional control?
RNA processing- The product of transcription needs to be modified before it can bind to a mature RNA
RNA editing- mRNA can be a changed similarly to point mutations
What are the three modifications of RNA processing?
- A modified nucleotide cap added to help ribosome attachment
- A tail of adenine molecules to stabilise and reduce degradation
- Introns (non coding DNA) removed and exons (coding DNA)
What is translational control for?
To regulate protein synthesis
What are the role of protein kinases?
To regulate cell activities such as protein synthesis
Enzymes which catalyse addition of phosphate groups to proteins which changes tertiary structure
How are mRNA adjusted in post-translational control?
- Addition of non-protein groups
- Modifying amino acids and adding disulphide bridges
- FOlding or shortening proteins
- Modification of cAMP
What are homeobox genes?
Master genes which control the body plan
What is the difference between asymmetrical,bilateral and diploplastic body plans?
- Bilateral- Has anterior and posterior
- Asymmetry- No lines of symmetry
- Diploplastic- Has radial symmetry no left or right
What is the definition of a homeobox?
- A region of DNA that codes for a domain which can bind to DNA and found in all animals
What is the definition of hox genes?
- A distinct family of homeobox genes which play a role in determining where body parts grow from in flies
How do homeobox genes work?
- Proteins produced act as transcription factors
- Molecular switches for mRNA by binding to specific DNA sequences
What is the homeobox sequence?
- The same 180 base sequence encoding the same sequence of amino acids
- Binds to groove in DNA double helix
Why are fruit flies studied?
- Small so easy to study in lab
- Quick lifecycle
- Less ethical issues
- Visual body segments in life cycle
Why are homeobox genes needed?
Because the body plan requires a coordinated expression of a set of genes at the proper times
In what order are homeobox genes activated in?
The order they are expressed along the body of an organism
What does the sequence of homeobox genes prove?
- That the home optic protein causes expression when a specific promoter sequence shared by a number of genes
Why are homeobox genes similar in many animals?
- Evolved from same common ancestor
- Highly conserved
- Mutations in the homeobox gene are likely to be fatal
EXAMPLE: Suggest how homeobox genes would affect brain development?
- Homeotic genes affect development of body plan
- These control the development of different parts of the brain
- Gives an anterior and posterior section
- Does this by controlling the region the protein binds to in RNA synthesis
- Regulates levels of mitosis apoptosis
What is an autosome?
- Chromosomes which are not a sex chromosome
What is an unlinked gene?
Genes on separate chromosomes
What is co-dominance?
When both alleles are equally dominant so both genes are equally expressed
E.g red and white flowers produce pink offspring
What is the classical phenotypic ration for a codominant gene of two heterozygous parents?
1:2 ratio
What are sex linked traits?
- Genes found on X chromosome but not on Y
Why are sex linked genes prevalent in causing illness?
- X chromosomes have more genes?
- For each gene exclusively on X females have two x while males only have one x
- Males will always display recessive allele
What are some examples of variation due to environmental influence?
CHlorois- Cells do not produce regular amounts of chlorophyll in order to conserve resources and reduce photosynthesis
Animal body mass
How is genetic variation created?
Meiosis and random fusion of gametes
Variety of different alleles
What is the difference between continuous and discontinuous variation?
- Continuous- two extremes and then every value in between
- Discontinuous- set groups of data
What occurs when genes are linked?
More likely for genes to be inherited together as less likely to be seperated
What would be expected if the expected ratio was 1:1:1:1 and the actual genotype ratio was 1:5:5:1
Genetic linkage
What is the equation for recombination frequency?
Number of recombinant offspring/total number of offspring x 100
What is recombination frequency?
- The measure of the amount of crossing over that has happened in meiosis
What does a recombinant frequency of 50% or below mean?
Linkage. The closer the genes the lower the frequency
When is a chromosome map used?
To map the recombinant frequency’s of genes to see how closely the genes are linked
What s the definition of recombination?
Exchange of alleles between homologous chromosomes due to crossing over
When is the chi squared test used?
- To find if there is a significant difference between observed and expected results
When can chi squared be used?
- Data is in categories
- There is a theory for wh there should be expected values
- Large sample size
- Data is in counts
- No scores of 0
What is meant by a null hypothesis?
That there is no statistically significant difference between the observed and the expected data. Any difference s due to
How is the number of degrees of freedom calculated?
Number of categories - 1
What happens if chi squared is smaller than the critical value?
Hen differences are due to chance so the genetic theory of dihybrid crosses explains this result
What is epistasis?
- When genes on different chromosomes or at different loci can interact to affect one phenotypic characteristic
What is recessive epistasis?
- When homozygous recessive alleles at the first locus prevent expression of the allele at the second locus
What is dominant epistasis?
- The dominant allele of one gene loci prevents the second gene being expressed (whatever allele)
What dihybrid ratios suggest epistasis?
- ANy ration which is not 9:3:3:1
Why might epistasis happen?
- The first genes working to code for enzymes to produce pigment may inhibit the second
