Genetics of living systems Flashcards
Define mutation.
Change in the base sequence of DNA.
Define point mutation.
One nucleotide is affected.
What are the affects of substitution?
New codon which codes for a different amino acid which leads to a different primary structure.
What feature of the genetic code means that the primary structure may not be affected by the substitution of bases?
Degenerate
Why may a new primary structure not have a huge impact on the function of the protein?
Does not make up the active site.
What mutations lead to a frameshift?
Insertion or deletion
When will the reading frame not be altered by insertion or deletion?
If the number of nucleotides change by a multiple of three.
If multiples of three are added or deleted from the sequence of bases, will the protein formed be affected?
Yes, as new amino acids are added (or taken away)
What are the possible effects of mutations?
No effect, damaging, beneficial
When can a mutation be damaging?
Proteins are no longer synthesised.
When can a mutation be beneficial?
New useful characteristic in the phenotype.
What increase the rate of mutations?
Mutagens
How do mutations occur?
Spontaneously
What is a mutagen?
Chemical, physical, or biological agent which causes mutations.
Define depurination.
Loss of a purine base.
Define depyrimidination.
Loss of a pyrimidine base.
What are free radicals?
Oxidising agents
How can free radicals cause mutations?
Disrupt base pairing during DNA replication.
Why are antioxidants called anticarcinogens?
Their ability to negate effects of free radicals.
Give an example of a physical mutagens.
Ionizing radiation e.g. X rays
Give an example of a chemical mutagen.
Deaminating agents.
Give 3 examples of biological agents which act as mutagens.
Viruses, base analogs, alkylating agents.
How does ionizing radiation act as a mutagen?
Break one or both strands of DNA
How does deaminating agents act as a mutagen?
Alter bases in DNA such as converting C to U in DNA, changing the base sequence.
How do viruses act as mutagens?
Viral DNA may insert itself into a genome, changing the base sequence.
How do base analogs act as mutagens?
Incorporated into DNA in place of the usual base during replication, changing the base sequence.
How do alkylating agents act as mutagens?
Methyl or ethyl groups are attached to bases resulting in the incorrect pairing of bases during replication.
Where might a mutation occur for it to be silent?
Introns
What are nonsense mutations?
Result in a codon becoming a stop codon. So shortened protein is synthesised.
What are missense mutations?
Result in the incorporation of an incorrect amino acid.
Where do gene mutations occur?
Single genes or sections of DNA.
What do chromosome mutations affect?
Whole chromosome
What are the changes in chromosome structure as a result of a chromosome mutation?
Deletion- Section of chromosome breaks off
Duplication- Section gets duplicated
Translocation- Section of one chromosome breaks off and joins another non-homologous chromosome
Inversion- Section breaks off, is reversed, joins back onto the chromosome
What is morphogenesis?
Regulation of the pattern of anatomical development.
Why are fruit flies a popular choice for studies?
Small, easy to keep with a short life cycle.
Define homeobox genes.
Group of genes which contain a homeobox.
What is the homeobox?
Section of DNA 180 base pairs long coding for a part of the protein 60 amino acids long that is highly conserved in plants, animals and fungi.
What does highly conserved mean?
Similar in…
What is the homeodomain?
Part of the protein which binds to DNA and switches other genes on or off, so are regulatory genes.
What is hox genes used interchangeably with?
Homeobox genes
What are hox genes?
Group of homeobox genes that are only present in animals.
What are hox genes responsible for?
Correct positioning of body parts.
In animals, where are Hox genes found?
Gene clusters
What name is given to animals which have 2 primary tissue layers?
Diploblastic
What name is given to animals which have 3 primary tissue layers?
Triploblastic
What do Hox genes in the head control?
Development of mouthparts
What do Hox genes in the thorax control the development of?
Limbs, wings or ribs
What are individual vertebrae and associated structures developed from?
Somites
What are somites?
Segments in the embryo
What directs somites?
Hox genes
Name 3 types of symmetry found in animals.
1) Radical symmetry
2) Bilateral symmetry
3) Asymmetry
What is radical symmetry?
Seen in diploblastic animals. No left or right sides, only a top and bottom.
Give an example of a diploblastic animal.
Jellyfish
What is bilateral symmetry?
Have a left, right, head and tail
What is asymmetry?
Seen in sponges with no lines of symmetry
What two processes are essential in shaping of organisms?
Mitosis
Apoptosis
What is apoptosis?
Programmed cell death
How does mitosis give shape?
Leads to growth
How does apoptosis give shape?
Removes unwanted cells and tissues
What regulates both mitosis and apoptosis?
Hox genes
What affects the expression of regulatory genes?
Internal and external environment.
Give a factor which is both internal and external.
Stress
How can the way in which genes are regulated by categorised?
Transcriptional- Genes turned on or off
Post-transcriptional- mRNA can be modified which regulates translation and the types of proteins produced
Translational- Translation can stopped or started
Post-translational- Proteins can be modified after synthesis which changes their functions.
Give the mechanisms which can affect the transcription of genes.
- Chromatin remodelling
- Histone modification
- Lac operon
What is heterochromatin?
Tightly wound DNA causing chromosomes to be visible during cell division.
What is euchromatin?
Loosely wound DNA during interphase.
Why is transcription not possible when DNA is tightly wound?
RNA polymerase cannot access the genes.
Which can be freely transcribed, hetero or euchromatin?
Euchromatin
Why is it important that only euchromatin can be transcribed?
Ensures protein synthesis doesn’t occur in cell division. So proteins needed for cell division are synthesised in time.
Why does DNA coil around histones?
Histones are positively charged and DNA is negatively charged.
What is the affect of acetylation or phosphorylation?
Reduces positive charge on histones which causes DNA to coil less tightly, so certain genes can be transcribed.
What is the affect of methylation?
Makes histones more hydrophobic so they bind more closely together, so DNA coils more tightly, preventing transcription.
What is epigenetics?
Describes control of gene expression by modification of DNA.
What is an operon?
Group of genes that are under the control of the same regulatory mechanism and are exposed at the same time.
Where are more operons found?
Prokaryotes
What is the lac operon?
Group of three genes,.
What are the three genes used in the metabolism of lactose?
lacZ, lacY, lacA
What is the regulatory protein in lactose?
lacI
Where is lacI found?
Near top of operon and codes for a repressor protein that prevents the transcription of the structural genes in the absence of lactose.
What codes for a repressor protein?
A regulatory gene
How does a repressor protein prevent transcription?
A regulatory gene codes for a regulatory protein which binds to the operator and prevents the binding of RNA polymerase, preventing transcription.
What is it called when RNA polymerase cannot bind to the promotor?
Down regulation
What is the promotor?
Section of DNA that is the binding site for RNA polymerase
What increases the rate of binding of RNA polymerase?
The binding of another protein, cAMP receptor protein (CRP). Only possible when cAMP is bound to CRP.
What can affect the post-transcriptional/ pre-translational control?
RNA processing
RNA editing
What is RNA processing?
Pre-mRNA is spliced into mature mRNA which then has a cap added to the 5’ end and a tail to the 3’ end. These help to stabilise mRNA and delay degradation in the cytoplasm. Cap aids the binding of mRNA to ribosomes.
What is RNA editing?
Nucleotide sequence of mRNA molecules can be changed through base addition, deletion or substitution. This increase the range of proteins which may have different functions.
What are the mechanisms which regulate the process of protein synthesis?
1) Degradation of mRNA- the longer it will last, the more of the protein can be synthesised.
2) Binding of inhibitory proteins to mRNA prevents binding to ribosomes and hence the synthesis of proteins.
3) Activation of initiation factors which aid the binding of mRNA ribosomes.
4) Protein kinases catalyse the addition of phosphate groups to proteins, this changes the tertiary structure and so the function of the protein.
How are protein kinases activated?
By the secondary messenger cAMP
What is post-translational control?
- Addition of non-protein groups
- Folding or shortening of proteins
- Modifying formation of bonds
