19 - Genetics of living systems Flashcards
What is a mutation?
Change in the base sequence of DNA
What are the 3 types of mutation?
- Substitution 2. Deletion 3. Insertion
What is a substitution mutation?
Replacement of one or more DNA bases with others
What is a deletion mutation?
When one or more nucleotides are removed (i.e., deleted) from the DNA sequence
What is an insertion mutation?
Where one or more bases are added to the DNA sequence
What is it called when a mutation only affects one nucleotide?
Point mutation
When might a mutation affect a protein’s primary structure?
When it creates a new codon which codes for a different amino acid
What are the 3 different types of mutation effects?
- No effect 2. Damaging 3. Beneficial
When would a frameshift mutation occur?
When a deletion or addition mutation occurred in a number of bases that is not a multiple of 3
What would a frameshift mutation cause?
Every successive codon from the point of the mutation onwards would be different, so the protein produced would be completely different
Would a protein still be affected by a deletion or insertion mutation which wasn’t a frameshift mutation?
Yes, as there would still be a new amino acid added, but the effects would likely be less
What are 3 possible reasons why a mutation may have a neutral effect on a protein’s structure?
- Mutation changes a base, but the amino acid which the triplet codes for is the same 2. Mutation causes a different amino acid to be produced which is chemically similar to the original 3. The triplet affected may code for an amino acid which isn’t essential to the protein’s function, such as one located away from the active site
Would a mutation with a neutral effect affect the whole organism?
No it wouldn’t affect the whole organism
How can a mutation make a protein more or less active?
By changing the shape of its active site
Does a mutation which changes a protein’s active site mean the organism is less likely to survive?
Not necessarily- the mutation may even be beneficial
Give an example of a mutation with a beneficial effect for an organism?
A mutation which enabled a bacterial enzyme to break down an antibiotic more effectively
Give an example of a mutation with a negative effect for an organism?
Deletion mutation causing changes in the CFTR protein which lead to cystic fibrosis
How can a mutation prevent a protein from being produced?
If the mutation is at the start of the gene and RNA Polymerase can’t bind to it, so the protein won’t be produced
What are 2 reasons a mutation may be harmful to an organism?
- Protein may not be produced at all 2. Protein may be produced, but in a non-functional form
What increases the rate of mutation?
Mutagens
What is a mutagen?
A chemical, biological or physical agent which causes mutations
What is depurination?
The loss of a purine base from DNA
What is depyrimidination?
Loss of a pyrimidine base from DNA
How does depurination or depyrimidination usually happen?
Spontaneously
What type of mutation could depurination or depyrimidination lead to?
Insertion if a new base filled the gap left
What are 2 chemical mutagens?
- Free radicals 2. Deaminating agents
What could a deaminating agent do to cytosine?
Change it to uracil
Why are antioxidants also known as carcinogens?
Due to their ability to negate the effects of mutagenic free radicals
What is an example of a physical mutagen?
Ionising radiation such as x-rays
How would x-rays act mutagenically?
Break one or both DNA strands, with the repair of the strand often causing mutations
What are 3 examples of biological mutagens?
- Alkylating agents 2. Base analogues 3. Viruses
How does a virus act as a mutagen?
By inserting viral DNA into the genome
How do alkylating agents act as mutagens?
Attach methyl or ethyl groups to bases, causing incorrect pairing during replication
How do base analogues act as mutagens?
They are incorporated into DNA in lieu of a normal base
What is a chromosome mutation?
One which affects the whole chromosome or a number of chromosomes within the cell
When do most chromosome mutations occur?
During meiosis
What is a deletion chromosome mutation?
A section of a chromosome breaks off and is lost within a cell
What is a duplication chromosome mutation?
Sections of a chromosome duplicated
What is a translocation chromosome mutation?
A section of one chromosome breaks off and attaches to a non-homologous chromosome
What is an inversion chromosome mutation?
A section of chromosome breaks off, is reversed, and then rejoins onto the chromosome
What is a housekeeping gene?
One which codes for enzymes necessary for metabolic processes such as respiration
What are tissue-specific genes?
Ones which code for protein-specific hormones
What is a transcription factor?
Proteins which bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription
What are the two types of transcription factor?
- Activators 2. Repressors
What do activators do?
Factors which increase the rate of transcription
What do repressors do?
Factors which decrease the rate of transcription
How do transcription factors work?
Bind to specific DNA sites near the start of their target genes (in eukaryotes) and promote/repress the action of RNA Polymerase
What do transcription factors bind to in prokaryotes?
Operons
What 3 things can be contained in an operon?
- Clusters of structural genes 2. Control elements 3. A regulatory gene (sometimes)
What do structural genes do?
Code for useful proteins i.e. enzymes
What 2 things do control elements contain?
- Promoter 2. Operator
What is a promoter?
DNA located before the structural genes, which RNA polymerase binds to
What is an operator?
A DNA sequence which transcription factors bind to
What 2 things can regulatory genes code for?
Activators or repressor
What allows bacteria to respond to environmental changes?
Gene regulation
What 4 things is gene regulation necessary for in eukaryotes?
- Responding to changes in external environment 2. Responding to changes in internal environment 3. Cell specialisation 4. Cell coordination
What are the 4 stages at which genes can be regulated?
- Transcriptional 2. Post-transcriptional 3. Translational 4. Post-translational
How can genes be regulated at a transcriptional level?
Genes can be turned on or off
How can genes be regulated at a post-transcriptional level?
mRNA can be modified, which regulates translation and the types of proteins produced
How can genes be regulated at a translational level?
Can stop or start translation
How can genes be regulated at a post-translational level?
Proteins can be regulated after translation, which changes their function
What are 4 methods of transcriptional gene regulation?
- Cyclic AMP 2. Histone modification 3. Chromatin remodelling 4. Lac operon
What is a chromatin?
DNA molecules that are tightly coiled around proteins call histones.
What is heterochromatin?
Tightly packed chromatin
When does heterochromatin allow chromosomes to be seen?
During cell division
When does euchromatin allow chromosomes to be seen?
During interphase
What is euchromatin?
Loosely packed chromatin
In which of heterochromatin and euchromatin can genes be transcribed and why?
Euchromatin, as heterochromatin is too tightly packed
Does protein synthesis occur during cell division, and why/why not?
No as you can’t transcribe genes from heterochromatin
Why is it important that genes cannot be transcribed from heterochromatin?
Prevents complex and energy-consuming process of protein synthesis occurring when cells are dividing
What type of gene regulation is the fact that genes can’t be transcribed from heterochromatin?
Transcriptional
Why does DNA condense around histones?
Because they are positively charged and DNA is negatively charged
What are 2 methods of making histone groups less positive?
Acetylation and phosphorylation
How is the acetylation or phosphorylation of a histone an example of transcriptional gene regulation?
Makes DNA bind to histones more loosely, allowing certain genes to be transcribed
How does methylation of histones affect them?
Makes them more hydrophobic
How is methylation of histones an example of transcriptional gene regulation?
Because it makes them more hydrophobic they bind together more tightly, so the DNA coils around them more tightly and less gene transcription can take place
What is epigenetics?
The control of gene expression by the modification of DNA
What is an operon?
A unit made up of linked genes that is thought to regulate other genes responsible for protein synthesis. Its genes are expressed at the same time
Are operons present in eukaryotes?
Yes
Why are operons more common in prokaryotes?
Prokaryotic genomes are smaller and simpler
What is an advantage of using operons?
They are a very efficient way of saving resources as if certain gene products aren’t needed you can switch off all the genes involved in their production
What 3 genes make up the lac operon?
lacZ, lacY, lacA
What is the lac operon involved in?
The metabolism of lactose
What types of genes are lacA, lacY and lacZ and why?
Structural genes as they code for enzymes and are transcribed onto one long piece of mRNA
What is the preferred respiratory substrate of E.coli?
Glucose
When would E.Coli use lactose as a respiratory substrate?
When glucose is in short supply
What is located near the lac operon and what does it code for?
The regulatory gene lac L, which codes for a repressor protein that prevents the transcription of the structural genes in the absence of lactose
What is down regulation?
Binding of repressor protein to an operator, whcih prevents binding of RNA polymerase
What happens to the lac operon when lactose is present?
Lactose binds to the repressor protein and causes it to change shape so that it can no longer bind to the operator, so gene transcription can occur
When is CRP binding possible?
When CRP is bound to cyclic AMP
How can the rate of transcription of RNA polymerase be increased?
By binding CRP
How does glucose regulate the lac operon?
- When glucose levels are high, cAMP levels are low. 2. cAMP receptor protein (CRP), aka CAP, binds cAMP 3. cAMP-CRP acts as an activator of the operon
What is a cap?
Modified nucleotide
What is a tail?
Long chain of adenine nucleotides
Which ends do the cap and tail bind to?
Cap to 5’ end, tail to 3’ end
What 2 things do the cap and tail both do?
- Stabilise mRNA 2. Delay degradation in the cytoplasm
What does the cap do which the tail doesn’t?
Aids binding of mRNA to ribosomes
Where does splicing and the addition of cap and tail occur?
In the nucleus
Why would point mutations be done deliberately by the cell?
So that a greater range of proteins can be produced from the same mRNA molecule or gene
What are 2 methods of post-transcriptional gene regulation?
- RNA processing 2. RNA editing
What are 4 methods of translational gene regulation?
- Degradation of mRNA, with quicker degradation in cytoplasm meaning less protein synthesis 2. Protein kinases 3. Activation of initiation factors which aid binding of mRNA to ribosomes 4. Binding of inhibitory proteins to mRNA which prevent it from binding to ribosomes
What are protein kinases?
Enzymes that activate or inactivate other proteins by phosphorylating them
What often activates protein kinases?
cAMP
How does phosphorylating a protein activate it?
Changes its tertiary structure
What are 5 methods of post-translational gene regulation?
- Addition of non-protein groups 2. Modifying amino acids 3. Formation of bonds such as disulfide bridges 4. Folding and shortening of proteins 5. Modification by cAMP
What is morphogenesis?
The regulation of the pattern of anatomical development
What is a body plan?
The general structure of an organism
What are body plans controlled by?
Proteins produced by Hox genes
What are homeobox genes?
Sequences of genes that control the development of specific structures
What is a homeobox?
A 180-nucleotide sequence within homeotic genes and some other developmental genes that is widely conserved in animals, plants and fungi
What does the homeodomain do?
Binds to DNA and switches other genes on or off
What do homeobox sequences code for?
Part of a protein called the homeodomain
What 2 processes are involved in the development of body plans?
Mitosis and apoptosis
What are Hox genes found in in animals?
Clusters
What are Hox genes?
A group of homeobox genes only present in animals
What does the order in which Hox genes appear along the chromosome determine?
The order in which their effects are expressed in the organism
What is the difference between diploblastic and triploblastic animals?
Diploblastic have 2 primary tissue layers, triploblastic have 3
What is a common feature of animals?
They are segmented
What are somites?
Segmented blocks of tissue in the embryo that later differentiate into vertebrae, ribs, and skeletal muscles due to the effects of Hox genes
What 2 types of symmetry are found in the body shape of animals?
- Radial 2. Bilateral
Do all types of animal show symmetry?
No, for example sponges show asymmetry. But most do.
What are 2 ways apoptosis can regulate the development of the body?
- Remove unwanted cells and tissues 2. Release chemical signals which stimulate mitosis and cell proliferation
What can influence the expression of regulatory genes?
The internal and external environmental
What is an example of a drug which interferes with Hox genes?
Thalidomide
