Module 6: Mutations + Hox Genes Flashcards
What is an Operon?
A cluster of genes under the control of a promoter.
Give one example of apoptosis in the development of an embryo:
- Formation of Synapses
- Separation of digits (e.g toes or fingers)
Name all the kingdoms that use homeobox genes:
Fungi, Animalia and Plant.
Explain how the failure of a control mechanism can prevent the separation of fingers.
Transcription factors not produced, and-so transcription of the hox gene may not occur -> Molecules signaling apoptosis aren’t produced-> apoptosis does not occur.
Gene:
A specific segment of DNA whose nucleotide sequence codes for a specific protein.
Locus:
The location of a gene on a chromosome.
Alleles:
alternative forms of the same gene which occupy the same locus on a pair of homologous chromosomes.
Genotype:
The genetic constitution of an organism comprising all the genes possessed by an individual.
Phenotype:
The observable characteristic that is the consequence of a genotype.
Mutations:
Random and spontaneous changes to the base sequence
Somatic mutation:
Mutation on non-reproductive cell -Only affects the individual organism
Germ-line mutation:
Mutation on gametes that are inheritable.
Causes of Mutations:
Spontaneous, chemicals, radiation, viruses `
Example of beneficial mutation:
Sickle cell anaemia is a germline mutation that causes anaemia but makes the victim resistant to malaria.
Degenerate DNA:
Multiple codons code for the same amino acid.
Substitution Mutation:
A base pair is spontaneously replaced with another - this affects only one base triplet codon - effects at protein level.
Deletion Mutation:
A base pair/gene is discarded -> alters the reading frame of the gene -> irreversible
Addition Mutation:
A base pair is inserted into the DNA or duplicated - > caused by transposable elements or errors - > may alter splicing -> causes a frameshift
Homozygous:
individuals who carry two identical alleles.
What are the 3 types of substitution mutation:
Nonsense Mutation, Missense Mutation, Silent Mutation
Nonsense Mutation;
Premature stop codon results in a shorter unfinished protein.
Silent Mutation:
Change in DNA sequence does not affect sequence of amino-acids forming protein, due to degenerate DNA.
Missense Mutation:
A genetic alteration where a single base pair substitution alters genetic code to produce a different amino acid.
Why are chromosomal mutations severe:
Large regions of DNA are lost and damaged.
What are introns?
Non-coding regions.
What are exons?
Coding Regions.
Purines:
Adenine and Guanine
Pyramidines:
Cytosine and thymine
Chromosome Mutation:
Deletion, Duplication, Translocation, Inversion
Post Translational control:
The polypeptide is modified after it has been synthesised.
What are the methods of post translational control?
Addition of non-protein groups.
Modifying amino acids and the formation of bonds.
Folding or shortening of proteins.
Modification by cAMP.
What are the methods of post translational control?
Addition of non-protein groups.
Modifying amino acids and the formation of bonds.
Folding or shortening of proteins.
Modification by cAMP.
Modification by cAMP:
cAMP binds to a receptor protein which then undergoes a conformational change into a transcription factor which increases the rate of transcription.
What are the 3 types of Eukaryotic Transcriptional control?
Chromatin Structural changes, Histone modification, and Transcription Factors.
Transcription Factors:
Activators - Allow/ facilitate transcription
Repressors - Inhibit transcription, prevent binding of RNA polymerase
Chromatin Structural Changes:
Heterochromatin -> tightly wound DNA in chromosomes
Euchromatin -> loosely wound DNA that is present in interphase
Histone modification:
Acetylation reduces the +ve charge of histones, causes DNA to coil less tightly allowing transcription.
Methylation increases +ve charge of the Histone, causing DNA to coil more tightly preventing transcription.
The 3 types of Mutagens?
Physical, chemical, and biological agents.
Chromosomal Mutations:
Deletions
Duplication
Translocation
Inversion
Chromosomal Mutations: Deletion
A selection of chromosome breaks off and is lost within the cell.
Chromosomal Mutations: Duplication
Sections get duplicated on a chromosome
Chromosomal Mutations: Translocation
A section of one chromosome breaks off and joins another non-homologous chromosome.
Chromosomal Mutations: Inversion
A section of chromosome breaks off, is reversed, and then joins back onto the chromosome.
Outline Lac Operon:
In the presence of glucose a repressor protein in bound to an operator. Once glucose is removed and replaced with lactose, lactose binds to the repressor protein, pulling it away. This allows for the RNA polymerase to bind to a promoter and catalyse the formation of phosphodiester bonds between RNA nucleotides.
What is Lac Operon?
Lac operon refers to a group of three genes lacZ, lacY, and LacA, involved in the metabolism of lactose. They are structural genes coding for three enzymes and they are transcribed onto a long molecule of mRNA. LacI is a regulatory gene responsible for the formation of the Repressor protein.
Role of Cyclic AMP in lac operon:
The rate of transcription needs to be high to produce the required quantity of enzymes to breakdown lactose. In the absence of Glucose, high quantities of cAMP are synthesised. In the presence of Glucose, cAMP production is reduce/inhibited and-so the rate of transcription decreases.
Post Transcription/ Pre-translational Control:
RNA Processing and RNA editing
RNA processing:
A cap (modified nucleotide) is added to the 5' end and a tail (long chain of adenine nucleotides) is added to the 3' end. Splicing also occurs, where the RNA is cut at specific points, where the introns are removed and the exons are joined together.
RNA editing:
The nucleotide sequence of some mRNA molecules can be changed through base addition, deletion, or substitution. This results in the synthesis of different proteins with differing functions, increasing the range of proteins produced by a single mRNA molecule of gene.
What is the product of transcription?
pre-mRNA
What type of mRNA binds to ribosomes during synthesis?
Mature-mRNA
Translational Control Mechanisms:
Degradation of mRNA, Binding of inhibitory proteins, Activation of initiation factors.
Degradation of mRNA (translational Control):
More resistant mRNA molecules last longer in the cytoplasm and therefore undergo more protein synthesis.
Binding of inhibitory proteins (translational control)
The binding of inhibitory proteins prevent the mRNA from binding to ribosomes, preventing protein synthesis.
Activation of initiation factors (Translational control):
Initiation factors aid the binding of mRNA to ribosomes.
Protein Kinases:
Enzymes that catalyse the addition of phosphate groups to proteins. The addition of the phosphate group alters the protein’s tertiary structure and therefore its function. They regulate cell activity.
Post Translational Control:
Modifications to synthesised proteins:
- Folding/ shortening
- Addition of non-protein groups.
- Modifying amino acid sequence.
- Modifications by cAMP (Increases rate of transcription of structural genes).
Types of Symmetry (Body plans):
Radial, bilateral and Asymmetry.
Radial Symmetry:
Seen in diploblastic animals. e.g jelly fish (top and bottom)
Bilateral symmerty:
Seen in most animals, meaning they have a left and right side with a head and tail.
Asymmetry:
Seen in sponges
What is the role of Apoptosis in shaping organisms?
Apoptosis is used to discard unwanted cells and tissues to shape body parts. e.g removing webs between fingers.
What is the role of mitosis in shaping organisms?
Cell proliferation and tissue growth.
Factors affecting expression of regulatory genes:
External factors causing stress (disturbance to homeostatic balance e.g change in temp).
Internal factors due to release of hormones or physiological stress.
Drugs
Method for carrying out artificial selection for genetic control.
At the start the organisms with your desired trait may be heterozygous, if the allele is dominant. Therefore you should breed the organisms together and only breed them if they only produce offspring with the desired trait. Continue this for many generations and then carry out a test cross.
