Cellular Control Flashcards
What is a mutation?
A random change in the genetic material
Give examples of things that are mutagenic
Tobacco smoke
Ionising radiation e.g UV-light, X-rays, Gamma rays
In what type of cell division would an inheritable mutation occur in?
Meiosis
Affects gametes which then determines genetic makeup of the child
What are the two main types of mutation?
Point mutation - 1 gene is substituted for another
Insertion or deletion mutation - 1 or more nucleotides are inserted or deleted from a length of DNA
What are the 3 types of point mutation?
Silent
Missense
Nonsense
What is a silent mutation?
Nearly all amino acids have more than one triplet that codes for them
A silent mutation occurs when there is point mutation but the new triplet sequence still codes for the same amino acid
As such the protein is the same and the mutation is unnoticeable
What is a missense mutation?
When the change in triplet sequence causes a change in the amino acid sequence and thus a change in the primary, secondary and tertiary structures of the protein
This changes the 3D shape of the protein and can make it less effective at carrying out its function
Give an example of a condition that is caused by a missense mutation
Sickle cell anemia
Caused by a change in the gene for the B-Polypeptide haemoglobin
What is a nonsense mutation?
Where the change in the triple sequence causes it to become a stop codon
This then means the protein structure is incomplete and it will not carry out its function
Give an example of a condition caused by a nonsense mutation
Muscular Dystrophy
What is a frameshift?
Caused in insertion or deletion mutations
When a nucleotide is inserted or deleted in the sequence it causes all the other bases to move along
Because bases are read in groups of 3 this then changes all of the triplets that are down the chain from the mutation
What affect does a frame shift have on the polypeptide chain?
Because a frameshift affect all of the triplets after the mutation the amino acid sequence is greatly disrupted
This has a huge impact on the primary and subsequent tertiary structures and so the protein is unable to carry out its function
What is an expanding nucleotide triple repeat?
Some genes contain a repeating triplet such as -CAG CAG CAG-
The number of CAG triplets will increase due to meiosis from generation to generation
Once this goes past a critical number one might develop a genetic disorder
What is the lac Operon?
The gene sequence which codes for genes to metabolise lactose in the absence of glucose in bacteria
Describe how the lac operon works
In the presence of glucose, a repressor protein (produced by regulatory gene) is bound to the operator region
When lactose is present but glucose isn’t lactose binds to the repressor and releases it from the operator. Lactose is the inducer
This then allows RNA polymerase to bind to the promotor region and create the enzymes needed to metabolise Lactose
Lactose is metabolised
What is a transcription factor?
Proteins that act within a cells nucleus by binding to different promotor regions to express different genes in different cell types
They are needed because all cells in your body have the same genome, but different cells need to express it differently
What are introns and exons?
Introns are non-coding regions of DNA
Exons are the areas that code for something and are expressed
What is the name of the process where the introns are removed from the RNA strand?
Splicing
What is post-translational gene regulation?
Gene regulation that happens after transcription
Often involved the activation of proteins through phosphorylation
e.g the formation of cAMP from ATP
They often form transcription factors which then affect gene expression
What are homeobox gene sequences and what do the control?
Genes that control the anatomical layout of an organism and ensure that all the right body parts from in the right place
How did scientists realise that homeobox genes were important to development of organisms?
They compared the homeobox sequences in fruit flies and mice and they were very similar
What is the difference between How genes and Homeobox genes?
How genes are a type of Homeobox gene that is only found in animals
What do hox genes actually code for?
proteins that act in the nucleus as transcription factors
they can stimulate or inhibit: mitosis, apoptosis, cell migration and regulate the cell cycle
What is Hayflicks constant?
The number of times a cell can divide by mitosis before dying (about 50 times)
What is apoptosis?
Programmed cell death (cell suicide)
Describe the sequence of events in apoptosis
Enzymes break down cell cytoskeleton
Cytoplasm becomes dense with organelles
Surface membrane changes and blebs form
Chromatin condenses and nuclear envelope and DNA break down
Cell breaks into vesicles which are ingested by phagocytotic cells
Give an example of apoptosis in development of a human?
During limb development apoptosis causes the digits to separate from each other
Preventing tumors from forming
