Chapter 6.1- Cellular Control Flashcards
What is a mutation?
- random change to the genetic material
- some mutations involve changes to the structure or number of chromosomes.
What is a gene mutation?
change to the DNA
What chemicals are described as being mutagenic(physical or chemical agent that changes that changes the genetic material?
- tar in tobacco smoke
- ionising radiation such as UV light, X-rays and gamma rays
What type of mutations are not passed onto offspring and give an example?
- mutations associated with mitotic divisions which are somatic (any cell other than reproductive cells) mutations
- development of cancerous tumours
What type of mutations are passed onto offspring?
-mutations involved with meiosis and gamete formation may be inherited by offspring
What are point mutations?
one base pair replaces(is substituted) for another
What are insertion or deletion (indeed) mutations?
one or more nucleotides are inserted or deleted from a length of DNA. They may cause a frameshift
What are the three types of point mutation?
- silent
- missense
- nonsense
What is a silent mutation?
- this is where there is a change to the base triplet, where that triplet still codes for the same amino acid
- the primary structure of the proteins and therefore the secondary and tertiary structure, is not altered.
What is a missense mutation?
- a change to the base triplet sequence that leads to a change in the amino acid sequence
- this may have a significant effect on the protein produced. The alteration to the primary structure leads to a change to the tertiary structure of the protein, altering its shape and preventing it from carrying out its usual function
What disease arises from a missense mutation?
Sickle cell anaemia as the sixth base triplet of the gene for the beta-polypeptide chains of haemoglobin:the amino acid valine, instead of glutamic acid, is inserted at this position. This results in deoxygenated haemoglobin crystallising within erythrocytes, causing them to become sickle shaped, blocking capillaries and depriving tissues of oxygen
What is a nonsense mutation?
- A point mutation that becomes a termination(stop) triplet.
- this particularly disruptive point mutation results in a truncated protein that will not function. This abnormal protein will most likely be degraded within the cell
What genetic disease arises from a nonsense mutation?
Duchenne muscular dystrophy
What are insertion and deletion mutations(indel)?
when nucleotide bases, not in multiple threes, are inserted in the gene or deleted from the gene, because the code is non-overlapping and read in groups of three bases, all the subsequent base triplets are altered. This is known as a frameshift.
-the primary structure of the protein, and subsequently the tertiary structure, is much altered.
What disorder is caused by a insertion or deletion(indeed) mutation?
some forms of thalassaemia, a haemoglobin disorder, results from frameshift due to deletions of nucleotide bases
What type of insertion and deletion (indeed) mutations do not cause a frameshift and degradation of the protein?
insertion or deletions of a triplet of base pairs results in the addition or loss of an amino acid
What are expanding triple nucleotide repeats?
the number of the same triplet increases at meiosis and again from generation to generation, such as -CAG CAG CAG
What disease is caused by expanding nucleotide repeats?
- Huntington’s disease
- if the number of CAG sequences goes above a certain critical number, then the person with that genotype will develop the symptoms of Huntington’s disease later in life
What are two examples of advantageous mutations?
- blue eyes arose in the population 6000-8000 years ago. In more temperate zones, it could enable people to see better in less bright light
- In Africa, humans had black skin, as this meant that they had high concentrations of melanin protecting them from sunburn and skin cancer. In more temperate areas a paler skin would be an advantage, enabling vitamin D to be made with a lower intensity of sunlight. Vitamin D protects us from rickets, heart disease and cancer.
What are the two enzymes that are produced as a result of being induced by the present of lactose?
- lactose permease, which allows lactose to enter the bacterial cell
- Beta-galactosidase, which hydrolyses lactose to glucose and galactose
What typeof gene regulation is the lac operon an example of?
regulation at the transcriptional level
What are the different parts of the lac operon and what are they in oder from left to right?
- regulatory gene (I)
- promoter region(p)
- operator region (lacO)
- structural gene (lac Z)
- structural gene (lac Y)
What are the steps in the regulation of gene expression at the transcriptional level regarding the bacterium E.coli?
- when lactose is added to the culture medium, once all the glucose has been used, molecules of lactose bind to the LacI repressor protein molecules; this alters the shape of the LacI repressor protein, preventing it from binding to the operator.
- RNA polymerase enzyme can then bind to the promoter region and being transcribing the structural genes into mRNA and then will be translated into the two enzymes (lactose permeate and beta-galactosidase.
What is the gene that codes for the repressor protein (LacI) which binds to the operator region when glucose is present?
regulatory gene I
What is a transcription factor?
protein or short non-coding RNA that can combine with a specific site on a length of DNA and inhibit or activate transcription of the gene
What are introns?
the non-coding region of DNA
What are exons?
the coding, or expressed, region of DNA
What happens during ‘splicing’ of primary mRNA into secondary mRNA as a result of post-transcriptional gene regulation?
- all the DNA of a gene is transcribed (both introns and exons) is transcribed. The rustling mRNA is is called primary mRNA.
- introns ar removed from the length of DNA and the exons are all joined together with the help of the enzyme endonuclease
What is meant by the post-translational level of gene regulation?
involves the activation of proteins and often involves phosphorylation
What are the steps in the activation of proteins (post-translational gene regulation)?
- signalling molecule, e.g. the hormone glucagon, bind to a receptor on the plasma membrane of the target cell
- this activates a G protein
- activated G protein will activated adenyl cycle enzymes
- these molecules then catalyse the formation of many molecules of cAMP from ATP.
- cAMP activates PKA (protein kinase A)
- these activated molecules then catalyse the phosphorylation of various proteins, hydrolysing ATP in the process.
- PKA may phosphorylate another protein (CREB,cAMP response element binding)
- this then enters the nucleus and acts as a transcription factor, to regulate gene expression
What are homeotic genes?
large and ancient family of genes, that are involved in the controlling the anatomical development, or morphogenesis, of an organism, so that all structures develop in the correct location, according to their body plan
What are homeobox sequences?
sequence of 180 bare pairs (including introns) found within genes that are involved in regulating patters of anatomical development in animals, fungi and plants
How many DNA base pairs are there in homeobox sequences and how many amino acids are therefore coded for and whats the name of this sequence?
- each homeobox sequence is a stretch of 180 DNA pairs
- this encodes a 60-amino acid sequence, which is called a homeodomain sequence
How does the homeodomain sequence act as a transcription factor?
-it can fold into a particular shape and bind to DNA, regulating the transcription of adjacent genes
What is the shape of a homeodomain transcription factor?
- H-T-H
- consists of 2 alpha-helixes (H) connected by one turn (T).
What are Hox genes?
subset of homeobox genes, found only in animals;involved in the formation of anatomical features In current locations of body plan
Where are homeobox and Hox genes found?
- homeobox genes are found in plants, fungi and animals
- Hox genes are a subset of homeobox genes and are only found in animals
What is the specific name of the area in which hox genes regulate the development of embryos?
anterior-posterior(head-tail) axis
How are Hox genes arranged in animals?
they are arranged in clusters and each cluster may contain up to 10 genes
What is colinearity?
sequence and timing of expression of each gene cluster corresponds with the sequential and temporal development of body parts
What is the hayflick constant?
normal body cell can only divide a limited number of times (around 50 times)
What is meant by apoptosis?
programmed cell death
What are the sequence of events in apoptosis?
- enzymes break down the cell cytoskeleton
- cytoplasm becomes dense with tightly packed organelles
- the cell surface membrane changes and small protrusions called blebs form
- chromatin condenses, the nuclear envelop breaks and DNA breaks into fragments
- the cell breaks into vesicles that are ingested by phagocytic cells, so that cell debris does not damage any other cells or tissues. The whole process happens very quickly
What triggers apoptosis?
happens when genes regulating the cell cycle respond to stimuli e.g. hormones, growth factors and nitric oxide (NO)
Why is apoptosis important?
- during limb development, apoptosis causes the digits to separate from each other
- apoptosis removes harmful T-lymphocytes from the body during the early development of the immune system
What happens if the rate of apoptosis is greater than the rate of mitosis?
leads to cell loss and degeneration
What happens is the rate of apoptosis is less than the rate of mitosis?
leads to formation of tumours
