6.1 Flashcards
What is a mutation
A random change to the genetic material, some mutations involve changes to the structure of the number of chromosomes
What is a gene mutation
A change to the DNA
When may mutations occur
Spontaneously during DNA replication before cell division,
What things can be mutagenic
Chemicals like tar in tobacco smoke, and ionising radiation like UV lights, x-rays and gamma rays
What does the structure of DNA make it
Stable and fairly resistant to corruption of the genetic information stored within it, but errors may still occur during the replication of a DNA molecule
What are mutations associated with mitotic division and what does this mean
Somatic mutations, so are not passed to offspring, they may be associated with the development of cancerous tumours
What mutations may be inherited by offspring
Mutations associated with meiosis and gamete formation may be inherited by offspring
What may gene mutations affect
Protein production and function
What are the 2 main classes of DNA mutation
Point mutation (one base pair replaces/substituted for another), insertion or deletion mutation (one or more nucleotides are inserted or deleted from a length of DNA, these may cause a frameshift
What does the genetic code consist of
Nucleotide base triplets within the DNA
What happens during transcription of a gene
this code is copied to a length of mRNA as codons, complementary to the base triplets on the template strand of the length of DNA, the sequence of codons on the mRNA is therefore a copy of the sequence of base triplets on the gene (coding strand of DNA)
What are the 3 types of point mutation
Silent, missense, nonsense
What does it mean that amino acids have more than one base triplets
This reduces the effect of point mutations as they don’t always cause a change to the sequence of amino acids in a protein (degeneracy)
what is a silent mutation
a point mutation involving a change to the base triplet, where the triplet still codes for the same amino acid
what is the result of a silent mutaion on a protein structure
the primary, 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 in a protein
what is the effect of a missense mutation
within a gene, this point mutation can have significant effects on the protein produced, it could alter the primary structure altering the secondary and tertiary structure preventing it carrying out its functions
what is sickle cell anemia caused by
the missense mutation, results in deoxygenated haemoglobin crystalising within erythrocytes, causing them to become sickle-shaped, blocking capillaries depriving tissue of oxygen.
what is a nonsense mutation
a point mutation what alters a base triplet to become a stop triplet
what are the effects of a nonsense mutation
it results in a truncated (shortened) protein that will not function, this abnormal protein will likely be degraded in the cells
what disease is caused by nonsense mutation
the genetic disease, Duchenne muscular dystrophy
what are indel mutations
mutations that cause a frameshift
what are the 2 indel mutation
insertion and deletion
what is a frameshift
if nucleotide base pairs (not in multiples of 3) are inserted in the gene or deleted from the gene, as the code is non-overlapping and reads in groups of 3 bases, all subsequent base triplets are altered.
what happens when mRNA is translated after insertion or deletion mutation
the amino acid sequence after the frameshift is disrupted, the primary sequence of the protein and the tertiary structure is much altered, so, the protein can’t carry out its normal function, if the protein was very abnormal it will be rapidly degraded within the cell
what do some forms of thalassaemia (haemoglobin disorder) result from
frameshift due to deletion of nucleotide bases
what may insertion or deletions of a triplet of base pairs result in
the addition/loss of an amino acid and not in a frameshift
what do some genes contain
a repeating triplet like CAG CAG CAG
what is expanding triple nucleotide repeats
the number of CAG (previous flashcard) triplets increases at meiosis and again from generation to generation
what is Huntington disease a result of
an expanding triple nucleotide repeat, if the number of repeating CAG sequences goes above a certain critical number, then the person with that genotype will develop Huntington disease later in life
are all mutations harmful
many are beneficial and driven evolution through natural selection, different alleles of a gene are produced through mutation
what are a neutral mutation and an examples
neither beneficial nor harmful like different shaped ear lobes.
how does regulation of gene expression at transcpiption level work in prokaryotic cells
enzymes that catalyse metabolic reactions involved in basic cellular functions are synthesised at fairly constant rates. Enzymes only needed in certain conditions are synthesised at varying rates according to need of cell
How does the bacterium E. coli normally metabloise glucose
as a respiratory substrate
what happens when glucose is absent in E. coli and dissacharide lactose is present
lactose induces production of 2 enzymes, lactose permease (which allows lactose to enter bacterial cells) and B-galactosidase (hydrolyses lactose to glucose and galactose)
what does the lac operon consist of
a length of DNA, about 6000 pairs long, containing an operator region lacO next to the structural genes lacZ and lacY that code for enzyme B-galactosidase and lactose permease
what is next to the operator region, lacO, in the lac operon
the promoter region, P, that RNA polymerase binds to begin transcription of structural genes lacZ and lacY
what are the operator region and promoter region in lac operon
the control sites
what is the definition of operon
a group of genes that function as a single transcription unit, first identified in prokaryotes.
what is found a small distance away from an operon
the regulatory gene, I, that codes for a repressor protein (LacI), when this regulatory gene is expressed, repressor protein produced binds to the operator, preventing RNA polymerase from binding to promoter region
what does the repressor protein produced by regulatory gene prevent
the genes lacZ and lacY from being transcribed(expressed), so enzymes for lactose metabolism is not made, the genes are ‘off’.
what are lacZ and lacY
structural gene
what is P and lac0
control sites
what is I in lac operon
regulatory gene
what happens when lactose is added to the cultural medium, once all the glucose has been used
molecules of lactose bind to the LacI repressor protein molecules altering the shape of LacI repressor protein, preventing it from binding to the operator, RNA polymerase molecule can then bind to the promotor region and begin transcribing structural genes into mRNA that is then translated into 2 enzymes, so lactose induces the enzymes needed to break it down.
what is the basis of cell differentiation in eukaryotic organsism
Every cell in a eukaryotic organism have the same genome, but as different cells use it differently, they function differently.
what are transcription factors
proteins, or short non-coding pieces of RNA, that act within the cells nucleus to control which genes in a cell is turned on or off
how do transcription factors work
they slide along a part of the DNA molecule, seeking and binding to their specific promoter regions, they then aid or inhibit the attachment of RNA polymerase to the DNA and activate or suppress transcription of the gene
what are transcription factors essential for
regulating gene expression in eukaryotes, making sure that different genes in different types of cells are activated or suppressed
what are some transcription factors involved in
regulating the cell cycle, tumour suppressor genes and proto-oncogenes help regulate cell division via transcription factors, mutations to these genes can lead to uncontrolled cell division or cancer.
why do many genes have their promoter regions some distance away along an unwound length of DNA
as when DNA coils, the promotor region may not be spatially far away
why do many genes have their promoter regions some distance away along an unwound length of DNA
as when DNA coils, the promotor region may not be spatially far away
what are introns
the non-coding region of DNA, these are not expressed
what are exons
the coding, or expressed, region of DNA
What happens to both intron and exon regions of DNA and what is the result
All DNA is transcribed. The resulting mRNA is then edited and the RNA introns (lengths corresponding to DNA introns) are removed. The remaining mRNA exons, corresponding to DNA exons are joined together
what is endonuclease
an enzyme that may be involved in the editing and splicing process of introns and exons
what do some introns do
encode proteins or some may become short non-coding lengths of RNA involved in gene regulation
what does it mean that some genes can be spliced in different ways
a length of DNA with its introns and exons can, according to how its spliced, encode more than one protein.
what does post-translational regulation of gene expression involve
the activation of proteins
how are many enzymes activated?
by being phosphorylated, cyclic AMP, cAMP, is an important second messenger involved in this activation
how does cAMP activate enzymes and can stimulate transcription (steps 1-4)
- a signalling molecule like glucagon, binds to a receptor on the plasma membrane of target cell 2. this activates a transmembrane protein which activates a G protein 3. the activated G protein activates adenyl cyclase enzymes 4. activated adenyl cyclase enzymes catalyse the formation of many molecules of cAMP from ATP
how does cAMP activate enzymes and can stimulate transcription (steps 5-8)
- cAMP activates PKA, protein kinase A 6. activated PKA catalyses the phosphorylation of various proteins, hydrolysing ATP in the process, this phosphorylation activates many enzymes in cytoplasm like those that convert glycogen to glucose 7. PKA may phosphorylate another protein (CREB, cAMP response element-binding) 8. this then enters the nucleus and acts as a transcription factor, to regulate transcription
what are homeotic genes involved in controlling
the anatomical development or morphogenisis of an organsim so that all structutres develop in the correct location, according to the body plan
what do serveral homeotic genes contain
homeobox sequences, sometimes called homeobox genes
what is each homeobox sequence
a stretch of 180 DNA base pairs (excluding introns) encoding a 60 amino acid sequence called homeodomain sequence, within a protein
what can the homeodomain sequence do
fold into a particular shape and bind to DNA, regulating the transcription of adjacent genes, these proteins are transcription factors and act within the cells nucleus
what is the name of the shape homeodomain-containing proteins fold into and what does it consist of
H-T-H, it consists of 2 alpha helices (H) connected by one turn (T).
what does part of the homeodomain amino acid sequence recognise
the TAAT sequence of the enhancer region (a region that initiates or enhances transcription) of a gene to be transcribed
What did scientists do in 1984
demonstrated that the homeobox sequence, first identified in 1983 in homeotic genes of fruit flys, also existed in mice. and the base sequence in these homeobotic sequences were similar in both species, informing scientists that these gene sequences are cruical for regulation of development and differentiation in organisms
also, what did Robertis discover in 1984
a subset of homeobox genes, Hox genes, in the africain clawed frog.
what did Robertis discovery in 1984 lead to
a new brancvh of biology called evolutionary development.
where are Hox genes found and where are Homeobox genes found
Hix found in onnly humans, homeobox genes found in animals, plants and fungi
What does molecular evidence indicate about homeobox genes
theyre present in Cnidaria meaning these genes arose before Palaeozoic era which began 541 milion years ago, befire bilateraly symmetrical organisms evolved
what does the molecular evuidence on homeobox genes indicate
that these genes first arose in an early ancestor which gave rise to each of these types of organisms and have been conserved, the sequences are alson simialr in all organsims studied and that extends across wide evolutionoary distances
what do the Hox genes regulate and control
the devlopment of embryos along the anterior-posterior (head-tail) axis, they control which body parts grow where
what happens if hox genes are mutated
abnormalities can occur like antennae can devlop as legs, or mammalian eyes developing on limbs
How are Hox genes arranged
in clusters and each cluster may contain up to 10 genes, in tetrapods (4 limbed vertebrae) including mammals there are 4 clusters. At some stage in evolution, the Hox clusters have been duplicated
whar are Hox genes doing in early embroyonic devlpoment
they are acxtive and expressed in order along the anterior-posterior axis of the developing embryo
what does the sequential and temporal order of Hox gene expression correspond to
the sequential and temporal development of various body parts, known as colinearity
what do Hox genes code and what do they do
homeodomain proteins that act in the nucleus as transcription factors and can switch on cascades of activation of other genes that promote miotic cell division, apoptosis, cell migration and regulate cell cycle
Are Hox genes similar across organisms how do we know this
yes, as a fly can function properly with a chicken Hox gene inserted in place of its own
How are Hox genes regulated
by other genes called gap genes and pair-rule genes. In turn, these genes are regulated by maternally supplied mRNA from the egg cytoplasm
How do you get from a zygote to embryo to fully formed adult
by many mitotic cell divisions
What is invoved in the part of the cell cycle where mitosis occurs
Homeobox and Hox genes help mitosis
what happens in cell differentiation
some genes in certain cells are switched off and not expressed
what did Hayflick show in 1962
normal body cells divide a limited number of times before dying
What did Kerr re-examine and researtch in 1965
the idea of programmed cell death (apoptosis)
how is apoptosis different from cell death due to trauma
cell death due to trauma involves hydrolytic enzymes
what are the first 3 steps of apoptosis
- enzymes break down the cell cytoskeleton 2. the cytoplasm becomes dense and tightly packed with organelles 3. cell surface membrane changes and small protrusion called blebs form
what are the last 2 steps of apoptosis
4, chromatin condenses, nuclear envelope breaks and DNA breaks into fragments 5. cell breaks into vesicles that are ingested by phagocytic cells, so cell debris doesn’t damage any other cells or tissues, the whole process happens quickly
how is apoptosis controlled
by many cell signals, some of these signalling molecules may be released by cells when genes that are involved in regulating the cell cycle and apoptosis respond to internal cell stimuli and external stimuli like stress
what are some examples of cell signalling molecules that control apoptosis
cytokines from cells of the immune system, hormones, growth factors and nitric oxide
what can nitric oxide induce and how
apoptosis by making the inner mitochondrial membrane more permeable to hydrogen ions and dissipating the proton gradient, proteins are released into the cytoplasm where they bind to apoptosis inhibitor proteins allowing apoptosis to occur
how is extensive proliferation of cell types prevented
by pruning through apoptosis, without release of any hydrolytic enzymes that could damage surrounding tissues
what does apoptosis cause during limb devlopment
causes digits to separate from each other
what can apoptosis do during immune system devlpoment
remove ineffective or harmful T-lymphocytes
what should the rate of cells dying equal
the rate of cells produced by mitosis
what does not enough apoptosis lead to
formation of tumors
what does too much apoptosis lead to
cell loss and degeneration
what plays a crucial role in maintaining the right amount of apoptosis
cell signalling
