Cellular control Flashcards
what’s a mutation
a random change to the genetic material
define mutagenic
factor that increases chance of mutation
what’s a gene mutation
change to DNA
are somatic mutations passed on to offspring
no, but those in meiosis are
what are the 2 ,main classes of DNA mutation
- point mutation: one base is substituted for another
- indel mutation: one or more nucleotides are inserted or deleted from a length of DNA, may cause a frameshift
what are the three types of point mutations
- silent
- missense
- nonsense
what are silent mutations
- change in triplet base, where that triplet still codes for the same aa so protein structure isn’t altered
- due to degeneracy of the genetic code
what are missense mutations
- change to the base triplet sequence that leads to a change in aa sequence in protein
- alteration to 1* structure leads to change 3*, altering shape + preventing usual function
what are nonsense mutations
- point mutations may alter a base triplet so that it becomes a termination triplet
- results in truncated protein that won’t function
- protein degraded in cell
what are indel (insertions and deletions) mutations
- if nucleotide base pairs ( not in multiples of 3) are inserted in or deleted from a gene, because the code is non-overlapping and read in triplets, all subsequent triplets are altered (frameshift)
- protein made can’t carry out function
- insertion or deletion of a triplet of base pairs result in loss or addition of an aa
what are expanding triplet nucleotide repeats
- some genes contain repeating triplets such as -CAG CAG CAG-
- no. of CAG triplets increases at meiosis and again from generation to generation
what are some benefits of mutations
- helped drive evolution through natural selection
- blue eyes useful for seeing in less bright light
- black skin has high conc of melanin protecting from sunburn + skin cancer
what are some neutral mutations
- inability to smell certain flowers
- differently shaped earlobes
define exon
the coding, or expressed, region of DNA
define intron
non-coding part of DNA
define operon
a group of genes that function as a single transcription unit
what’s 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 a gene
give an example of an operon in prokaryotic cells involved in the regulation of gene expression
lac operon
what can the bac E.coli metabolise instead when glucose isn’t present
lactose
what 2 enzymes does lactose induce the production of in E.coli
- lactose permease
- B galactosidase
what’s the lac operon
a length of DNA with an operator region next to the structural genes lac Z and lac Y that code for the 2 enzymes
relative positioning of structures in lac operon and what they are
I | |P|lac O |lac Z|lac Y
I = regulatory gene
P + lacO = control sites
P = promoter region
lacO = operator region
lac Y + lac Z = structural genes
what’s the role of lactose permease
allows lactose to enter the bacterial cell
what’s the role of B galactosidase
hydrolyses lactose to a glucose and B galactose
what’s the role of I (regulatory gene)
- codes for repressor protein (lacI) by producing mRNA which is translated into a protein by ribosome
role of repressor protein (lac I )
- when the gene is expressed, protein produced binds to operator region preventing RNA polymerase from binding to promoter region so lac Y and lac Z not transcribed
- enzymes not made, genes are “off”
how does the presence of lactose affect the repressor protein
- lactose bonds to lac I, altering its shape, preventing it from binding to operator
- RNA polymerase can bind to promoter region + transcribe structural gene into mRNA which is translated into the 2 enzymes
do all eukaryotic cells have the same genome
- yes, but different genes are expressed in diff cells for differentiation
- all the basic ‘housekeeping’ genes are expressed
- transcription factors slide along DNA molecule, binding to their promoter regions and either aid or inhibit the attachment of RNA polymerase to the DNA so activates or suppresses transcription of diff genes in diff cells
- involved in cell cycle, tumour suppressor genes regulate cell division, if it mutates it can lead to cancer
what’s involved in post-transcriptional gene regulation in eukaryotic cells
introns and exons
describe post-transcriptional gene regulation in eukaryotic cells
- all DNA of a gene including introns and exons is transcribed producing primary mRNA
- 1* mRNA is edited by removing RNA introns
- remaining mRNA exons are joined together
- endonuclease involved in editing + splicing
some introns may encode proteins and some may become…
short non-coding lengths of RNA involved in gene regulation
how can a length of a DNA encode more than one protein
depending on how its spliced
what’s involved in post-translational gene regulation in eukaryotes
- activation of proteins
- many enzymes are activated by being phosphorylated
outline the process of post-translational gene regulation in eukaryotes
- signalling molecule binds to a receptor on plasma membrane of target cell
- transmembrane protein activated which then activates a G protein
- activated G protein activates adenyl cyclase enzymes
- activated adenyl cyclase enzymes catalyse formation of many cAMP from ATP
- cAMP activates PKA
- activated PKA catalyses phosphorylation of proteins, hydrolysing ATP in the process
- PKA may phosphorylate another protein (CREB)
- this then enters the nucleus and acts as a transcription factor, regulating transcription
define apoptosis
programmed cell death
define conserved
has remained in all descendent species throughout evolutionary history
what’s the homeobox sequence
sequence of 180 base pairs ( excluding introns) involved in regulating patterns of anatomical development in animals, plants and fungi
what are hox genes
subset of homeobox genes, found only in animals, involved in formation of anatomical features in correct locations of body plan
what’s the homeodomain sequence
- 60 aa sequence encoded by 180 DNA base pairs
- can fold into a particular shape and bind to DNA, regulating transcription of adjacent genes
- contains 2 alpha helices connected by one turn (H-T-H)
how do hox genes control the body plan development in animals
- regulate the development of embryos along the head-tail axis
- control the position of body parts, helps form basic body pattern
- if these genes mutate, abnormalities occur
- controls polarity of organisms ( which end will develop into the head/tail)
what do hox genes encode
homeodomain proteins
how do homeodomain proteins act as transcription factors
- act on the nucleus and activate other genes that promote cell division, apoptosis and helps regulate cell cycle
are hox genes similar across different classes of animals
yes
what genes are hox genes regulated by
gap genes and pair-rule genes
which genes regulate mitosis
- homeobox and hox genes
- ensure that each daughter cell contains the full genome + is a clone of parent cell
- some genes are “switched off” so not expressed during differentiation
outline the process of apoptosis
- enzymes break down cytoskeleton
- cytoplasm becomes dense
- protrusions (plebs) form in the plasma membrane
- chromatin condenses, nuclear envelope breaks down and DNA breaks into fragments
- cell breaks into vesicles that are ingested by phagocytic cells, so debris don’t damage other cells or tissues
how is apoptosis controlled
- signalling molecules released when genes involved in regulating cell cycle and apoptosis respond to external or internal stimuli ( stress)
examples of signalling molecules involved in apoptosis
cytokines, hormones, growth factor, nitric oxide
why is apoptosis important
- causes digits to separate
- removes ineffective or harmful T-lymphocytes during development of immune system
why should rate of cells dying be equal to rate of cells produced by mitosis
- not enough apoptosis leads to tumours
- too much leads to cell loss + degradation
how is the right balance of rate of cells dying and rate of cells produced by mitosis achieved
through cell signalling
