Cellular control Flashcards
mutation-
gene mutation-
-random change to genetic material
-change to DNA
Types of mutation
-point: silent, missense, nonsense
-indel: insertion, deletion
3 types of point mutation
-silent- change in base triplet that codes for the same amino acid
-missense- change in base triplet that leads to a change in the amino acid
-nonsense- change in base triplet that codes for a stop triplet, this results in a truncated protein that won’t function
Indel mutation
-cause a frameshift if not inserted or deleted in multiples of 3
-this therefore alters the primary structure which therefore alters the tertiary structure
-so protein can’t carry out normal function
Expanding triple nucleotide repeats
-genes have repeating triplet eg. CAG CAG
-in ETNR the number of CAG triplets increase at meiosis from generation to generation
-this causes Huntington’s disease
Not all mutations harmful
-some beneficial eg. evolution, natural selection
-eg. blue eyes could be harmful in sunny areas as could cause cataracts. but in temperate zones allows people to see better
-some mutations are neutral eg. different shaped ear lobes
Regulation of gene expression at transcriptional level
Lac operon
-promoter region (control site) which is where RNA polymerase binds
-lac O = operator region (control site) where repressor protein binds
-lac Z = structural gene which codes for B galactosidase
-lac Y = structural gene which codes for lactose permease
-separate to lac operon is regulatory gene which codes for repressor protein
E coli in presence of glucose
-regulatory gene produces repressor protein
-this binds to the operator, preventing RNA polymerase from binding to promoter region
-this prevents lac Z and lac Y from being transcribed so enzymes for lactose metabolism aren’t made
-this is because the E coli can respire the glucose, so no amino acids and energy are wasted
E coli in presence of lactose
-regulatory gene produces repressor
-lactose (inducer) binds to the repressor, changing its shape
-the repressor can no longer bind to operator
-this means RNA polymerase can bind to the promoter region and can transcribe the structural genes into mRNA
-this is translated into the 2 enzymes
-this break down lactose to glucose + galactose so E coli can respire glucose
lactose permease-
B galactosidase-
-allows lactose to enter the bacterial cell
-hydrolyses lactose to glucose + galactose
Regulation of gene expression at the transcriptional level in eukaryotes
-transcription factors slide alongside DNA molecule
-these then bind to promoter regions
-these transcription factors can either aid or inhibit the attachment of RNA polymerase
-this therefore activates or supresses transcription of gene
Transcription factors-
-proteins, short non-coding pieces of RNA
Intron-
Exon-
-non-coding region of DNA/RNA
-coding or expressed region of DNA/RNA
Post-transcriptional gene regulation
-all DNA transcribed producing primary mRNA
-primary mRNA is edited and introns removed
-the remaining exons join together producing mRNA
-this is catalysed by restriction enzymes that are involved in the editing and splicing
-some introns may encode proteins and some may become short non-coding lengths of RNA (transcription factors)
Post translational level of gene regulation
-signalling molecule eg. glucagon binds to receptor on membrane
-this activates G protein
-this activates adenyl cyclase
-catalyses formation of cAMP from ATP
- cAMP activates protein kinase A (PKA)
-PKA catalyses phosphorylation of proteins, hydrolysing ATP to ADP in the process
-PKA may phosphorylate another protein eg. CREB
-this enters nucleus and acts as transcription factor
Morphogenesis
the process that causes an organism to form its shape which is caused by homeotic genes
Homeotic genes
-control anatomical development/ morphogenesis or an organism
-within them is a homeobox sequence which has 180 base pairs, codes for 60 amino acids
-the homeobox sequence codes for a homeodomain sequence
-highly conserved as are crucial for the development of organisms. Therefore they remain unchanged throughout evolution of different descendent species
Homeodomain sequence
-folds into specific shape and acts as transcription factor
-3 alpha helices
-2 form a helix turn helix where two alpha helices are connected by one turn of amino acid sequence
Hox genes
-type of homeobox gene only found in animals (code for homeodomain that acts as transcription factor)
-regulate development along the anterior-posterior (head-tail) axis
-arranged in clusters, next to each other on the chromosome
-homeotic mutation- hox gene mutation that causes body parts to develop at wrong place
-expressed in early embryonic development
-spatial linearity- order of genes on the chromosome match the expression patterns along the embryo
-temporal linearity- expression of genes occur in an order, starting with anterior (head) followed by middle then tail (posterior)
Apoptosis
-enzymes break down cell cytoskeleton
-cytoplasm becomes dense with tightly packed organelles
-cell surface membrane changes and small protrusions called plebs form
-chromatic condenses, nuclear envelope breaks, DNA breaks into fragments
-cell breaks into vesicles that are ingested by phagocytes
Control of apoptosis
-cell signals eg. cytokines, hormones, growth factors or nitric oxide
-nitric oxide makes inner mitochondrial membrane more permeable to H+, so no proton gradient. This releases proteins to cytoplasm which bind apoptosis inhibitor proteins, so apoptosis occurs
Importance apoptosis
-limb development as separates digits
-removes harmful T lymphocytes during development of immune system
Rate of apoptosis equal to mitosis
-prevents formation of tumours
-prevents cell loss and degeneration
How are hox genes regulated
-regulated by gap genes and pair-rule genes
-these genes regulated by maternally supplied mRNA from egg cytoplasm
