cellular control - genetics Flashcards
define gene mutation
- a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
-many mutations occur in non- coding sections of DNA so have no effect on the sequence
three main ways that a mutation in the DNA base sequence can occur
-Insertion of one or more nucleotides
-Deletion of one or more nucleotides
-Substitution of one or more nucleotides
insertion
-when a nucleotide is randomly inserted into the DNA sequence
-changes the triplet codes= rest of amino acid sequence is fucked
deletion
-nucleotide is deleted, sequence and triplet codes are fucked
substitution
-a nucleotide is randomly swapped
-only changes a specific triplet code
3 forms of substitution mutations + description
silent mutation- does not alter the amino acid sequence as certain codons may code for same amino acid
missense mutation-alters a single amino acid in polypeptide chain e.g sickle cell anaemia
nonsense mutation-creates a premature stop codon (so stops translating the mRNA molecule into an amino acid sequence= affects the final protein structure e.g cystic fibrosis
example of a beneficial mutation
production of melanin
3 main types of regulatory mechanisms
Regulation at the transcriptional level (e.g lac operon)
Regulation at the post-transcriptional level
Regulation at the post-translational level
structural gene
codes for a protein that has a function within a cell (e.g. enzymes
regulatory genes
code for proteins (or various forms of RNA) that control the expression of structural genes
what is an operon
: a group or a cluster of genes that are controlled by the same promoter
-prokaryotes use operons to control the expression of genes
role of lac operon
WATCH VIDEO ON LAC OPERON AND BE ABLE TO LABEL
what are transcription factors
-proteins that bind to specific regions of DNA to control the transcription of genes
-eukaryotes also use transcription factors to express genes
transcription factors mechanism
-bind to the promotor region which either allows of prevents transcription taking place
-presence of transcription factor will either increase or decrease rate of transcription
name for coding and non coding sequences of DNA
Coding= exons, eventually translated into DNA
-Non coding= introns
-when transcription of a gene occurs, both exons and introns are transcribed=mRNA formed contains them
splicing
-introns must be removed from the pre-mRNA molecule as they shouldnt be translated
-exons are then all fused together to form a continuous mRNA molecule called mature mRNA that is ready to be translated
-ENSURES ONLY THE CODING SECTIONS OF mRNA ARE USED TO FORM PROTEINS
control at post transcriptional level
- polypeptides undergo modification in golgi or cytosol
-some polypeptides require activation vis cAMP = can activate enzymes
-
homeobox genes
-responsible for the genetic control of the development of body plans in different organisms
what is a homeobox
a DNA sequence that codes for a protein transcription factor
hox genes WATCH VIDEO
-subset of homeobox genes
-determine the identity of embryonic body regions along the anterior-posterior axis (i.e. the head-tail axis)
define mitosis and apoptosis
mitosis, identical cell division
apoptosis, natural cell death
steps leading to cell death/ apoptosis
-DNA becomes denser and more highly packed
-nuclear envelope breaks down and chromatin condenses
-vesicles form that contain hydrolytic enzymes
-phagocytes engulf the cell via phagocytosis
importance of mitosis and apoptosis in body plan development
-some cells that are produced (by mitosis) earlier on in development may no longer be needed
- e.g structures like fingers and toes first develop as a single combined unit and are then separated later via programmed cell death
the 2 groups that control mitosis
-Proto-oncogenes are genes that stimulate cell division
-Tumour-suppressor genes are genes that reduce cell division can also stimulate apoptosis
the role of cyclins and cyclin-dependant kinases in regulating the cell cycle
-Cyclins act as regulators
-CDKs act as catalysts (once activated by cyclins)
-e.g CDKs that have been activated by cyclins will catalyse the phosphorylation of particular target proteins, which can either activate or inactivate them
internal factors that trigger apoptosis in cell cycle
-rreparable genetic damage
-RNA decay
-Internal biochemical changes that lead to cell changes or cellular injury (e.g. oxidative reactions)
external factors that trigger apoptosis in cell cycle
-The presence of cell signalling molecules such as cytokines from the immune system, hormones and growth factors
-Viruses and bacteria, harmful pollutants or ultraviolet light
