OCR Biology A - 6.1.1 - Cellular Control
The genetic code is universal, meaning the same codons specify the same amino acids in almost all organisms. It is a triplet code, where each codon of three bases codes for one amino acid.
Characteristics of genetic code
Universal
Triplet code
Degenerate
Non-overlapping
Key Terms
Characteristics of genetic code
Universal
Triplet code
Degenerate
Non-overlapping
Properties of DNA
Introns
Exons
Introns
Sections of DNA that do not code for a polypeptide
Regulatory sequences
Acts as a buffer for mutations
Regulatory sequences
Promoter regions
Terminator regions
Operator regions (prokaryotes)
Exons
Sections of DNA that code for polypeptides
Regulatory or structural genes
Regulatory genes
Genes that code for proteins used in DNA regulation
Related Flashcard Decks
Study Tips
- Press F to enter focus mode for distraction-free studying
- Review cards regularly to improve retention
- Try to recall the answer before flipping the card
- Share this deck with friends to study together
| Term | Definition |
|---|---|
Characteristics of genetic code | Universal Triplet code Degenerate Non-overlapping |
Properties of DNA | Introns Exons |
Introns | Sections of DNA that do not code for a polypeptide Regulatory sequences Acts as a buffer for mutations |
Regulatory sequences | Promoter regions Terminator regions Operator regions (prokaryotes) |
Exons | Sections of DNA that code for polypeptides Regulatory or structural genes |
Regulatory genes | Genes that code for proteins used in DNA regulation |
Structural genes | Genes that code for regular proteins |
Mutagens | Chemical, physical, or biological agents which cause mutations e.g. viruses (viral DNA inserts itself into the genome), radiation (Breaks one or both DNA strands) |
Where can genes be turned on or off | Transcriptional Post-transcriptional Translational Post-translational |
When does up/down regulation occur | Post trasncriptional Translational Post translational Either increases/ decreases rate of protein synthesis |
When are proteins modified | Translational Post translational |
Where are ribosomes assembled | Nucleolus |
Why is there a ribosomal groove | So mRNA can be read for transcription |
Types of mutations | Genes Chromosomal |
Point mutations | Mutations that occur at a spp point Insertion Substitution Deletion |
Effects of point mutations of proteins | Silent Missense Nonsense |
Insertion mutations | Addn. of one or more nucleotide base pairs into a DNA sequence |
Substitution mutation | Occurs when a base pair is substituted for another |
Deletion mutation | Occurs when a base pair is deleted from the DNA sequence |
Frameshift | A mutation caused by the addn. or deln. of a base pair(s) resulting in the translation of the genetic code from an unnatural reading frame from the point mutation to the end of the gene |
Silent mutations | Change in the DNA sequence that results to the change in nucleotide base pairs having no subsequent effect on on the amino acid produced May have occurrred in introns |
Missense mutations | A single nucleotide change leads to a different codon and therefore a different AA |
Nonsense mutations | Change in nucleotide sequence that leads to one of codons being converted to a terminator codon so the protein produced is truncated |
Class of mutations | Beneficial - depends on environment Neutral - No effect on chances of survival Disadvantageous - Causes genetic diseases, lessens chances of survival |
Histones | Basic proteins that associate w/ DNA in the nucleus and help to condense the DNA into a smaller volume Little balls in which DNA wraps around |
Chromatin | Complex of DNA and proteins that condense to form chromosomes within the nucleus of eukaryotic cells |
Euchromatin | Lightly packaged DNA; RNA polymerase can access the bases to transcribe the genes --> genes can be turned on |
Heterochromatin | Tightly packaged DNA; RNA polymerase cannot access the bases to transcribe the genes so they are turned off |
Promoter regions | Region of DNA that acts as the binding site for RNA polymerase to start transcription Intron Usually upstream |
Operator regions | Short region of DNA that is close to the promoter region | Interacts w/ regulatory proteins that controls the transcription of operons |
Downstream | To the right |
Upstream | To the left |
Operon | Functioning unit of DNA containing a group of structural genes expressed together Controlled by one promoter Only found in prokaryotes |
How is gene expression regulated in operons | Transcription factors bind |
Transcription factors | Coded for by regulatory genes Proteins which affects rate of transcription Activates or inhibits transcription of DNA by binding to promoter region w/ RNA polymerase or blocking the promoter region |
Repressor protein | A protein that binds to DNA/RNA inhibiting transcription by binding to the operator |
Gene expression | Production of proteins from a genome |
Control of gene expression | Whether genes are turned on or off |
Why is the control of gene expression necessary | In specialisation and differentiation of cells Increasing/ decreasing complexity Prevent vital resources being wasted |
Why is gene expression more complex on eukaryotes | Have to respond to changes in the internal and external environments Histones - DNA not exposed, genes expression is harder Prokaryotes don't have histones |
Housekeeping genes | Genes that code for proteins which are necessary for reactions in metabolic pathways and are constantly required (enzymes) |
Who has only exons | Prokaryotes and eukaryotes without jaw bones | Jaw boned eukaryotes have introns and exons |
Terminator region | Does not code for protein Regulatory site RNA polymerase is released to stop trancription |
RNA-coding sequence | Genes turn into mRNA | Has both introns and exons but introns are removed from premature mRNA during splicing to form mature mRNA |
Methods to regulate gene expression at transcriptional level | Histone modification | Transcription factors |
Histone modification | Histones are +vely charged and DNA. -vely charged --> attraction Modify charges to change degree of packaging Acetylation and phosphorylation reduce +ve charge so transcription happens Methylation increase +ve charge so transcription doesn't occur |
Transcription factors as a method of gene expression | Control rate of transcription by binding to spp DNA sequences Regulate genes to make sure they are expressed correctly Work alone or w/ others as an activator or repressor of RNA polymerase |
Regulating gene expression at the post transcriptional level | RNA processing RNA editing siRNA Happens simultaneously |
RNA processing | Pre-mRNA is modified --> mature-mRN A binds to ribosme and code for synthesis Adenine cap is added at 5' and tail at 3' Stabilises mRNA and delays degradation in cytoplasm, aids binding Splicing and the addn. of adenine cap and tail occur in the nucleus |
RNA editing | Some mRNA can be changed through base pair add., deln. or subn. Same effects as point mutations and results in synthesis of diff proteins w/ diff function s Increases range of proteins that can be produced from one mRNA strand |
Regulating gene expression at the translational level | Degradation of mRNA Binding of inhibitory proteins Protein kinases |
Degradation of mRNA | More resilient the molecule, the longer it lasts in cytoplasm, more translation |
Binding of inhibitory proteins | Occurs when protein is produced in wrong location or substrate is not available |
Regulation of gene expression at the post translational level | Protein activation - allows protein to carry out its function |
Protein activation | Occurs in Golgi Adding non protein groups e.g. carbs, phosphates Phosphorylation by protein kinases and ATP Folding/ shortening proteins (2' structure) Modification by cAMP |
Control sites | Operator region and promoter region |
Beta galactoside | An enzyme that catalyses the hydrolysis of lactose to glucose and galactose |
Lactose permease | A protein that transports lactose into the cell |
Lac i | Regulatory gene Codes for repressor protein (transcription factor) Always transcribed |
Lac p | Promoter region | Rna polymerase binds here |
Lac o | Operator region of control site Repressor protein binds here When lactose is present causes a conformational change in repressor protein allowing it to bind to lactose instead |
Lac z | Structural gene codes for beta galactoside |
Lac y | Structural gene that codes for lactose permease |
Lac operon | Inducible operon (only occurs when lactose is present from diffusion through lactose channels ) Example of transcriptional regulation Group of 3 genes involved in metabolism of lactose |
Mechanism of apoptosis | Cytoskeleton broken down by enzymes, loses function Cell shrinks and the membrane blebs, chromatin condenses Lysosomes release enzymes which break down cell components Cell breaks up into membrane-bound fragments Cell fragments are ingested and digested by phagocytic cells |
Uses of apoptosis | Morphogenesis - eliminating excess cells (webbed fingers) Selection - eliminates non functional cells Immunity - T killer eliminates dangerous cells (cancer) Organ size - eliminates excess cells Tissue remodelling - eliminates cells no longer need (breastfeeding) |
Somatic cell | Body cell |
Germ line cells | Gametes |
Germline mutations | Mutations in gametes so can cause genetic diseases and are passed on |
Somatic mutations | Not inherited but can cause ageing and cancer | Result of mutations in normal diploid cells |
Homeobox genes | Regulatory genes that contain a homeobox sequence (180 bp) Highly conserved in animals, plants and fungi Regulates mitosis and apoptosis in the embryonic stage Control body plans of an organism |
Homeotic genes | Set of genes that control morphology |
Homeodomain | Section of the protein coded for by the homeobox sequence (60 AA) |
Hox genes | Sub type of homeobox genes Only found in vertebrates and animals Found in clusters on chromosomes Controls body plans and morphology |
What do Hox genes code for | A group of TF's that controls expression of structural genes associated w/ the development of an organism's appendages during its embryonic stage to form a mature body plan |
What does a mutation of a Hox gene lead to | Diff body plan |
What ensures features are expressed correctly | Hox genes in a Hox cluster are activated in a particular order depending on where its found on the chromosome This matches order genes are expressed along H to T So structural genes are activated in a carefully coordinated sequence |
Why are Hox genes highly conserved | V. important Mutations alter body plans Mutations are selected against |
Polypeptides that control the physical development of an organism | Structural proteins Enzymes used in metabolic pathways Hormones Receptor proteins |
Protein kinases | Activated by cyclic AMP and activate proteins through phosphorylation using ATP |
siRNA | Small interfering RNA - only needed when cell has made sufficient protein Complementary base sequence to mRNA that's to be degraded Binds to mRNA and activates an enzyme that breaks it down RNA nucleotides recycled to nucleus |