Topic 6.1.1 Cellular Control Flashcards
What is the definition of a mutation?
- a change in the amount or arrangement of genetic material in a cell
- could be a chromosome change or a change in the nucleotide sequence of a gene
What are the different types of mutation?
- Spontaneous mutations
- Inherited mutations
- Induced mutations
- Gene (DNA) mutations
- Chromosome mutations
- Point mutations
What are spontaneous mutations?
- mutations caused by errors during DNA replication of gamete formation
What are inherited mutations?
- Mutations which are passed onto offspring through gametes
What are induced mutations?
- Mutations caused by mutagens such as mustard gas and radiation such as UV light and X-rays
What are gene (DNA) mutations?
- changes in nucleotide base sequence which lead to changes in genes
What are chromosome mutations?
- changes in parts of chromosomes or chromosome number
- occurs during meiosis and almost always harmful
What are point mutations?
DNA mutations in which:
- one nucleotide base pair is replaced by another (substitution)
- extra nucleotide base pairs are inserted into a length of DNA (insertion)
- nucleotide base pairs are deleted from a length of DNA (deletion)
What are the types of chromosomal mutations?
- deletion
- duplication
- translocation
- inversion
What happens during deletion?
- section of chromosome breaks off
What happens during duplication?
- sections duplicated
What happens during translocation?
- section breaks off and joins another non-homologous chromosome
What happens during inversion?
- section breaks off, is reversed, and joins back onto the chromosome
What types of mutations lead to frameshift?
- deletion
- insertion
What types of mutations can substitution cause?
- a missense mutation
- a silent mutation
- a nonsense mutation
What is a missense mutation?
- where a triplet code changes to a code for another amino acid
- one amino acid changed
What is a silent mutation?
- where a triplet code changes to a different code for the same amino acid
- no amino acid change
What is a nonsense mutation?
- where a triplet code for an amino acid changes to a code which instructs translation to stop
- amino acid changes to a stop codon
What type of mutation does insertion or deletion usually cause?
- a frame shift mutation
What is a frameshift mutation?
- where every triplet code after the point of insertion or deletion is altered, making a completely different protein
Mutations can be…
- neutral
- harmful
- beneficial
What are neutral mutations?
- mutations with no selective advantage or disadvantage
What are harmful mutations?
- mutations which decrease chances of survival
What are beneficial mutations?
- mutations which increase chances of survival
How can the environment effect whether a mutation is beneficial or harmful?
- dark skin in tropical climates –protects against damaging UV (contains melanin)
–less vitamin D needed in diet (synthesised through UV absorbed by skin) - pale skin in tropical climates – –loss of ability to make melanin (loss of protection from UV rays)
–pale skin burns and is prone to skin cancer - dark skin in temperate climate – –UV is not as intense meaning skin cannot synthesise vitamin D
–having a diet deficient in vitamin D matters
–leads to problems such as rickets and narrow pelvis - pale skin in temperate climates – –loss of melanin (loss of protection from UV)
–UV is not as intense but enough is still absorbed by skin
What is transcriptional control?
- genes can be turned on or off
What are some examples of transcriptional control?
- chromatin remodelling
- regulatory proteins + LAC operon
What is post-transcriptional control?
- mRNA can be modified which regulates translation and the types of proteins produced
What are some examples of post-transcriptional control?
- Cap and tail added to pre-mRNA
- splicing
- nucleotide modification
What is translational control?
- Translation can be stopped or started
What are some examples of translational control?
- binding of inhibitory proteins
- binding of initiation factors
- degradation of mRNA
What is post-translational control?
- proteins can be modified after synthesis which changes their function
What are some examples of post-translational control?
- addition of non-protein groups
- activation of protein kinases to add phosphate group
What are transcription factors, and what level of control are they involved in?
- proteins that bind to DNA and switch genes on or off by increasing or decreasing the rate of transcription
- transcriptional control
What are transcription factors called if they increase the rate of transcription?
- activators
What are transcription factors called if they decrease the rate of transcription?
- repressors
How do transcription factors work?
- transcription is initiated when proteins (transcription factors) bind to the promoter region of a gene
- this allows RNA polymerase to attach to the promoter region so that transcription begins
How is oestrogen an example of transcriptional control?
1- oestrogen passes through the cell membrane and enters into the cytoplasm
2- Oestrogen binds to the receptor on the transcription factor, causing a conformational change in its shape
3- it crosses the nuclear envelope and enters into the nucleus of the cell
4- This then binds to the promoter region of the gene, allowing RNA polymerase to join and transcription to occur
What are inducible enzymes?
- some enzymes are only synthesised in response to environmental changes
- these are called inducible enzymes
What is an example of an inducible enzyme?
- bacteria only makes enzymes to metabolise lactose if lactose is present in the medium they are growing on
- there would be no point in making enzymes to metabolise lactose if there isn’t any lactose to metabolise – making it would be both a waste of energy and a waste of amino acids
What inducible enzymes are made by bacteria to metabolise lactose and what do they do?
- Lactose Permease – transports lactose into the cell
- B-galactosidase – catalyses hydrolysis of lactose into glucose and galactose
- Transacetylase - adds acetyl groups to molecules
Lactose triggers the synthesis of three enzymes, making it a what?
- inducer
What is the Lac Operon?
- Synthesis of the three enzymes (lactose permease, B-galactosidase and transacetylase) is coded for and controlled by a length of DNA called the lac operon
- an operon is a length of DNA made up of structural genes, regulatory genes and control sites
What do structural genes on the Lac Operon do?
- code for proteins, such as enzymes
- Lactose Permease (increase lactose intake), B-galactosidase (to break down lactose), Transacetylase
What do regulator genes on the lac operon do?
- code for repressor proteins which are involved in switching transcription of structural genes on or off
What do the control sites on the lac operon do?
- (operator and promoter regions) are the sites where the regulatory protein binds to switch transcription of the structural genes on or off
What is the promoter region?
- binding site for RNA polymerase
What is the operator region?
- binding site for repressor protein
What is the role of cyclic AMP in the Lac Operon?
- the binding of RNA polymerase still only results in a relatively slow rate of transcription that needs to be increased or up-regulated to produce the required quantity of enzymes to metabolise lactose efficiently
- this is achieved by the binding of another protein cAMP receptor protein (CRP)
How does the Lac Operon work in the absence of lactose?
1) regulator gene is transcribed and translated to make the repressor protein
2) repressor protein binds to the operator and blocks promoter
3) RNA polymerase can’t bind to the promoter region so the structural genes can’t be transcribed
4) So B-galactosidase and lactose permease are not synthesised (it would be a waste of energy + amino acids to do so)
How does the Lac Operon work in the presence of lactose?
1) lactose binds to repressor protein – this changes shape so no longer binds to operator
2) RNA polymerase binds to promoter – structural genes are transcribed
3) mRNA from structural genes are translated
4) Cell makes lactose permease (to take lactose into the cell) and B-galactosidase (to hydrolyse lactose into glucose and galactose)
What happens in chromatin remodelling during transcriptional control?
- DNA wound around proteins called histones forms a DNA/Protein complex called a chromatin (heterochromatin is tightly wound DNA and Euchromatin is loosely wound DNA)
What happens in histone modification during transcriptional control?
- acetylation (the addition of acetyl groups) reduces the positive charge on the histones
- methylation (the addition of methyl groups) makes histones more hydrophobic
What is post-transcriptional control?
- mRNA can be modified which regulates translation and the types of proteins produced
- pre-mRNA is modified to form mature mRNA so it can bind to a ribosome and code for the synthesis of the required protein
What are the steps of post-transcriptional control?
1) a cap (modified nucleotide) is added to the 5’ end and a tail (long chain of adenine nucleotides) is added to the 3’ end – this stabilises the mRNA and delays degradation in the cytoplasm
2) Splicing occurs where the RNA is cut at specific points – the introns (non-coding DNA) are removed and the exons (coding DNA) are joined together
3) RNA editing can occur in which some mRNA molecules can be changed through base addition, deletion, or substitution, can synthesise different proteins with different functions from a single mRNA molecule or gene
What happens during translational control?
- regulating the process of protein synthesis
1) Degradation of mRNA – the more resistant, the longer it will last in the cytoplasm, the greater quantity of protein synthesised
2) Binding of inhibitory proteins to the mRNA preventing it from binding to ribosomes
3) Activation of initiation factors which aid the binding of mRNA to ribosomes
What happens during post-translational control?
- proteins can be modified after synthesis which changes their functions
- involves addition of non-protein groups such as carbohydrates
- modifying amino acids and the formation of bonds such as disulphide bridges
- folding or shortening of proteins
- modification by cAMP
What happens during post-translational control?
- proteins can be modified after synthesis which changes their functions
- involves addition of non-protein groups such as carbohydrates
- modifying amino acids and the formation of bonds such as disulphide bridges
- folding or shortening of proteins
- modification by cAMP
What is the regulation of the pattern of anatomical development called?
- morphogenesis
What are homeobox genes?
- codes for transcription factors (proteins) that regulate transcription by binding to the DNA for specific genes
What is the homeobox?
- a homeobox is a section of DNA 180 base pairs long coding for a part of the protein (transcription factors) 60 amino acids long, that is highly conserved
What does the homeobox code for?
- specific parts of the protein known as the homeodomain
What does the homeodomain do?
- binds to DNA to turn genes on or off
How does the complexity of an organism relate to its number of homeobox genes?
- the more complex an organism is, the more homeobox genes it has (humans = 44)
What do homeobox genes determine in organisms?
- polarity of the body (which end becomes the head and which becomes the tail)
- segmentation
- the position of different organs and limbs
What are Hox genes?
- group of homeobox genes only present in animals
- involved in the correct positioning of body parts in bilaterian (symmetrical body) animals
- expressed in early embryonic development
Where are Hox genes found in animals?
- clustered on chromosomes
What is apoptosis?
- programmed cell death that is important in immune response
What is the Hayflick constant?
- in multicellular organisms, cells die after 50 miotic divisions
Apart from after 50 miotic divisions, when do cells undergo apoptosis?
- during development
- if they threaten survival
What happens during apoptosis?
- a series of biochemical reactions
- cell contents are hydrolysed by enzymes
- they are then disposed of by phagocytes
How is damage to healthy cells limited during apoptosis?
- it occurs quickly
- hydrolytic enzymes are contained within the cell
- they are ingested by phagocytes meaning they are never released into surrounding tissue
Give four steps of apoptosis?
1) hydrolytic enzymes released from lysosomes inside the cell break down the cytoskeleton
2) Cytoplasm becomes dense - blebs form on cell surface membrane
3) Nucleus fragments and cell breaks into vesicles
4) Phagocytes ingest the vesicles (including hydrolytic enzymes)
