Cellular Control Flashcards
Define mutation
A change in the genetic material which may affect the phenotype of the organism
Define point mutation
Changes one base in the triplet codon-may or may not have damaging effects
Define substitution
A mutation where one or more nucleotides are substituted for another in a DNA strand
Define deletion
Mutations where one or more nucleotides are deleted and lost from the DNA strand
Define insertion
A mutation where one or more extra nucleotides are inserted into a DNA strand
Define frame shift
- The deletion or insertion of a nucleotide or nucleotides leads to a frame-shift mutation.
- It shifts the reading frame of the sequence of bases, it will change every successive codon from the point of mutation
Define silent mutation
A mutation that occurs in the part of a gene that does not code for a protein therefore it will not affect the phenotype.
Define nonsense mutation
- Result in a codon becoming a stop codon instead of coding for an amino acids.
- The result is a shortened protein being synthesised which is normally non-functional
Define misense mutation
- Result in the incorporation of an incorrect amino acid/acids into the primary structure when the protein is synthesised.
- The mutation could be silent, beneficial or harmful
Define gene mutation
Gene mutations occur in single genes or sections of DNA
Define chromosome mutation
- Chromosome mutations affect the whole chromosome or number of chromosomes within a cell.
Explain why a change in the sequence of nucleotides of a gene can affect the function of the protein produced from that gene.
- A change in a base sequence may change the amino acid the codon codes for.
- This leads to changes in the primary structure of the protein.
- But as it is degenerate it may mean the new codon still codes for the same amino acid so no change to protein.
Describe how a mutation can have a neutral effect, a harmful effect or a beneficial effect, and give an example of each
- Neutral- no effect on the phenotype of an organism because normally functioning proteins are still synthesised
- Harmful- the phenotype of an organism is affected in a negative way because proteins are no longer synthesised or proteins synthesised are no longer functional.- interfere with essential processes.
- Beneficial- proteins is synthesised so it has new and useful characteristics in the phenotype.- e.g immunity to HIV from proteins in cell surface membrane
State the 3 types of mutagen and give an example of each
- Physical- ionizing radiation such as x-rays- break one or both DNA strands
- Chemical- Deaminating agents- chemically alter bases in DNA
- Biological agents
a) Alkylating agents- methyl or ethyl groups are attached to bases- results in incorrect base pairing
b) Base analogs- incorporated into DNA in place of the usual bases in replication
c) Viruses- viral DNA may insert itself into a genome
Name and describe the 4 types of chromosome mutation
- Deletion- a section of chromosomes breaks off and is lost within the cell
- Duplication- sections get duplicated on a chromosomes
- Translocation- a section of one chromosome breaks off and joins another non-homologous chromosome
- Inversion- a section of chromosome breaks off, is reversed and then joins back onto the chromosome
Describe and explain the possible effects of a substitution mutation.
- It changes the codon so if the new codon codes for a different amino acid this will leas to change in proteins
- But it may not as it is degenerate
Describe and explain the possible effects of insertion or deletion mutations
- The insertion or deletion of a nucleotide or nucleotides leads to a frameshift mutation.
- It changes every successive codon from the point of mutation
Define gene expression
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. - often proteins
Define epigenetics
External control of genetic regulation
Name and describe the four levels at which genes (or proteins) are regulated
- Transcriptional- genes can be turned on or off
- Post-transcriptional- mRNA can be modified which regulates translation and types of proteins produced
- Translational- translation can be stopped or started
- Post-translational- proteins can be modified after synthesis which changes their functions
Define chromatin
Uncondensed DNA in a complex with histones
Define heterochromatin
Tightly packed DNA causing chromosomes to be visible during cell division
Define euchromatin
Loosely packed DNA present during interphase
Describe how chromatin remodelling allows the expression of some genes but not others.
- The transcription of genes is not possible when DNA is tightly wound because RNA polymerase cannot access the genes.
- The genes in euchromatin can be freely transcribed
- Proteins synthesis does not occur during cell division as it is heterochromatin but it does during interphase between cell divisions as it is euchromatin
- This is a simple form of regulation that ensures the proteins necessary for cell division are synthesised in time.
- It also prevents the complex and energy-consuming process of protein synthesis form occurring when cells are actually dividing.
Describe how histone modification can affect gene expression
- DNA coils around histones because they are positively charged and DNA is negatively charged
- Histones can be modified to increase or decrease the degree of packing (or condensation)
- The addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduces the positive charge on the histones and this causes DNA to coil less tightly allowing certain genes to be transcribed.
- The addition of methyl groups (methylation) makes histones more hydrophobic so they bind more tightly to each other causing DNA to coil more tightly and preventing transcription of genes.
Define the term “operon”
Group of genes expressed together- they are under control of the same regulatory mechanism
Draw and label a diagram to show the lac operon and its associated regulatory gene.
- Regulatory gene- lacIgene which makes repressor protein (not part of operon)
- Promoter- site of RNA polymerase binding
- Operator- allows the genes to be turned on or off, depending on binding of a repressor protein
- Structural genes needed to metabolise lactose
- protein 1- lac Z
- protein 2-lac Y
- protein 3- lac A
Define the term “structural gene”
Genes that code for structural proteins or enzymes not involved in DNA regulation
Name the proteins produced from the structural genes in the lac operon.
- Protein 1- lac Z- Beta galactosidase- breaks down lactose
- Protein 2- lac Y- Lactose permease- brings lactose into cell
- Protein 3- lac A- Transacetylase- unknown function
Describe the roles of the regulatory gene, the structural genes the lac operon for the metabolism of lactose.
- lac I is a regulatory gene- located near to the operon and codes for a repressor protein that prevents the transcription of the structural genes in the absence of lactose
- Structural genes- code for three enzymes which are transcribed onto a single long molecule of mRNA but are translated into the 3 enzymes
When is lactose used as a respiratory substrate for Escherichia coli
- Glucose is easier to metabolise and is the preferred respiratory substrate.
- If glucose is in short supply, lactose can be used as a respiratory substrate.
- Different enzymes are needed to metabolise lactose
Explain how the lac operon works when lactose is absent from the growth medium
- The repressor protein is constantly being produced and binds to an area called the operator
- The binding of this protein prevents RNA polymerase binding to DNA and beginning transcription. - down regulation
- The section of DNA that is the binding site for the RNA polymerase is called the promoter
Explain how the lac operon works when lactose is present in the growth medium
- When lactose is present, it binds to the repressor protein causing it to change shape so it can no longer bind to the operator.
- As a result RNA polymerase can bind to the promoter, the 3 structural genes are transcribed and the enzymes are synthesised.
Describe the role of cAMP in control of the lac operon.
- The binding of RNA polymerase still only results in a relatively slow rate of transcription that needs t 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)- only possible when CRP is bound to cAMP
- The transport of glucose into an E.Coli cell decreases the levels of cAMP, reducing the transcription of the genes responsible for the metabolism of lactose.
- If both glucose and lactose are present then it will still be glucose that is metabolised.
Define intron
Regions of non-coding DNA or RNA
Define exons
Regions of coding DNA or RNA
Define pre mRNA
The mRNA transcribed from the DNA before any post-transcriptional regulation to remove introns
Define mature mRNA
mRNA after the removal of introns and any other post-transcriptional changes
Define RNA processing
RNA processing refers to any modification made to RNA between its transcription and its final function in the cell.
Define RNA editing
- When the nucleotide sequence of mRNA molecules are changed through base addition, deletion or substitution.
- Same effect as point mutations and can result in the synthesis of different proteins- increases the range of proteins that can be produced from a single mRNA molecule or gene
- A type of RNA processing
Describe how pre-mRNA is modified to produce mature mRNA, where this occurs and the benefit of this modification process.
Post-transcriptional/ pre-translational control
- A cap (modified nucleotide) is added to the 5’ end and a tail (a long chain of adenine nucleotides) is added to the 3’ end.
- These both help to stabilise mRNA and delay degradation in the cytoplasm
- The cap also aids binding of mRNA to ribosomes.
- Splicing occurs where the RNA is cut at specific points- the introns are removed and the exons are joined together. Both processes occur in the nucleus.
Describe 3 mechanisms that can regulate protein synthesis at the translational level.
- Degradation of mRNA- the more resistant the molecule the longer it will last in the cytoplasm- greater quantity of protein synthesised.
- Binding of inhibitory proteins to mRNA- prevents it binding to ribosomes and the synthesis of proteins
- Activation of initiation factors which aid the binding of mRNA to ribosomes
Describe the role of protein kinases in regulation of gene expression or protein activity
- Enzymes that catalyse the addition of phosphate groups to proteins
- The addition of a phosphate group changes the primary structure and so the function of a protein
- Many enzymes are activated by phosphorylation.
- Protein kinases are therefore important regulators of cell activity
- Protein kinases are themselves often activated by the secondary messenger cAMP.
Describe 4 ways in which proteins can be modified to provide post-translational control.
Involves modifications to the proteins that have been synthesised.
- Addition of non-protein groups such as carbohydrate chains, lipids or phosphates
- Modifying amino acids and the formation of bonds such as disulfide bridges
- Folding or shortening of proteins
- Modification by cAMP- e.g in lac Operon cAMP binds to cAMP receptor protein
Define body plan
The basic shape of members of an animal phylum; the general structure each individual organism assumes as it develops.
Define morphogenesis
The regulation of the pattern of anatomical development
Define homeobox gene
Genes responsible for the development of body plans.
Homeotic/regulatory gene contains the homeobox sequence that codes for the homeodomain .
Define homeodomain
A conserved motif of 60 amino acids found in all homeobox proteins. It is the part of the protein that binds to DNA allowing the protein to act as a transcriptional regulator
Define Hox genes
A group of homeobox genes that are only present in animals
Name the 3 kingdoms which all have very similar homeobox genes.
Plants, animals and fungi
Define the term “highly conserved”.
Highly conserved- very similar
Describe the role of Hox genes in controlling the body plan of animals
- They are responsible for the correct positioning of body parts
- In animals the Hox genes are found in gene clusters- mammals have 4 clusters on different chromosomes
- The order in which the genes appear along the chromosomes is the order in which their effects are expressed in the organism
- Humans have 39 Hox genes in total that are believed to have originated from one from one ancient homeobox gene
Describe the layout of living organisms
- Body plans are usually represented as cross-sections through the organisms showing the fundamental arrangement of tissue layers
- Diploblastic animals- 2 primary tissue layers
- Triploblastic animals- 3 primary tissue layers
- All animals are segmented- the segments have multiplied over time and are specialised to perform different functions
- Hox genes in the head control the development of mouth-parts
- Hox genes in the thorax control development of wings, limbs or ribs
- The individual vertebrae and associated structures have all developed from segments in the embryo called somites which are directed by Hox genes to develop in a particular way depending on their position in the sequence
What are the different types of symmetry in animal body shape
- Radial symmetry- seen in diploblastic animals- no right or left sides only a top or bottom e.g. jellyfish
- Bilateral symmetry- most animals- have both right and left sides and a head and a tail rather than just a top and bottom
- Asymmetry- sponges- no lines of symmetry
Define apoptosis
Programmed and controlled cell death important in controlling the body form and in the removal of damaged or diseased cells
Outline the process of apoptosis.
- Similar to sculptor and wood
- The shape is revealed as material is removed bit by bit- removes unwanted cells and tissues to shape different body parts
- Cells undergoing apoptosis can also release chemical signals which stimulate mitosis and cell proliferation leading to the remodelling of tissues
- Regulated by Hox genes
Describe the steps in the process of apoptosis
- Enzymes inside the cell break down important cell components such as proteins in the cytoplasm and DNA in the nucleus
- The cell’s contents are broken down it begins to shrink and the nucleus condenses and the cell forms blebs
- Proteins start to breakdown the cell compartments and enzymes break down the nucleus
- The DNA fragments
- The cell fragments are engulfed by phagocytes and digested.
Explain how apoptosis is controlled
- Hox genes regulate apoptosis and mitosis
- During development, genes that control apoptosis and genes that control mitosis are switched on or off in appropriate cells
- This means some cells die, whilst some new cells are produced and the correct body plan develops
Describe the role of mitosis and apoptosis in growth and development
- Mitosis and differentiation create the bulk of body parts and then apoptosis refines the parts by removing unwanted structures
Define the term “stress” in relation to homeostasis and describe the factors that may influence the rate of mitosis or apoptosis.
- The expression of regulatory genes can be influenced by the environment, internal and external
Stress can be defined as the condition produced when the homeostatic balance within an organism is upset - An internal stimulus could be DNA damage- if detected during cell cycle this can result in the expression of genes which cause the cycle to be paused and can even trigger apoptosis
- An external stimulus-lack of nutrient availability- could result in gene expression that prevents cells from undergoing mitosis. Attack by pathogen leads to apoptosis.
