Chapter 19 Genetics Of Living Systems Flashcards
What is a mutation?
A change in the amount or the structure of DNA in an organism
What is a gene mutation?
A change in the nucleotide (base pair) sequence of single genes or small sections of DNA
What is a chromosome mutation?
A change in several genes that can affect portions
of a chromosome or numbers of chromosomes in a cell.
What is a gene point mutation?
A mutation that happens to one base
What causes mutations in genes?
The change in the sequence of bases can be caused by:
Substitution
Deletion
Insertion
What is substitution in gene mutation?
Changes a base in the codon sequence
What is the affect of substitution?
Misense- if the substitution results in a new codon that codes for a different amino acid sequence resulting in the synthesis of a different protein.
Nosense- the substitution results in a new codon that codes for a stop codon
Silent- due to the degenerative nature of the genetic code this means that the new codon could still code for the same amino acid and therefore have no effect on the sequence or the protein synthesised.
What is insertion in gene mutation?
A base is added to the sequence
What is deletion in gene mutation?
A base is removed from the sequence
What is the affect of insertion and deletion?
Insertion and deletion can cause frameshift mutation where the mutation changes the reading frame of the codon. This alters every successive codon from the point of mutation.
This changes the amino acid which is coded for and therefore the protein synthesised.
When does insertion or deletion have no effect on the reading frame of the codon?
When the number of bases changed are multiples of three as they correspond to full codons and the reading frame does not shift.
However, the protein synthesised will still be altered as the amino acids have changed.
What are the effects of mutations?
-No effect on the phenotype of an organism
-Damaging- the phenotype is affected negatively as proteins are no longer synthesised or proteins are non-functional.
-Beneficial- a different protein structure is synthesised which is advantageous to the phenotype
What is an example of a neutral mutation?
Dimples
Free/ attached ear lobes
What is an example of a damaging mutation?
Cystic fibrosis
Sickle cell anaemia
Colour blindness
What is an example of a beneficial mutation?
Lactose persistence
HIV resistance
Bacterial antibiotic resistance
What are Mutagens?
A chemical, physical or biological agent which increases the risk of mutation rates.
What are causes of mutation?
-Mutagens
-The loss of a purine or pyrimidine base can result in the replacement of the incorrect base
-Free radicals can affect the structures of nucleotides and disrupt base pairing during DNA replication
What is an example of a physical mutagens?
Ionising radiation
What is an example of a Chemical mutagen?
Deaminating agents
What is an example of a biological mutagen?
-Viruses
-Alkylating agents - alkyl groups are attached to bases resulting in the incorrect pairing of bases
What are the different mutations formed in chromosomes?
Deletion
Translocation
Inversion
Duplication
What is Deletion in chromosome mutation?
A section of the chromosome is lost
What is duplication in chromosome mutation?
A section of a chromosome is duplicated
What is translocation in chromosome mutation?
A section of the chromosome breaks off and joins another non-homologous chromosome
What is inversion in chromosome mutation?
A section of a chromosome breaks off, is reversed and then joins back onto the chromosome.
When does chromosome mutation occur?
Meiosis, during crossing over in Prophase I
What are the impacts of chromosome mutations?
Gametes with too few or too many chromosomes.
This can lead to developmental problems within the zygotes that survive.
What is gene regulation?
Controls what genes are switched on or off and the rate of synthesis of proteins.
What is the function of regulatory mechanisms?
Control the expression of different genes at different points in time.
This ensure that the correct gene is expressed in the correct cell at the right time.
What are the different regulatory mechanisms?
Transcriptional
Post-transcriptional
Post -translational
What is gene regulation used for in multicellular organisms?
Differentiation of cells
Cells work together in co ordination
What does the transcriptional mechanism control?
The expression of genes to control whether transcription occurs or not .
What does the post-transcriptional mechanism control?
Modifying mRNA to regulate the types of protein translated
What does the post-translational mechanism control?
Modifies proteins after synthesis which changes their function
What are the similarities in the gene expression of eukaryotes and prokaryotes?
Both respond to stimuli by changing gene expression
Both change product synthesis rates according to demand
What are the differences in the gene expression between prokaryotes and eukaryotes?
Prokaryotes
Responses produced are simple
Only respond to changes in the external environment
Eukaryotes
Responses produced are complex
Respond to changes in the internal and external environment
What is the structure of a chromatin?
DNA is wound around histone proteins forming chromatin.
The DNA is negatively charged and coils around the positively charged histone
What is Heterochromatin?
Tightly wound DNA
What is Euchromatin?
Loosely wound DNA
What are examples of epigenetics?
-Adding acetyl groups of phosphate groups to histone proteins
-Adding a methyl group to DNA
What is the effect of decondensing chromatin on transcription?
Activates transcription
What is the effect of condensing chromatin on transcription?
Suppresses transcription.
What is a structural gene?
A gene that codes for proteins in the body needed for structure and function
What is a regulatory gene?
A gene that codes for transcription factors
What are transcriptional factors?
Proteins that can bind to the DNA to inhibit or initiate transcription, so only certain parts of the DNA are expressed.
How are transcriptional factors able to bind to DNA?
The proteins have a unique 3D shape which is complementary to the sequence of bases.
Describe how the transcription of target genes are expressed in eukaryotes
Target genes can be expressed when specific transcriptional factors move from the cytoplasm into the nucleus where they bind to DNA.
This can either inhibit or initiate genes so only certain proteins are produced
During initiation, RNA polymerase is able to bind, initiating transcription so mRNA is formed for the translation of a particular protein.
During inhibition, RNA polymerase is inhibited from binding preventing transcription.
What happens when a transcriptional factor does not bind to DNA?
The gene becomes inactive so the protein will not be made
What controls transcription in eukaryotes?
Transcriptional factors
Epigenetics
What controls transcription in prokaryotes?
Operons
What is a repressor protein?
A protein that inhibits the expression of one or more genes
What is an operon?
A group of structural genes that are under the control of the same regulatory mechanism and are expressed at the same time.
What is lac operon?
Found in E.coli composed of three genes, lac Z, lac Y and lac A that aid lactose digestion.
What are the three genes in lac operon?
Lac Z
Lac Y
Lac A
What is the function of lac operon?
Regulates the transcription of the genes that aid lactose digestion to meet demands, as this is only needed when glucose is short.
What is lac I?
A regulatory gene found near the operon, which codes for a repressor protein that inhibits transcription when no lactose is present.
Describe the process of lac operon gene expression in the absence of lactose
When lactose is absent, the repressor protein is constantly produced by the regulatory gene and it binds to the operator region, which prevents RNA polymerase from binding to DNA at the promoter region so transcription is inhibited so only the enzymes used for the respiration of glucose are made.
Describe the process of lac operon gene expression in the presence of lactose
In the presence of lactose, lactose will bind to the repressor protein causing it to change shape. This change prevents the repressor protein from binding to the operator and therefore RNA polymerase can bind to the promoter region. Transcription of lac operon can then occur so lactase enzymes can be made to respire lactose.
How can the rate of transcription for lac operon be increased?
The rate of transcription needs to be up-regulated in order to produce the required quantity of enzymes to metabolise lactose efficiently. This is achieved through the binding of the Cyclic AMP receptor protein (CRP), however CRP can only bind and increase the rate of transcription once it has bound to cAMP.
What are epigenetics?
A heritable (can be passed from cell to cell during cell division) change in gene function without changing the DNA base sequence.
What are epigenetics caused by?
Changes to the environment which can inhibit transcription
What is the Methylation of DNA?
A methyl group is added to DNA and attached to a cytosine base. This makes histone proteins more hydrophobic so they bind tightly to each other causing DNA to coil tighter.
Condensing chromatin
What happens to transcription when a methyl group is added to DNA?
Transcription is inhibited as transcriptional factors are prevented from binding and instead attracts proteins that condense the DNA- histone complex.
This prevents a section of DNA from being transcribed.
What happens when acetyl groups are added to Histone proteins?
Adding acetyl groups of phosphate groups reduces the histone proteins positive charge so DNA binds loosely. Decondensing chromatin.
What happens to transcription when acetyl groups are removed from Histone proteins?
The removal of acetyl groups inhibits transcription.
This is because when acetyl groups are removed, the histone become more positive and are attracted more to the phosphate group on DNA.
The DNA and histones therefore become more strongly associated so it is harder for transcription factors to bind.
When does Euchromatin occur?
Decreased methylation
Increased acetylation of associated histone proteins
When does Heterochromatin occur?
Increased methylation of DNA
Decreased acetylation of associated histone proteins
How does the presence of glucose change the rate of transcription of the lac operon?
The presence of glucose prevents the CRP and cAMP from binding resulting in slow transcription.
What is pre mRNA?
The product of transcription before modification has taken place to produce mature mRNA.
Pre mRNA contains introns and exons.
What are introns?
Non-coding DNA
What are exons?
Coding DNA
What are the processes within post transcriptional control?
Pre mRNA can be modified as a result of:
-RNA processing
-RNA editing
Describe how pre mRNA is modified during RNA processing
Pre mRNA is modified in the nucleus
-Splicing occurs where the introns are removed and the exons are joined together
-A cap is added to the 5’ end of the mRNA and a poly-A tail (long sequence of adenine bases) is added to the 3’ end.
What is the purpose of adding caps and tails to the pre mRNA?
Helps to stabilise mRNA and delay degradation within the cytoplasm
Describe how mRNA can be modified as a result of RNA editing?
The mRNA nucleotide can also be changed as a result of base insertion, deletion or substitution
This increases the number of proteins that can be produced from a single mRNA
What are protein kinases?
Enzymes which catalyse the addition of phosphate groups to proteins.
The addition of the phosphate group changes the tertiary structure and function of the protein activating it.
What is the role of post translational control?
Modifying proteins that have already been synthesised.
Describe the processes that can occur during post translational control
-Non protein molecules can be added- lipid or carbohydrate chains
-modifying amino acids and the formation of bonds
-modification as a result of cAMP
-folding or shortening of proteins
What is a body plan?
The general structure of an organism
What is the homeodomain?
Part of a protein that acts as a transcriptional factor by binding to DNA at the beginning of developmental genes to activate or repress transcription.
Describe the process of apoptosis
Enzymes break down cell components and DNA
The cell shrinks and breaks into fragments
Phagocytes then engulf and digest the fragments
What are Homeobox genes?
Sequences of genes which code for homeodomain proteins that regulate the expression of other genes that are involved in the formation of the body in the early stages of development as an embryo.
Homeobox genes are highly conserved (change very little)
What organisms contain homeobox genes?
Plant, animals and fungi have homeobox genes to control the development of their bodies
What are Hox genes?
Type of homeobox gene found in animals that is responsible for the correct body development and positioning of body parts (body plan)
The order of the Hox genes in the DNA is the order which their effects are expressed on the organism
What is the role of mitosis in the development of body forms?
Results in an increase in the number of cells, leading to growth
What is the role of apoptosis in the development of body forms?
Programmed cell death- removes unwanted cells
How can the Hox genes that regulate mitosis and apoptosis be impacted?
The genes that regulate apoptosis and the cell cycle can be impacted by external (temperature) and internal (hormones and stress) stimuli.
The effect of this is highest during growth and development.
Why does the cell cycle need regulating by genes?
Ensure new cells are only made when they are needed for growth and repair
-to preserve energy
-prevent tumour formation.
What is the role of the tumour suppressor gene?
Responsible for making proteins that stop the cell cycle from continuing
What is the role of proto-oncogenes?
Responsible for producing proteins that initiate the cell cycle.
