Chapter 19 Genetics of Living systems

define mutation

a change in the nucleotide base sequence of DNA

define substitution mutation

one base in the codon has changed

define insertion mutation

nucleotide is added to the base sequence of DNA

define deletion mutation

nucleotide is removed from the base sequence of DNA

define silent mutation

there is no effect on the phenotype of an organism because normally functioning proteins are still synthesised

define missense mutation

the incorporation of an incorrect amino acid into the primary structure when the protein synthesised

results in a protein that could have a silent, beneficial, or damaging mutation

define conservative mutation

the amino acid change leads to an amino acid being coded for which has similar properties to the original meaning the effect of the mutation is less severe

define nonsense mutation

results in a codon becoming a stop codon resulting in a shortened protein synthesised which is normally non-functional

define damaging mutation

the phenotype of an organism is affected in a negative way because proteins are no longer synthesised/ proteins synthesised are non-functional

define beneficial mutation

the phenotype of an organism is affected in a positive way because proteins synthesised results in a useful characteristic

define frameshift mutation

the insertion or deletion of nucleotide bases in numbers that are not multiples of three

define point mutation

only one nucleotide is affected

define mutagens

chemical, physical, or biological agents that increase the rate of mutation

describe an example of physical mutagens

ionising radiation

break one or both DNA strands

describe an example of chemical mutagens

deaminating agents

chemically alter bases in DNA which changes the base sequence

give examples of biological agents

alkylating agents = methyl/ethyl groups are attached to bases resulting in the incorrect pairing of bases during replication

base analogs = incorporated into DNA in place of the usual base during replication, changing the base sequence

viruses = viral DNA may insert itself into a genome, changing the base sequence

define amorph

mutation that results in the loss of function of a protein

define hypomorph

mutation that results in a reduction of function of a protein

define hypermorph

mutation that results in a gain of function of a protein

define chromosome mutations

mutations that affect the whole chromosome/ a number of organisms within a cell

normally occur during meiosis

4 ways the structure of a chromosome can be changed

deletion = a section of chromosome breaks off and is lost within the cell

duplication = sections get duplicated on a chromosome

translocation = a section of a chromosome breaks off and joins another non-homologous chromosome

inversion = a section of chromosome breaks off, is reversed, and joins back onto the chromosome

define housekeeping genes

genes that code for enzymes which are necessary in reactions present in metabolic pathways that are constantly required (e.g. respiration)

define tissue-specific genes

genes that code for protein-based hormones that are only required at certain times to carry out a short-lived response

4 mechanisms in which genes are regulated

transcriptional = genes turned on/off

post-transcriptional = mRNA modified = regulates types of proteins produced

translational = translation stopped/started

post-transcriptional = proteins modified after synthesis which changes their functions

state mechanisms of transcriptional control

chromatin remodelling

histone modification

lac operon

define heterochromatin

tightly wound DNA causing chromosomes to be visible cell division

transcription of genes not possible because RNA polymerase cannot access the genes

define euchromatin

loosely wound DNA present during interphase

transcription of genes possible

describe histone modification

DNA (negatively charged) coils around histones (positively charged)

the addition of acetyl groups/ phosphate groups reduces the positive charge on the histones causing DNA is coil less tightly = allowing certain genes to be transcribed

the addition of methyl groups makes the histones more hydrophobic so they bind more tightly to each other causing DNA to coil more tightly = prevent transcription of genes

define epigenetics

the control of gene expression by the modification of DNA

steps of transcription of structural genes on the lac operon

1) when glucose conc is high, there is no need to digest lactose

2) a regulatory gene (LacI) is transcribed and mRNA is translated = produce repressor protein

3) repressor binds to operator = blocks promoter region

4) RNA polymerase cannot bind to promoter = no transcription of structural genes (LacZ, LacY, LacA)

5) limited glucose, lactose binds to repressor and acts as an inducer

6) this changes the shape of the repressor = cannot bind to operator

7) promoter exposed = RNA polymerase binds = transcription of 3 structural genes which produces enzymes which convert lactose = glucose + galactose

role of cAMP

the binding of cAMP+CRP complex increases the rate of transcription when RNA polymerase binds to the gene to produce the required quantity of enzymes needed to metabolise lactose efficiently

state mechanisms of post transcriptional control

splicing

RNA processing

RNA editing

describe RNA processing

1) a cap (modified nucleotide) is added to the 5’ end

2) a tail (long chain of adenine nucleotides) is added to the 3’ end

3) these help stabilise mRNA and delay degradation in the cytoplasm

4) splicing also occurs

define splicing

RNA is cut at specific points so that introns (non-coding DNA) are removed and exons (coding DNA) are joined together

define RNA editing

nucleotides are added, deleted, or substituted in the mRNA base sequence

makes proteins of different functions

state mechanisms of translational control

degradation of mRNA = mRNA is broken down so that protein is not made

binding of inhibitory proteins to mRNA prevents it binding to ribosomes = prevents synthesis of proteins

activation of initiation factor which help the binding of mRNA to ribosomes (by phosphorylation using protein kinases)

define protein kinase

enzymes that catalyse the addition of phosphate groups to proteins = changes the tertiary structure/function of a protein

state mechanisms of post-translational control

addition of non-protein groups

modifying amino acids and the formation of disulphide bridges

folding/shortening of proteins

modification by cAMP = in lac operon cAMP increases transcription rate

define morphogenesis

the regulation of the pattern of anatomical development

define body plan

the sum of organisation and combination of an organism’s body parts and features

define homeobox genes

a group of regulatory genes which all contain a homeobox and control the morphogenesis (body development) of unicellular organisms

are highly conserved

define hox genes

a group of homeobox genes that are only present in animals which are responsible for the correct positioning of body parts

define homeodomain

part of a protein which binds to DNA and switches other genes on and off

define radial symmetry

an organism can be divided into similar halves by any plane from the central axis (e.g. in starfish)

define bilateral symmetry

organism has both left and right sides and a head and tail

why are homeobox genes highly conserved

any mutations in the body plan will not be passed on because the organism will not be able to survive

describe the role of mitosis and apoptosis in the proliferation of multicellular organisms

mitosis leads to an increase in cell number as the embryo develops and grows

apoptosis removes unwanted cells and tissues