Molecules Revision Q's Flashcards
Define the human genome (1)
The human genome is a human’s complete genetic material. 1.5% of the genome codes proteins, whereas the rest is interons, regulatory sequences, etc.
What is the difference between a gene and an allele?
A gene is a section of DNA that codes for a single protein or polypeptide and is the unit of heredity.
An allele is one of two or more alternative forms of a gene at corresponding sites (loci) on homologous chromosomes, which determine alternatice acharacters of inheritence.
What is the difference between a genotype and a phenotype?
A genotype is the genetic information carried by a pair of alleles.
A phenotype is the physical/observable manifestation of the genotype.
Cru di chat is a genetic condition which is characterised by a high pitched cry and is caused by deletion of 5p15.2. What does this nomenclature indicate?
5p15.2 indicates the loci is situated on chromosome 5, the short arm, band 15, position 2.
What is the central dogma?
That DNA replicates and is then transcribed forming messenger RNA. mRNA is then translated into sequences of amino acids to form the polypeptide or protein. The outcome is gene expression.
Describe the main process involved in protein synthesis from DNA (4).
1) DNA is unzipped
2) One strand of DNA is then transcribed into mRNA in the nucleus in the 5’-3’ direction. This mRNA then migrates to the cytosol through the nuclear pores.
3) The mRNA then binds to ribosomes and tRNA bring the required amino acid to the binding site. The tRNA has the anticodon.
4) The peptide link between adjacent amino acids is made. Translocation then occurs as the mRNA is shifted along one codon into the p-site, making the a-site availible.
5) When completed, the polypeptide undergoes post-translation modification in the RER and is delivered by the Golgi apparatus.
What is the difference between a membrane channel and a membrane carrier?
A membrane channel facilitates diffusion of a substance down a concentration gradient. Passage is quick, but less specific. Regulation is by opening and closing of the channel.
A membrane carrier catalyses the passage of a substance across a membrane and does this by physically binding the substance and moving it across the membrane. This process is slower but more specific.
What is the difference between facilitated and simple diffusion?
Facilitated diffusion is when a transporter is used to transport a substance down the concentration gradient.
Simple diffusion is when a substance diffuses down the concentration gradient across the bi-lipid cell membrane without help from a transporter.
Describe the three classes of active transporters, giving an example of each.
V-type: transport substances into vesicles to create an acidic environment. They are not phosphorylated (eg. vacuolar ATPase).
P-type: normally on the plasma membrane they transport by forming a phosphotransporter intermediate. Phosphate is transferred from ATP to an aspartate residue and then hydrolysis of this drives transport (eg. Na+:K+ pump/Calcium pump/Proton pump (H+:K+)).
F-type: uses the concentration gradient to drive ATP synthesis (eg. mitochondrial ATP synthase -H+ gradient generated by oxidative phosphorylation and is then stored synthesise ATP).
Describe how glucose is taken up into the epithelium of the intestines and then released into the blood stream. How is glucose then transported into an erythrocyte from the blood stream of the intestines?
1) Na+:K+ -ATPase pumps Na+ out of the cell via active transport against the concentration gradient.
2) A Na+:glucose symporter uses the Na+ gradient to drive glucose into the cell.
3) A glucose channel (GLUT2) on the blood/epithelium membrane of the cells allows facilitated diffusion of glucose down the concentration gradient into the cell.
4) A GLUT1 transporter on the erythrocyte membrane allows facilitated diffusion ie. down the conc gradient into the cell.
5) Conc gradient is maintained by glucose being converted into glucose-6-phosphate in the cell, thus the concentration outside the cell remains higher.
What are the ion concentrations inside and outside of a typical cell for K+, Na+, Ca2+, Cl- and organic molecules?
K+: inside = 160mM; outside = 5mM Na+: inside = 10mM; outside = 150mM Ca2+: inside = 0.2µM; outside = 2mM Cl-: inside = 5mM; outside = 115mM Organic molecules: inside = 165mM; outside = 40mM
Define the term symporter and antiporter and give an example of each in the human body.
A symporter is a co-transporter that carries two substances across a cell membrane in the same direction. Eg. Na+:glucose symporter in the small intestine, which uses the motive force of the flow of Na+ into the cell to drive glucose in against its conc gradient.
An antiporter is a carrier that carries two substances across a cell membrane in opposite directions. Eg. H+:Na+ antiporter where Na+ flows in and H+ out.
