Topic 2: Genes and Health Part 2 Flashcards
what is exocytosis
the release of substances, usually proteins/polysaccharides. from the cell as vesicles (small membrane bound sacs) fuse with the cell membrane, the substance can thenn diffuse out
what is endocytosis
when substances are taken into a cell by the creation of a vesicle from the cell membrane
part of the cell membrane engulfs the solid/liquid material to be transported
what are enzymes
- globular proteins that act as biological catalysts
- speed up reactions within cells that would otherwise occur very slowly
- have an active site with a specific shape
- intracellular/extracellular
how is the active site of an enzyme made to be specific
the primary structure (initial sequence of amino acids) determines the enzymes tertiary structure which determines the shape
a change in a gene determining the primary structure could change the tertiary structure of the enzyme produced and therefore the specificity
what is the Induced Fit Model for enzymes
rather than only the shape of the substrate being specific to the active site, it has to be able to make the active site also change shape so it can lock the substrate more tightly in shape
how do enzymes lower activation energy - the actual method
- if two substrate enzymes have to be joined to form the product, attaching them both to the enzyme can hold them closer together and reduce repulsion so that they bond more easily
- if they enzyme is catalysing a breakdown reaction, fitting into the active site will put more strain on bonds in the substrate so that it breaks up more easily
how do charges affect enzyme-substrate complexes
many of the amino acids making up the enzyme have positively and negatively charged chemical groups
for the substrate to fit in the active site, electrical charges on the substrate molecule and the enzyme should be opposite so that they attract
what factors affect enzyme catalyzed reactions
inhibitors (non + competitive)
enzyme concentration
substrate concentration
temperature
pH
how does a competitive inhibitor work
it blocks the substrate from binding to the active site by binding in it’s place
how does a non-competitive inhibitor work
it allows the substrate to bind to the active site but blocks the reaction from taking place
how does temperature affect enzyme catalyzed reactions
a soluble protein denatures and becomes insoluble as well as getting inactivated
an insoluble fibrous protein will lose it’s structural strength
why does a pH change affect enzyme catalysed reactions
pH change causes bonds maintaining the tertiary structure of the active site to break, causing the shape to distort
the charge on some amino acids making up the active site are also altered, so the substrate can’t be held in there the same way
how does substrate concentration affect enzyme catalyzed reaction
it increases the rate of reaction until a saturation point is reached
how does enzyme concentration affect enzyme catalyzed reaction
it increases the rate of reaction until substrate concentration becomes the limiting factor
where in a cell is DNA stored
it’s stored in almost every cell, in the nucleus
if a cell doesn’t have a nucleus then it is stored in the cytoplasm
what are the components of a nucleotide
1 phosphate group
1 nitrogen-containing organic base
1 pentose sugar molecule (deoxyribose in DNA vs ribose in RNA)
all of which are linked by condensation reactions
which are the purine bases
adenine and guanine; they have a double ring structure
what are the pyrimidine bases
thymine, cytosine, uracil
what bases are used DNA
adenine, cytosine, guanine, thymine
what bases are used in RNA
adenine, guanine, cytosine, uracil
how is DNA, a polynucleotide formed
phosphodiester bonds form between mononucleotides through condensation reactions, between the sugar of one nucleotide and the phosphate group of another
two antiparallel polynucleotides are twisted together
describe transcription
in nucleus
- the enzyme RNA polymerase attaches to the DNA, at a start codon in front of a gene in a non coding region
- RNA polymerase separates the two DNA strands by breaking hydrogen bonds, the DNA molecule unwinds
- the RNA polymerase enzyme moves along one of the separate strands, the antisense strand, adding complementary RNA nucleotides (U instead of T)
- nucleotides link by phosphodiester bonds to form a strand of messenger RNA, mRNA
- when RNA polymerase reaches a stop codon, it stops making mRNA and detaches from the DNA
- the hydrogen bonds between the unwound DNA strands re-form, the DNA molecule ‘zips up’
- mRNA travels out of the nucleus via the nuclear pores to attach to a ribosome
what two words are used to describe the DNA code + what do they mean
degenerate - more than one triplet can code for the same amino acid
non-overlapping - each triplet is separate and bases aren’t shared
what is a gene
the sequence of bases on a DNA molecule that codes for the sequence of amino acids in a polypeptide chain
describe translation
- the mRNA carrying the genetic code leaves the nucleus and attaches to the ribosome in the cytoplasm, so the protein can be assembled
- the ribosome reads and moves along the mRNA strand a codon at a time
- a tRNA molecule brings the specific amino acid to the MRNA in the order of the codons
- as the ribosome moves along the mRNA hydrogen bonds form between the codon and anticodon (anticodon is part of tRNA structure which is complementary to the codons) of mRNA and tRNA
- peptide bonds form between the amino acids, forming a protein
- the process continues until a stop codon is reached on the mRNA, the polypeptide chain stops growing and detaches from the ribosome (bc tRNA doesn’t have an anticodon for a stop codon)
what comes first in protein synthesis, translation or transcription?
transcription, then translation
what is a start codon
AUG
what is a stop codon
a codon that has no tRNAs with complementary anticodons to these sequences, meaning no amino acid can be transferred
genes, chromosomes and DNA relativity
DNA makes up genes which are carried in chromosomes which are kept in cells
outline DNA replication
it has to occur before mitosis
- replication begins at a specific sequence on the DNA molecule
- DNA helicase unwinds and unzips the DNA, by breaking hydrogen bonds joining base pairs and forming to separate strands
- the new DNA is built up from ACGT that are abundant in the nucleoplasm; they attach to their complementary bases on the old strand
- DNA polymerase joins the new nucleotides to each other with phosphodiester bonds which forms the phosphate-sugar backbone
- a winding enzyme winds up the new strands to form double helices
- the two new molecules are identical to the old one
what is the name of the accepted model for DNA replication
semi-conservative replication, a theory put forward by meselsohn and stahl
how was the semi-conservative replication of DNA proven?
bacteria was grown in the broth of a heavy isotope of nitrogen, N15 (because all DNA bases contain nitrogen)
the DNA and it’s solution was centrifuged to see where the DNA strand would lie, it was low in the tube because it was heavy
The next generation was grown in an N14 broth and the same process was done but the DNA was now in the middle because the DNA was a hybrid between N14 and N15
it means that there is genetic continuity between generations
define genotype
the genetic makeup of an organism
what is incomplete dominance
the heterozygous genotype produces a phenotype that falls in-between that expected by the dominant and recessive (eg white is dominant and red is recessive, so it ends up pink)
outline the experiment using catalase that looks at rate of product formation
- add a set volume and conc of hydrogen peroxide to a boiling tube with a suitable buffer solution to keep pH constant
- set up with a bung in the tube and a delivery tube going into an upside down measuring cylinder in a trough of water
- add a set volume of one of the catalase concs into the boiling tube and quickly replace the bung
- record volume of oxygen produced every 30 seconds for 5 minutes, measured in cm^2 and with a stopwatch
- repeat twice and then calculate mean for every 30 second interval
- plot data on graph with oxygen volume produced against time and determine initial rate using a tangent
- repeat the entire experiment with all other catalase concentrations
outline the experiment that measures the rate of the removal of the substrate
- set up a colorimeter with a red filter and zero it using a cuvette containing iodine dissolved in potassium iodide solution (browny-orange)
- in another cuvette, pipette a set volume of one of the starch conc and a set volume of iodine dissolved in potassium iodide solution and mix which will turn the solution a dark blue-black. place cuvette in zeroed colorimeter and record percentage absorbance
- add a set volume and conc of amylase to the cuvette and start a stopwatch immediately
- every 10 seconds for 5 minutes, record absorbance on colorimeter
- repeat twice and then calculate mean absorbance for every 10 second interval
- plot absorbance (arbitrary units^-1) against time and draw a tangent to estimate initial rate of reaction
- repeat everything for other starch concentrations
how many hydrogen bonds form between A and T
two
how many hydrogen bonds form between C and G
three
c and g rhyme with 3
what is mRNA
its made in the nucleus during transcription
three adjacent bases is a codon
it carried genetic code from DNA in nucleus to the cytoplasm where its used during translation to make a protein
what is tRNA
it’s found in the cytoplasm
each tRNA carries a specific amino acid at one end and a sequence of three bases at the other end, called an anticodon which recognises codons on the mRNA
it carries amino acids used to make proteins to the ribosomes during translation
define allele
alleles are different versions of the same gene found at the same locus on a chromosome
what happens if a base is missing in a base sequence
the bases will move back one, causing the entire chain after that point to shift
how can CF be tested for
- CF causes a higher salt concentration in sweat, so this is tested for
- there are higher levels of the protein trypsinogen in the blood of people with CF, it is tested for in all UK babies
how is genetic screening used and for what
it identifies the presence of abnormal genes/alleles in the DNA of cells
it’s done to confirm a diagnosis, identify carriers and test embryos
what are the two opportunities to take a sample for genetic screening
whilst in the womb or once born
how can you take a sample whilst in the womb
remove a single cell
remove some fluid or blood (contains cells)
cut out a piece of tissue
drawblood from the umbilical cord
how do you take a sample once born
use hair/ heel prick test (collects blood) / swab inside of cheek
what are the 4 different types of genetic screening
- non-invasive prenatal diagnosis (NIPD)
- amniocentesis
- chorionic villus sampling (CVS)
- preimplantation genetic diagnosis (PGD)
outline and evaluate preimplantation genetic diagnosis (PGD)
done with IVF, cell samples are taken from the embryo and analysed before implanting it
+ reduces chance of having a baby with a genetic disorder
+ avoids issues around abortion
– it could lead to designer babies in the future
– false results
define pre-natal test
tests that occur once the embryo is developing inside the uterus
outline and evaluate amniocentesis
it is usually carried out at 15-20 weeks of pregnancy
a fine needle obtains an amniotic fluid sample through the abdomen which contains foetal cells, these contain DNA that can be analysed
– 1% chance of miscarriage
– chance of bacterial infection
+ lower chance of miscarriage than CVS
+ there is a rapid test that only tests for a few, common disorders and takes 3-4 days
outline and evaluate chorionic villus sampling (CVS)
11-14 weeks along
fine needle moves some cells from the placenta (chorionic villi)
- 1-2% miscarriage chance
- chance of causing infection when taking the sample
- abortion can be encouraged if tests are positive
+ can be done earlier than amniocentesis, making it less traumatic physically
outline non-invasive prenatal diagnosis (NIPD)
a new and rapidly developing procedure
DNA fragments in the mother’s blood during pregnancy are analysed
it can be detected at 4-5 weeks but there’s only enough to analyse at 7-8 weeks
only limited conditions can be screened for (currently)
how is mRNA synthesised at a DNA template strand
RNA nucleotides align with complementary bases on DNA
RNA nucleotides joined together by RNA polymerase forming phosphodiester bonds
what information does DNA store
genetic information
what information does RNA contain
information about protein synthesis as one of its main functions is transferring genetic info from the DNA to ribosomes
how do mononucleotides form DNA
condensation reactions occur between the phosphate of one mononucleotide and the sugar group of another
ester bonds
briefy outline the structure of DNA
a polymer made of two antiparallel (running in opposite directions) polynucleotide strands, twisted to form the DNA double-helix
outline the types of RNA
mRNA
- made in nucleus during transcription
- three adjacent bases is a codon
- carries genetic code from DNA in nucleus to the cytoplasm where it’s used in translation to make a protein
tRNA
- found in cytoplasm
- amino binding site at one end and anticodon at other end (3 base sequence)
- carries amino acids for proteins to the ribosomes during translation
what is the part of DNA with a pentose sugar and phosphate group bound together known as
sugar-phosphate backbone
what bonds are found in DNA
between nitrogenous bases: H bonds
between pentose sugar and nitrogenous base: glycosidic bonds
between phosphate group and pentose sugar: phosphodiester bonds
what are features of dna
triplet code
non-overlapping
degenerate
what is the best way to study enzymes and allow for fair comparison between conditions
look at initial rate
explain how optimal temp affects rate of enzyme catalysed reaction
more kinetic energy
more frequent collisions between the enzymes and substrates
more enzyme-substrate complexes formed
what is a recessive allele
a faulty version of the gene
what do you bring up when talking about things that will stop mRNA
they’ll bind to either mRNA or ribosome, changing the shape and preventing the two from binding
translation can therefore not occur
tRNA then can’t bind to mRNA and so, the polypeptide isn’t synthesised
what is the name of the centre of a chromosome and what is the name of where spindle fibres come from
centre: centromere
spindle: centrioles
what is a centriole vs centromere
centromere: centre of chromosome
centriole: spindle fibres
