Topic 2 Flashcards
in genetic screening, why do carriers sometimes show a false positive
the recessive allele may be detected
what does implantation diagnosis consist of
embryos are created through IVF are tested to see if they carry faulty allele. Only the healthy embryos will be implanted
however the process is expensive and unreliable
define allele
a version of a gene
define a recessive allele
an allee which isn’t expressed when a dominant allele is present
define dominant allele
an allele is always expressed
define incomplete dominance
neither allele is dominant over the other and the resultant phenotype is a mix
what symptoms can cystic fibrosis present in gas exchange
mucus can block bronchioles which leads to less O2 to the alveoli so smaller concentration gradients
thin layer of mucus can make it difficult for O2 and CO2 to diffuse
what symptoms can cystic fibrosis present in reproduction
in men - sperm duct blocked with mucus so sperm can’t leave the testes
in women - mucus blocks the cervix so sperm cannot reach the egg
what symptoms can CF present in digestion
blocks the pancreatic duct so digestive enzymes cannot reach the digestive system so food isn’t properly digestive and nutrients aren’t absorbed so there is difficulty gaining weight
enzymes trapped in the pancreas cause fibrosed cysts and damage insulin producing cells which can also lead to diabetes
what does amniocentesis consist of
a syringe with a needle is inserted into the amniotic sac and fluid is extracted and foetal cells are then separated. This is cultured for 2-3 weeks
DNA is karyotyped, biochemical tests are also carried out on both the fluid and cells
this is when the foetus is 14-16 weeks
what does chorionic villus sampling consist of
a syringe is inserted in the vagina to take a sample of embryonic tissue from the placenta (the chorionic villus).
DNA is karyotyped when the fetus is 8-10 weeks old
why do people with CF have sticky mucus
the CFTR channel protein is non-functional therefore the Na+ channel (ENac) is always open so Na+ ions move into the cell and to the tissue fluid on the basal membrane
this causes the Cl- to move down the concentration gradient, water goes out from the mucus and into the cell and tissue fluid
what are the factors that one must consider in relation to prenatal screening
risk of miscarriage, potential abortion, religious beliefs of right to life, cost of healthcare, risks/consequences of false positives/negatives
what is meant by monohybrid inheritance
inheritance of 1 characteristic
when can mutations occur
DNA replication, transcription and translation
how do bodies decrease the viscosity of mucus on the apical membrane
Cl- is pumped into the cell across basal membrane
Cl- diffuses through open CFTR channels to outside apical membrane
Na+ diffuses down electrical gradient in mucus
Elevated salt concentration in the mucus draws water out of the cell and into the mucus via osmosis
what did Meselon and Stahl’s experiment consist of
- E coli bacteria cultured in 15-N containing medium
- transferred into a 14-N containing medium
- DNA extracted after each generation and centrifuged into BaCl solution
the heavier the DNA was, the deeper it sank in the test tube
how did Meselon and Stahl’s experiment disproved the other theories
- In a conservative model, super heavy DNA would be expected with a newly lighter DNA as generations passed - 1 of each
- In dispersive, only 1 layer of equally dense DNA would be seen getting lighter and lighter - a mix of heavy and light
- Results showed intermediate strands of 1/2 heavy and 1/2 light after 1 generation which disproved conservative
After 2 generations, 2 layers were shown, 1 intermediate and 1 light which disproved fragmentary
semi conservative was 1 strand of intermediate and 1 strand of light in a double helix
why isn’t heat used to accelerate reactions in organisms rather than enzymes
heat would damage cell tissues
how do enzyme concentration affect the reaction rates
as the enzyme concentration increases, the rate increases as there is a higher chance of successful collisions therefore more enzyme-substrate complexes formed per unit of time so more products are released
in experiments how could
temperature be controlled
pH be controlled
using a water bath with the temperature as close to optimum as possible
using a buffer solution as close to optimum
what happens during semi-conservative replication of DNA
- DNA helicase breaks the hydrogen bonds between bases to unzip DNA
- DNA nucleotides align with their complementary bases and DNA polymerase creates phosphodiester bonds that join nucleotides together
- DNA ligase joins the partly formed strands together
- 2 identical daughter strands are created - 1 old and 1 new
what did the conservative DNA replication model mean
1 whole completely new double helix is synthesised
what did the dispersive/fragmentary DNA replication model mean
the new DNA molecule was created as a mix of old and new parts
what does the induced fit hypothesis state
enzyme changes shape to fit substrate when substrate is near while lock and key model theorizes that the enzyme and substrate are always complementary in shape and the enzyme doesn’t change shape
what are enzymes
biological catalysts
how do enzymes accelerate rates of reaction
Lower activation energy by providing a lower energy pathway, a more favourable pH in the active site
using charge to put strain in bonds to break them
bring reactants together by using charge so that bonds form more easily
what types of proteins are enzymes
globular
what are intracellular enzymes
enzymes that work inside the cell
e.g. DNA polymerase
what are extracellular enzymes
enzymes that work outside the cell
e.g. digestive enzymes
Explain Lock and Key Theory
- Random movement causes enzyme and substrate to collide and the substrate enters the active site.
- Enzyme-substrate complex forms = shared groups attract, distort the substrate and aid in bond breaking/formation
- Products are released from active site, leaving it undamaged and ready to accept a new substrate
what does structure of a protein determine
its function
what type of protein is haemoglobin
globular
what type of protein is collagen
fibrous
describe structure of haemoglobin
globular with 4 polypeptide chains -2 alpha and 2 beta - each containing a haem prosthetic group
what 2 types of secondary structure are there
alpha helix or beta pleated sheet
describe the structure of collagen
fibrous with 3 polypeptides - 2 alpha and 1 beta
how is a tertiary structure of a protein created
alpha helix / beta pleated sheet fold further and create a new structure held together by disulphide bridges and ionic bonds between R groups
how is the quaternary structure of a protein created
folded polypeptides joined by hydrogen bonds - disulphide bridges and ionic binds between R groups
what is the general formula for an amino acid
a central carbon, a hydrogen, an amine group (NH2) and a carboxylic acid (COOH)
how are peptide bonds created
the OH in the carboxyl joins the H in another amino acid in a condensation reaction to remove water and form peptide bonds
what is the primary structure of a protein
sequence of amino acids
how does secondary structure of a protein formed
amino and carboxyl groups carry small amounts of charge
charge is negative on the CO and positive on the NH
result in H bonds forming between parts of the chain to stabilize the structure - alpha helix and beta pleated sheet
describe the role of tRNA in the production of protein part of a glycoprotein
each tRNA brings a specific amino acid to the ribosome
the tRNA with the complementary anticodon binds to mRNA codon
tRNA bonds to ribosome
compare and contrast the process of transcription with the process of DNA replication
Similarities:
involve formation of a polynucleotide
involve DNA helicase
Differences:
transcription uses RNA nucleotides whereas replication uses DNA nucelotides
transcription uses RNA polymerase whereas replication uses DNA polymerase
transcription produces a single strand of mRNA/only copies template strand of DNA whereas replication produces double stranded DNA/ copies both strands of DNA
explain how change of 1 amino acid could lead to a change in the structure and properties of haemoglobin protein
different sequence of amino acids/primary structure
a different amino acid will have a different R group therefore secondary/tertiary/quaternary structure will change due to a change in a hydrogen bond holding the molecule in its 3D shape
haemoglobin may not bond to oxygen
describe the role of tRNA in the production of leptin
tRNA molecules transport amino acids to the ribosome
tRNA molecules has an anticodon that bonds to/recognises a codon on each mRNA
each tRNA carries a particular amino acid
describe how the primary structure of a protein allows it to be soluble
primary structure/ sequence of amino acids determines the folding of polypeptides
forming globular structure
hydrophobic R groups located in the centre of the protein/ hydrophilic r groups on the outside
water forms hydrogen bonds with protein/ hydrophilic groups
describe how a frameshift mutation could result in the production of leptin with a variety of shorter primary structures
adding/removing one or 2 nucleotides changes the triplet code
introducing a new stop/start codon
coding for a shorter sequence of amino acids
describe how mRNA is synthesised at a template strand of DNA
RNA nucleotides align with complementary bases on DNA
RNA nucleotides joined together by RNA polymerase
describe the differences between DNA and RNA
DNA:
double stranded
contains deoxyribose sugar
contains thymine as a group
RNA:
single stranded
ribose sugar
contains uracil as a group
explain why deletion and substitution have different effects on protein structure
deletion could affect every codon on the mRNA/ substitution will only affect 1 codon
deletion is more likely to affect the position of a stop/start codon
deletion results in a different sequence of amino acids/ substitution may not affect sequence of amino acids
substitution may code for same amino acid
due to degenerate nature of genetic code
explain why antibiotics that bind to ribosomes could affect the production of proteins in bacteria
ribosome shape is altered
mRNA is prevented from binding to the ribosome/causing change in the tRNA binding
therefore translation cannot occur
protein/polypeptide isn’t synthesised
why might ribosome-binding antibiotics be used to treat bacteria that are resistant to other antibiotics
bacteria have not been exposed to new antibiotics before/ bacteria don’t have mechanisms to make them resistant to other new antibiotics
bacteria have developed resistance to other antibiotics by evolving
therefore there has been no advantage to possessing a mutation to bypass the new antibiotic
describe the role of the CFTR protein in ensuring that the mucus produced in the lungs has the right consistency
Cl- ions leave the cells
Na+ ions leave the cells
increasing the solute concentration
water moves out of the cell and into mucus by osmosis
describe the roles of transcription and translation in the synthesis of a globular protein by a muscle cell
the gene/ sequence of DNA for the globular proteins is transcribed
complementary base pairing between RNA nucleotides and DNA
mRNA leaves the nucleus and attaches to a ribosome
pairing between codons on mRNA and anticodons on tRNA
tRNA provides specific amino acids
the sequence of bases/codons determines the sequence of amino acid/ primary structure of the protein
compare and contrast the structure of ATP and a DNA nucleotide
Both:
contain phosphate, pentose sugar and a base
Differences:
a DNA nucleotide contains deoxyribose whereas ATP contains ribose
a DNA nucleotide could contain other bases whereas ATP only contains ATP
a DNA nucleotide contains 1 phosphate whereas ATP contains 3 phosphates/ is a triphosphate
explain the importance of primary structure functioning of ATPase
primary structure determines interaction between amino acids/ R groups
primary structure determines folding/ tertiary structure
therefore affecting shape of active site which would be complementary to ATP
Factor VIII is involved in blood clotting
Explain how a change in the primary structure of VIII could cause difficulties with blood clotting
a different primary structure results in a different sequence of amino acids
change in R group changes folding/ bonding/ secondary structure/ tertiary structure
changing shape/charge of the active site prevents a substrate from being able to bind
stopping/reducing production of fibrin
why are enzymes described as biological catalysts
they lower the activation energy and speed up the rate of biological reactions
describe what happens to proteins following translation until release form cell
proteins folded in the rough endoplasmic reticulum
proteins packaged and transported in vesicles
proteins then modified in the Golgi apparatus
leave via exocytosis
explain why enzymes that are incorrectly folded cannot carry out their function
the tertiary structure/ 3D shape would be different
therefore the active site of the enzyme would not fit/bind with the substrate/ would not be able to form an enzyme-substrate complex
therefore unable to catalyse reactions
describe how an enzyme could break down the polysaccharide components
hydrolysis of glycosidic bonds
compare and contrast molecular structure of globular and fibrous proteins
Both:
chains of amino acids
contain H bonds holding their 3D structures
Differences:
Globular have hydrophilic groups on the outside whereas Fibrous have hydrophobic groups on the outside
Globular have lots of tertiary structure and fibrous have little/no tertiary structure
describe how the structure of phospholipase allows it to hydrolyse phospholipids
different sequence of amino acids
a different R group
secondary/ tertiary/ quaternary structure will change
due to a hydrogen bond changing
haemoglobin may not bind to oxygen
give 2 differences between endocytosis and exocytosis
exocytosis - involves molecules/substances leaving the cells, involves vesicles fusing with cell surface membrane
endocytosis - involves molecules/substances entering the cells, involves formation of vesicles
explain why betalain molecules cannot move through intact cell membrane
too large to move through the cell membrane
there are no carrier/channel proteins for betalains to move through
they’re also polar and are repelled by the hydrophobic fatty acid tails/ cannot move through fatty acid tails
hydrolysis
breaking a chemical bond between 2 molecules involving a water molecule
fibrous proteins
long chain proteins that are insoluble and usually have structural roles
have hydrophobic r groups on the outside have little tertiary structure
condensation reaction
a type of reaction that bonds 2 molecules together with the removal of water and the formation of a chemical bond
dipeptide
a molecule formed by the condensation of 2 amino acids
primary structure
sequence of amino acids
secondary structure
formation of alpha helixes or beta pleated sheets
tertiary structure
the way a protein folds into a 3D structure
hydrogen bond
a weak bond formed between a slightly positive hydrogen and a slightly negative oxygen/other atom
what is haemoglobin
an example of a globular protein
used to transport oxygen
made up of 4 polypeptide chains each containing a haem group
collagen
example of a fibrous protein, provides strength to many different cell types and make up connective tissues
what is an intracellular enzyme
enzyme that works within the cell
what is an extracellular enzyme
an enzyme that works outside of the cell
what is ribosomal RNA
RNA that makes up ribosome
what is a ribosome
an organelle found in the cytoplasm that carries out protein synthesis
what is the function of an R group
a side chain that is attached to a molecule that determines chemical properties
what is the importance of hydrogen bonds
affects how many bonds form and where, will affect secondary and tertiary structure
what is the importance of hydrophobic and hydrophilic amino acid side group chains
hydrophilic = soluble in water, can affect water potential when dissolved in blood plasma
hydrophobic = insoluble in water, has no water effect
how do ionic bonds form
between oppositely charged side chains on different amino acids
what are peptide bonds
the bonds that are formed between amino acids
what is the structure of a phospholipid
1x glycerol
2x fatty acids
1x phosphate group
which part of a phospholipid is hydrohpilic and which is hydrophobic
head = hydrophilic - interacts with water
tail = hydrophobic - made up of hydrocarbons
what happens when many phospholipids interact with water
create spherical clusters with tails facing inwards to shield themselves from the water with their glycerol heads
forms a bilayer/micelle
what does the phospholipid bilayer make up
cell surface membrane
what are some features of the phospholipid bilayer
selectively permeable - allows small, non-polar molecules to cross
has a hydrophobic barrier won’t allow large non-polar/polar to cross
why is the fluid mosaic model named this way
membrane is fluid and has a mosaic like arrangement of proteins
how much mass of a membrane is made up of proteins
between 25% and 75%
what kind of proteins are in the membrane
integral and peripheral proteins
what are integral proteins and what do they do
they span the width of the membrane and help to transport substances that cannot diffuse across the membrane but are still vital to the cells functioning
eg glucose through carrier protein through facilitated diffusion
what a peripheral proteins and what do they do
confined to inner and outer surface of the membrane
may be free or bound to an integral protein
proteins on the extracellular side of membrane act as transmitters/involved in cell recognition
what are glycoproteins
protein molecules with polysaccharides attached
what factors affect membrane fluidity
cholesterol and temperature
how does cholesterol affect membrane fluidity
vital in controlling membrane fluidity
the more cholesterol, the less fluid - more rigid and less permeable
has a hydrophobic region so its able to create a further barrier to polar substances moving through its membrane
binds to hydrophobic tail of a phospholipid, causing them to pack more closely together which restricts their movements
helps maintain shape of animal cells - RBCs
how does temperature affect membrane fluidity
temp below 0 degrees - increases permeability, phospholipids are packed closely together and the membrane is rigid, channel and carrier proteins denature and ice crystals form which could pierce the membrane
temp between 0-45 degrees - phospholipids can move and aren’t as tightly packed, membrane is partially permeable, as temp increases phospholipids can move more because they have more energy
temps above 45 - phospholipid bilayer starts to melt, water inside cells expands which putting more pressure on membrane, the channel and carrier proteins denature
define facilitated diffusion
the overall net movement of molecules and ions from a region of high concentration to a region of low concentration down a concentration gradient
what is the type of some proteins that are involved in facilitated diffusion
carrier proteins
what happens when an ion/molecule binds to a carrier protein
it changes shape and therefore the molecule is able to cross the molecule
what is another name for diffusion
passive transport as it uses no energy
define active transport
movement of molecules/ions from an area of low concentration to an area of high concentration against a concentration gradient, using energy from ATP
where is the energy for active transport sourced from
adenosine triphosphate
how is ATP formed and how is it used
- it is formed during respiration, the breakdown of energy store molecules
- the substances to be transported across the membrane binds to the carrier protein
- one phosphate group is removed from ATP by hydrolysis and ADP forms
- a small amount of energy is required to break the bond holding the end phosphate in ATP
- once removed, phosphate group becomes hydrated
lots of energy is released as bonds form between water and phosphate
how is a phosphate group removed from ATP
hydrolysis
what is ADP
adenosine diphosphate
how is active transport sometimes referred to as
pumping
the pumping of substances across membranes that occurs in every cell
what is a glycolipid
a lipid with polysaccharides attached via glycosidic bonds
what processes are used when large molecules/quantities of molecules need to be transported across a membrane
endocytosis
exocytosis
what is a vesicle
small membrane bound sacs containing substance
what is the process of exocytosis
vesicles fuse with the cell membrane and the contents are released
what is an example of exocytosis
insulin is released to the blood via exocytosis
what is the process of endocytosis
- substances are taken into the cell by the creation of a vesicle from the cell surface membrane
- part of the membrane engulfs the solid/liquid material to be transported
- in some cases, the substances which is to be absorbed, attaches itself to a receptor in the membrane and is then absorbed by endocytosis
what is an example of endocytosis
cholesterol being taken in by cells
white blood cells ingesting bacteria
Describe how the primary structure of leptin enables it to be soluble in water.
primary structure determines the folding of polypeptide
forming globular structure
hydrophilic r groups located on the outside of the protein
water forms hydrogen bonds with the protein
Gene drives can be used to ‘force almost any genetic trait through a population’
Multiple genetic crosses were carried out between individuals homozygous for a recessive allele and individuals heterozygous for the same gene.
Describe how the outcome of these crosses would be affected if a gene drive was used with the recessive allele.
without the gene drive, expected outcome would be 50% heterozygous and 50% homozygous recessive offspring
with a gene drive, the proportion of individuals with homozygous recessive alleles would increase
the stronger the gene drive, the greater the proportion of homozygous recessive
People with cystic fibrosis require a higher energy diet than people without cystic fibrosis.
They are also more likely to develop problems in the pancreas.
Men with cystic fibrosis are less likely to be able to release sperm.
Discuss why a person with cystic fibrosis could have these symptoms
mucus stickier than normal
digestive enzymes cannot enter intestine as pancreatic duct is blocked with mucus
high energy diet is required as digestion is less efficient
pancreatic enzymes trapped behind mucus damage pancreatic cells - some insulin producing
pancreatic cysts can form
sperm can’t leave as sperm duct blocked with mucus
gene mutation - non-functioning CFTR channel protein so chloride ions cannot move out of epithelial cell
accumulation of sodium and chloride ions in cells causing water to move out of mucus via osmosis
Explain why cystic fibrosis affects the rate of oxygen uptake in the lungs.
chloride ions cannot leave the cell
sodium ions do not move out of the cell
therefore water moves into cell via osmosis
Describe how nucleotides join together to form DNA.
condensation reactions which form phosphodiester bonds using DNA polymerase
explain why Meselson and Stahl accepted one of the models for DNA
replication and rejected the other
conservative model was rejected/ semi-conservative was accepted
due to generation 1 having a single band halfway between N14 and N15
because DNA has one strand containing N14 and one strand N15
further generations would also have no band at N15
These new antibiotics attach to a site on the ribosome not affected by any known
antibiotics.
Deduce why these new antibiotics might be used to treat bacteria that are resistant to other antibiotics.
bacteria haven’t been exposed to new antibiotics before
bacteria have developed resistance to other antibiotics due to natural selection
therefore no mutation present to give resistance
Scientists have isolated these new antibiotics and tested their effectiveness against bacteria that are resistant to other types of antibiotic.
Devise a laboratory procedure to compare the effectiveness of penicillin with one of the new antibiotics.
prepare agar plates with bacterial cultures
prepare solutions of new antibiotic and penicillin
place onto paper discs
control time + temp of incubation
same concentration and volume of both antibiotics
measure area of inhibition
repeat for effective antibiotics
Describe the role of the CFTR protein in ensuring that the mucus produced in the lungs has the right consistency.
chloride ions leave cells
sodium ions leave cell
increasing solute concentration in mucus
water moves out of cells via osmosis
Describe the roles of transcription and translation in the synthesis of a globular protein by a muscle cell.
the gene for the protein in transcribed
complementary base pairing betwee RNA nucleotides and DNA
mRNA leaves the nucleus and attaches to a ribosome
pairing between codons on mRNA and anticodons on tRNA
tRNA provides specific amino acids
the sequence of bases determines the sequence of amino acids
Explain why different mutations in the CFTR gene can lead to differences in the
severity of the symptoms of cystic fibrosis.
different mutations will have different effects on the protein
chloride ion transport affected by the extent of changes to the CFTR protein
varying stickiness of mucus
Doctors give dietary supplements and digestive enzymes to children with cystic fibrosis.
Dietary supplements include carbohydrates, proteins and lipids, as well as vitamin and mineral supplements.
Explain why these children would be given dietary supplements and digestive enzymes.
cystic fibrosis causes production of stickier mucus
which blocks pancreatic duct
prevents enzymes digesting carbohydrates in intestines
reduced absorption of products of digestion into the blood
reduced vitamins = slower growth rate
dietary supplements would increase growth rate
Explain what is meant by an inherited recessive disorder.
caused by a faulty allele
that is only expressed in the absence of a normal allele
Individual 12 is pregnant and wants to know if her baby has alkaptonuria.
State and justify a suitable method of collecting cells for prenatal testing
CVS - cells taken from the placenta between 10-14 weeks of pregnancy
earlier diagnosis is beneficial
Explain why ATP is required for the movement of sodium ions into the cell.
sodium ions are being moved against concentration gradient
using active transport
Describe how glucose moves into cells by facilitated diffusion
carrier protein
moves from a high conc to a low conc
glucose binds to a carrier protein
Explain how the structure of glycogen allows it to be an energy store.
polymer of glucose
to provide glucose for respiration
branched for rapid hydrolysis
The phospholipid bilayer is important in controlling the movement of
molecules through the membrane.
Explain how the structure of a phospholipid molecule contributes to the
partial permeability of a cell surface membrane.
contains polar phosphate heads and non-polar fatty acid chains
allows non-polar molecules to pass through the membrane
polar molecules can’t move through
Explain how phospholipids form a cell surface membrane.
hydrophilic parts associate with water
hydrophobic part repel water
bilayer forms with hydrophobic parts pointing towards each other
Explain why the phospholipids are arranged in two layers in a cell surface membrane.
hydrophilic region orientated towards water
hydrophobic regions away from water
two layers as aqueous solution is on both sides of cell membrane
Describe the function of carrier proteins in a cell surface membrane.
involved in facilitated diffusion
movement of polar molecules
from a high conc to a low conc
involved in active transport
needs atp to move molecules against conc grad
Explain one way in which an investigation on effects of changing the concentration of sodium chloride solution on the mass of onion tissue could be improved
same age/type of onion increases repeatability and validity
How many times does an oxygen molecule cross a cell surface membrane to move from the centre of an alveolus to the centre of a red blood cell?
5
Describe why single-celled organisms, such as Valonia ventricosa, do not need a
specialised gas exchange surface.
can rely on diffusion to take in oxygen
large SA:V ratio
short diffusion distance
Describe the structure of the cell surface membrane.
mainly phospholipids + proteins
phospholipids form a bilayer
fluid-mosaic model
proteins may span the bilayer
