Random questioning Flashcards
Explain the process of DNA replication
- DNA double helix must first be unzipped and the hydrogen bonds between complementary base pairs broken. (DNA helicase)
- The exposed single-stranded DNA acts as a template to which free nucleotides can pair through complementary base pairing.
The enzyme DNA polymerase then joins the nucleotides together through condensation reactions.
This creates phosphodiester bonds between adjacent nucleotides producing a new sugar-phosphate backbone.
The action of DNA polymerase results in the synthesis of two identical molecules of DNA.
Each molecule is composed of one old strand and one new strand, and so the method of DNA replication is semi-conservative.
What can be used as evidence for proving the semi-conservative replication of DNA?
- E. colibacteria were grown on a medium containing only 15N. These bacteria only incorporated 15N into their DNA
- A control colony of bacteria was also grown on a medium containing the lighter 14N. These bacteria only incorporated 14N into their DNA
- Some bacteria were then transferred from the 15N medium to the lighter14N medium
- The bacteria were grown for enough time to undergo one round of replication
- The DNA of all three bacterial colonies was extracted
- The mass of the DNA molecules was compared by centrifuging the extracted DNA in a special solution. The heavier the DNA, the nearer the bottom of the tubeit collected
The results were as follows:
• The light DNA (control colony grown in 14N medium) collected in a band near the top of the centrifuge tube
• The heavy DNA (parent colony grown in 15N medium) collected in a band near the bottom of the centrifuge tube
• The DNA from the transferred bacteria collected in the middle of the centrifuge tube
This provided conclusive evidence that each replicated DNA molecule must contain both heavy and light strands, supporting the semi-conservative replication model.
( Meselson and Stahl )
What is ATP and what is it composed of?
It is a phosphorylated nucleotide composed of organic base adenine, ribose sugar and 3 phosphate groups
What 3 ways can ATP be synthesised?
- during photosynthesis using light energy (photophosphorylation) occurs in chloroplast in plant cells
- by using energy from electron transfers during respiration ( oxidative phosphorylation) occurs in mitochondria in plant and animal cells
- by transferring Pi from donor molecules to ADP during respiration (substrate level phosphorylation) occurs in cell cytoplasm and mitochondria of plant and animal cells
Explain with references to changes in protein shape how reaction with ATP might cause a channel protein to open or close.
ATP is often hydrolysed by channel proteins to form ADP and Pi releasing energy.
ADP and Pi have different charge profiles to ATP’s so the hydrolysis reaction could cause the channel protein to open or close because ADP and Pi could interact with the ionic bonding in the proteins tertiary structure, affecting the 3D shape.
The released energy could also affect the secondary or tertiary bonding in the protein.
Explain how DNA polymerase utilises triphosphate in the replication of DNA
Phosphodiester bonds must be formed between adjacent free acitivated nucleotides in DNA replication.
The activated nucleotides are nucleoside triphosphate.
The formation of the phosphodiester bonds requires energy, which is provided by the hydrolysis of the “unstable” covalent bonds between the phosphate groups of the activated nucleotides.
ATP serves as a great immediate energy source because?
- Energy can be supplied to the cell in optimal amounts
- ATP hydrolysis is a single reaction that occurs easily due to unstable bonds - Energy can be supplied to the cell in optimal amounts
- ATP hydrolysis only releases a small. manageable amount of energy so less is wasted as heat
What can the energy released by ATP hydrolysis be used for?
To drive biological processes :
- metabolic processes (synthesise biological molecules e.g carbohydrates_
- Active transport (ATP is used to change the shape of carrier proteins
- Movement ( ATP is used for muscle contraction)
- Secretion (ATP is needed for the formation of vesicles which will then be released from the cell)
- Molecule activation (ATP is used to phosphorylate other molecules to make them more reactive)
Tears have a high concentration of salt in them,
describe how tears might act as an antibacterial (using knowledge of water potential)
- Tears could have a water potential thats more negative than the bacteria.
- When bacteria comes into contact with tears, water may therefore move out of the bacteria by osmosis.
- This can affect rates of bacterial metabolic reactions hitch can slow or stop growth and/or survival
Why do the eyes require tear fluid, but it isnt present on the skin?
The skin is protected by a layer of dead cells but the outermost layer of cells in the eye is alive.
Cigarette smoke contains chemicals that can paralyse cilia. Explain why smoking leads to increased lung infections.
- Cillia wafts mucus (which traps pathogens) up to the top of the throat so they can be swallowed and sterilised by the stomachs HCL.
- Paralysed cilia cannot move the mucus so it sits in the bronchi/bronchioles for longer giving pathogens a longer window of opportunity to infect the cells of the lung
Explain what is meant by degeneracy in the genetic code and how degeneracy could be advantageous to organisms
(define degeneracy then explain how that helps)
“Degeneracy” means that different codons can code for the same amino acid. This could be protective against mutations as there is a chance a codon could undergo a mutation (base substitution) to become another coding for the same amino acid (silent mutation)
tRNA is a very short RNA molecule made of around how many nucleotides?
80
Despite tRNA being single stranded, how does it still fold into a clover leaf shape?
tRNA can form complementary base pairs with itself, folding into a clover-leaf shape
What section on a tRNA molecule do the amino acids attach to?
One end of the tRNA molecule extends further out, with its bases faced outwards, providing a site for amino acid attachment
How many variety tRNA molecules can bind to the mRNA codons?
61 mRNA codons (not 64 because 3 code for stop)
What happens to a ribosome once an mRNA has successfully translated its polypeptide?
The ribosome units separate form the mRNA strand and are quickly resused for another round of translation
Which enzyme catalyses the linkage of adjacent RNA nucleotides during transcription in eukaryotes?
RNA polymerase
What is an mRNA codon?
Each 3 bases of the mRNA sequence that corresponds to a single amino acid
What is required to form peptide bonds between adjacent amino acids during translation?
ATP is required to form the peptide bond between 2 adjacent amino acids during the process of translation t the ribosomes
mRNA leaves the nucleus by travelling through?
Nuclear pores.
mRNA is much smaller than a chromosome so it can be transported form the nucleus to the cytoplasm through nuclear pores
Which RNA base temporarily forms hydrogen bonds with adenine in a DNA sequence?
Uracil
What does RNA polymerase do?
RNA polymerase catalyses the formation of a strand of mRNA during transcription by joining adjacent RNA nucleotides.
What is the role of tRNA?
Transfer the genetic information from mRNA into a sequence of amino acids
The ribosome translates mRNA into the corresponding ….?
amino acid
What happens to the 1st tRNA molecule after the ribosome has moved forward and a peptide bond is formed between the 2 amino acids?
The ribosomes moves along the mRNA strand by exactly 3 base pairs and the 1st tRNA is released. It is free to go and bind to another amino acid in the cell, tRNAs are recycled.
What happens to the structure of a polypeptide after it is released from the ribosome?
It folds into a specific tertiary structure determined by the amino acid sequence.
Compare the structure of DNA to that of mRNA
- DNA is double stranded but mRNA is single stranded.
- DNA contains bases adenine, thymine, cytosine and guanine WHILST RNA has uracil instead of thymine
- DNA has deoxyribose sugar and RNA has ribose sugar
Describe the process of translation
- The mRNA associates with a ribosome by binding to the small subunit at the start codon.
- The first tRNA molecule (carrying amino acid methionine) then binds to the start codon by hydrogen bonding.
- The tRNA’s anticodon is complementary to the mRNA start codon.
- Once this first tRNA has bound to the start codon, the large ribosomal subunit binds.
- The second tRNA binds as it holds anticodons complementary to the 2nd codon of mRNA, and carries the amino acid specified by that codon.
- A condensation reaction takes place forming a peptide bond between the 2 amino acids, this also releases the methionine from the 1st tRNA
- The ribosome then moves forward 3 bases and the 2st tRNA is released.
- This continues extending the peptide by one amino acid each time, eventually a polypeptide will have been formed.
- Translation stops when the stop codon is reached. (this codon has no complementary tRNA.
- The subunits of the ribosome separate releasing the polypeptide.
How does cholesterol prevent the cell membrane from becoming too stiff?
Cholesterol prevents the cell membrane from becoming too stiff by preventing the phospholipids from grouping too close together
What is meant by. a partially permeable membrane?
It can control what passes into and out of cells. Some substances can pass through the membrane and others are prevented from passing.
Vaguly, how do particles cross the cell surface membrane with carrier proteins?
Carrier proteins transport specific molecules across the membrane by changing shape when the molecules bind to the protein.
What properties of cholesterol allow it to fit into the phospholipid bilayer?
small, and has hydrophobic and hydrophilic ends
What type of channels do channel proteins form?
Hydrophillic channels that allow specific water-soluble molecules to pass through the membrane
What is the function of cholesterol in the bilayer?
Wedges of cholesterol are inserted into the lipid bilayer to help regulate the fluidity of the membrane
How do components of the cell membrane move?
sideways along the membrane
What are 3 roles of peripheral proteins on the surface of the cell surface membrane?
cellular adhesion, recognition site, receptor molecule
How would proteins move in the membrane?
molecules can move laterally in the plasma membrane. This is because of the fluid mosaic structure of membranes - phospholipids and embedded proteins do not form strong or rigid bonds with each other.
How would the ratio of saturated to unsaturated phospholipids affect the fluidity of the membrane?
If there was higher saturated to unsaturated phospholipids in the membrane then fluidity would decrease. This is because unsaturated phospholipidsare ‘kinked’ preventing the close packing of molecules in the membrane decreasing the potential for compression
Explain what would happen to the speed of light sensing at low temperatures if the membrane of retinal cells had a low cholesterol content.
Cholesterol maintains fluidity at low temperatures. x protein and y protein must move around in order to interact and facilitate light sensing. This is quicker when the membrane is more fluid - so a low cholesterol content would slow light sensing at low temps
Describe the structure of the cell surface membrane with reference to the fluid mosaic model
mark 1. mention phospholipid bilayer
mark 2. describe the structure (hydrophilic polar phosphate head outwards, hydrophobic non-polar fatty acid tail inwards creating bilayer)
mark 3. mention cholesterol regulating the fluidity of the membrane
mark 4. protein channels (facilitate molecules in/out cell) carrier proteins (actively transport molecules in/out cell using ATP)
mark 5. glycoproteins and glycolipids have signalling roles
mark 6. describe how it is a fluid mosaic model
How do cell membranes selectively control which particles enter or leave the cell?
Channel and carrier proteins are specific to one type of particle. Cell membranes can therefore selectively control which particles can enter or leave the cell by which proteins are found on their membrane.
Where does tissue fluid drain?
into the lymphatic system and blood capillaries at the venous end of a capillary bed.
Why do foetal haemoglobin have a slightly higher affinity for oxygen than adult haemoglobin?
To ensure that the developing foetus can receive oxygen across the placenta
How much of carbon dioxide transported in the blood is dissolved directly in the blood plasma?
5%
Why does the transportation of carbon dioxide in the blood cause haemoglobin to have a lower affinity for oxygen?
The lower pH levels in the cell causes a conformational change in the tertiary structure of haemoglobin, making it harder for the oxygen molecules to bind to it.
What is the endothelium?
thin, inner layer of cells of the blood vessels
What is the role of arteries?
To carry away blood from the heart at high pressure
What blood vessel can help to control the flow of blood through the body?
Arterioles can contract their smooth muscle, thereby constricting their lumens. This controls the flow of blood through the body
From where and where to do venues deliver blood?
Venules deliver blood from the veins to the capillary beds.
What is the role of tissue fluid?
Animals with closed circulatory systems bathe their body tissues in tissue fluid.
Tissue fluid is used to exchange nutrients and gasses between cells of the body and the blood in the circulatory system.
What forces blood plasma through the capillary endothelium into existing tissue fluid?
High hydrostatic pressure
What causes the flow of lymph fluid in the lymphatic system?
Using a combination of hydrostatic pressure from the lymph capillaries and contraction of skeletal muscle.
Where is tissue fluid formed?
Arterial end of a capillary bed
How does the oncotic pressure of tissue fluid change from the arterial to the venous ends of a capillary bed?
It doesnt change.
Oncotic pressure remains constant in the tissue fluid.
Compare the structure of arterioles to arteries
arterioles have similar structure to arteries but they are smaller and have relatively thinner muscles and elastic layers
Why do arterioles not require as much elastic layers / thinner muscles?
Because the blood pressure is decreasing
What is the main role of arterioles?
Contraction of smooth muscle (limiting the diameter of the vessel) constricts the arterioles and controls the flow of blood through the body
Describe the structure of capillaries
They have very thin walls consisting of just a single-celled layer of endothelium
Why is the lumen of capillaries narrow?
To squeeze red blood cells against the endothelium to improve transfer of oxygen.
Also the diffusion pathway of co2 or o2 is very short.
Gas / nutrient exchange is at maximum efficiency.
