Stuff to know Flashcards
Describe the steps of protein synthesis
1) An mRNA copy of the DNA is made in the nucleus via transcription
2) Proteins are synthesised in ribosomes on the RER via translation
3) Proteins undergo modification at the Golgi apparatus, where lipids or carbohydrates may be added
4) Some proteins are secreted from the cell membrane when transport vesicles fuse with cell surface membrane, some proteins work within the cell
what ribosomes do prokaryotes have?
70s
what ribosomes do eukaryotes have?
80s
Does a SEM have a lower resolution than TEM?
Yes
What is the resolution of a light microscope?
0.2 micrometres
what is the magnification of a light microscope?
X 1500
micrometers to centimetres?
/ 10,000
centimetres to millimetres?
X 10
micrometres to millimetres?
/ 1000
micrometres to nanometres?
X 1000
how do you calculate magnification?
image size/ actual object size
What are the advantages of cell staining?
- Makes the cell easier to see
- Increases the contrast
- Allows you to recognise the different parts of a cell
Describes the roles of the cytoskeleton
- Maintaining the shape of the cell
- The movement of the cillia
- Changing the shape of the cell (exocytosis, phagocytosis, pseudopodia)
- Movement of vesicles to plasma membrane
- The formation of the spindle fibres during mitosis
- Holding organelles in place
What are the roles of membranes within cells?
- compartmentalisation
- Isolation of the contents of the organelle i.e the hydrolytic enzymes.
- Site for the attachment of enzymes
- Controls what enters and leaves an organelle
- Creates concentration gradients
What is the secondary structure ?
-Hydrogen bonds form between the amino acids all along the polypeptide chain (this is due to the polarity of the CO and the NH groups).
-These hydrogen bonds cause the polypeptide chains to twist and fold into shapes .
-The twisted 3d shape formed can either be an alpha helix cylindrical shape or a beta pleated sheet .
-Both these structures are maintained by hydrogen bonds
What are globular proteins?
Proteins that have a roughly spherical shape
What are glucose and fructose?
Monosaccharides
What 2 polysaccharides are starch molecules made up of?
Amylose and amylopectin
What are examples of monosaccharides?
Glucose, galactose, fructose, ribose, deoxyribose, glyceraldehyde
What type of bond forms when monosaccharides like glucose bond?
Glycosidic bond
What make up maltose?
Alpha glucose + alpha glucose
What forms sucrose?
Alpha glucose + fructose
What is the molecular formula of sucrose?
C12 H22 O11
What forms lactose?
Alpha glucose + galactose
What does sucrose and sucrase make?
Alpha glucose + fructose
Is amylose a monosaccharide or a polysaccharide?
Is amylose a monosaccharide or a polysaccharide?
Is amylopectin a monosaccharide or a polysaccharide?
A polysaccharide
What is amylose?
A polymer of glucose joined by a -1,4- glycosidic bonds. Amylose is unbranched and helical
What is amylopectin?
polymers of glucose joined by -1,4- glycosidic bonds but with branches of 1,6 glycosidic bonds. This causes the molecule to be branched rather than helical
What is glycogen made up of?
Alpha glucose molecules with much shorter 1,4 chains and many more branches of alpha 1,6 glycosidic bonds than amylopectin
What reactions form the ester linkage?
Condensation reactions
What are the roles of lipids?
-Energy storage
-Insulation(electrical and thermal)
-Buoyancy(floating)
-Waterproofing
-Protection
-Membranes
-Source of water- from respiration
-Aids absorption
What is a difference between lipids from animals and those from plants?
Lipids from animals are saturated, whereas lipids from plants are unsaturated
what can the hydrophilic hydroxyl group on the cholesterol molecule interact with?
the head groups of phospholipids. the rest of the cholesterol molecule can interact with the hydrophobic fatty acid tails
what are the functions of cholesterol?
- producing steroid-based hormones.
- making vitamin D, this process takes place in the skin in response to ultraviolet light.
- producing bile in the liver.
- fluidity and permeability of cell membranes
What prosthetic group does haemoglobin have?
Haem, which binds to oxygen
What is a protein with a prosthetic group called
A conjugated protein
What are disulfide bonds?
strong covalent bonds that form between two cysteine R groups (as this is the only amino acid with a sulphur atom)
What is the strongest protein bond?
The disulfide bond
In which proteins are disulfide bonds common in?
proteins secreted from cells eg. insulin
Where do Ionic bonds form in a protein?
Ionic bonds form between positively charged (amine group -NH3+) and negatively charged (carboxylic acid -COO-) R groups
Where do hydrophobic interactions form?
between the non-polar (hydrophobic) R groups within the interior of proteins
What is a good way of distinguishing between fibrous and globular proteins?
SAFES (Shape, Amino acid sequence, Function, Examples and Solubility).
How do you calculate Rf values?
Rf value = distance travelled by sample / distance travelled by solvent
what type of covalent bond is present in proteins?
peptide
what type of covalent bond is present in lipids?
ester
what type of covalent bond is present in nucleic acids?
phosphodiester
what do reducing sugars do?
donate electrons and they reduce the soluble copper sulphate to insoluble brick-red copper oxide
what do non-reducing sugars do?
they cannot donate electrons, therefore they cannot be oxidised
summarise the test for proteins
1) Add sodium
hydroxide solution.
2) Add copper (II)
sulphate solution.
Colour change should be from blue to purple
summarise the test for starch
1) Add iodine in
potassium iodide
solution.
Colour change from
brown-orange to
blue-black.
summarise the test for lipids
1) Add ethanol.
2) Pour solution into
water.
A cloudy emulsion forms
summarise the test for reducing sugars
1) Add Benedict’s
reagent to a sample and
heat in a water bath
that’s brought to a boil.
Sample goes from blue to
green to yellow to orange
to brick red precipitate,
depending on the
concentration
summarise the test for non reducing sugars
1) Add dilute HCl.
2) Put in a water bath
brought to a boil.
3) Neutralise with
sodium hydrogen
carbonate.
4) Do Benedict’s Test
for reducing sugars.
Sample goes from blue to
green to yellow to orange
to brick red precipitate,
depending on the
concentration
summarise the test for glucose
1) Dip test strip in
solution.
Colour change will occur
if glucose is present.
Compare to chart of
known colour changes to
check for concentration.
What are the functions of hydrogen ions?
-hydrogen bonding
-ATP formation
-control of blood pH
-transport of carbon dioxide
What are the functions of calcium ions?
-bone and enamel structure
-cofactor in blood clotting
-synaptic transmission of nerve impulses
-muscle contraption
What are the functions of iron ions?
-transport of oxygen via haemoglobin
-transfer of electrons
What are the functions of sodium ions?
-electrolyte
-nerve transmission
-reabsorption of water into the kidneys
What are the functions of potassium ions?
-electrolyte
-nerve transmission
-reabsorption of water into the kidneys
-opening of the stomata
What are the functions of ammonium ions?
deamination of proteins
What are the functions of nitrate ions?
source of nitrogen for plants
What are the functions of hydrogen carbonate ions?
carbon dioxide transport in the blood
What are the functions of chloride ions?
maintaining pH balance during carbon dioxide transport
What are the functions of phosphate ions?
-component of the cell membrane(phospholipids)
-component of bones (calcium phosphate)
-component of ATP and nucleic acids
What are the functions of hydroxide ions?
bonding between biochemical molecules
What is the structure of collagen?
-Peptide bonds between amino acids
-Secondary structure is alpha helix
-Has high proportions of glycine
-3 polypeptide chains and hydrogen bonds between them
-No hydrophilic R groups on the outside of the molecules
-Adjacent molecules joined by crosslinks
-Crosslinks form fibrils
What is the structure of heamoglobin?
-Peptide bonds between amino acids
-Secondary structure is alpha helix, with small regions of beta pleated sheets.
-Hydrophilic R groups on the outside of the molecule
-4 polypeptide chains, 2 alpha, 2 beta
-4 haem groups per molecule
-Made up of a wider range of amino acids
Describe the ways in which the structure of collagen is similar to the structure of haemoglobin?
-Both have an acid amino chain
-Both have amino acids joined by peptides
-Both helical
-Both have a quaternary structure
-Both have more than 1 subunit
How does heamoglobin differ from collagen?
-Haemoglobin is globular, whereas collagen is fibrous.
-Haemoglobin has hydrophilic R groups on the outside, whereas collagen doesn’t.
-Haemoglobin has 4 polypeptide chains, whereas collagen has only 3.
-Haemoglobin has a high wider range of amino acids- not predominantly glycine like collagen is
What are the differences between glycogen and cellulose?
-Glycogen doesn’t have hydrogen bonding, whereas cellulose does.
-Glycogen has a- 1,4 bonds and a-1,6 bonds; whereas cellulose only has a-1,4 bonds.
-Glycogen is branched, whereas cellulose is helical.
-Glycogen doesn’t have fibrils, whereas cellulose does have fibrils.
-Glycogen has granules, whereas cellulose does not have granules.
-All glucose units in glycogen are in the same orientation, whereas adjacent glucose units in cellulose are in opposite orientation.
Why does glycogen make a good storage molecule?
- Glycogen is insoluble, so it doesn’t affect the water potential of the cell.
- Can be broken down easily.
- Has many branches for enzymes to attach to.
- It’s compact and so stores a lot of energy
What does methylene blue do?
stains the nuclei in animal cells to give contrast(stains blue)
What does crystal violet do?
It stains cell walls purple
What is the magnification?
How much bigger an image is than the specimen
What is the resolution?
The ability to clearly distinguish 2 points that are next to each other
What is specific heat capacity?
The amount of heat required to raise the
temperature of 1Kg of liquid by 1oC.
Why does it take a lot of energy to raise the temperature of water?
Because water has a very high specific heat capacity. This allows water to provide a very thermally stable environment for organisms to live in.
What is the specific heat capacity of water?
4200 J/Kg degrees Celsius
what is cohesion?
a force where water molecules stick together.
What is adhesion?
The attraction between non alike molecules
Why is the ability of water to act as a solvent important for the survival of organisms?
- Allows for metabolic reactions to occur
- Allows for transport in transport systems, such as the xylem, to occur.
- Allows for the dilution of toxic substances
Water has a high specific heat capacity so….
- A large amount of energy is needed to change the temperature of water.
- So, a thermally stable environment is provided for aquatic organisms because their internal body temperature will only change slowly, so metabolism will function correctly
What is the latent heat of vaportisation?
- the amount of heat energy required to vaporise a liquid
Water has a high latent heat of vaporisation so…
- a large amount of energy is required to change water from a liquid to a gas.
- this allows for evaporation to be an efficient cooling mechanism i.e sweating can cool organisms down.
Ice is less dense than water so….
- The surface of ice provides habitats for organisms like polar bears.
- The water beneath ice doesn’t freeze so aquatic organisms can swim beneath the ice
Water is an effective solvent so..
it is a medium for metabolic reactions
Water has high surface tension so….
it is a habitat for insects
water has a high density so…
this allows for certain organisms to float on water’s surface
What are the components of nucleotides?
A pentose sugar , either ribose or deoxyribose, a nitrogenous base, and a negatively charged phosphate group
What structure do purines have?
A double ring structure
Give some examples of purines
Adenine and guanine
What is the structure of a pyrimidine?
A single ring structure
What are some examples of pyrimidines?
Thymine and cytosine and uracil
What are the bases found in RNA?
Adenine, uracil, guanine and cytosine
What base replaces thymine in RNA?
Uracil
What bond forms between the phosphate group of one nucleotide and the hydroxyl group on the carbon 3 of the other nucleotide?
A phosphodiester bond
what does guanine pair with?
cytosine
what does adenine pair with?
thymine
what do purines pair with?
pyrimidines
how many hydrogen bonds do guanine and cytosine form?
3
how many hydrogen bonds do adenine and thymine form?
2
What are the steps or DNA replication?
-The enzyme DNA helicase attaches to the DNA molecule. DNA helicase causes the hydrogen bonds between complementary bases to break. This causes the 2 polynucleotide strands to separate from each other.
-Free nucleotides line up with their complementary bases on the DNA strands. At this stage, the free nucleotides are only held in place by hydrogen bonds between complementary bases, not phosphodiester bonds. The nucleotides are called activated nucleotides, as they have 3 phosphate groups.
-The second enzyme, DNA polymerase, moves up and down the polynucleotides and catalyses the formation of phosphodiester bonds between the activated nucleotides. This is a condensation reaction. When the phosphodiester bonds form, the activated nucleotides lose their extra 2 phosphate groups and this provides the energy for the reaction.
Why is DNA replication an example of semi-conservative replication?
because each DNA molecule contains one strand from the original DNA molecule and one strand which is brand new
what is conservative replication?
where a DNA double helix is formed containing 2 new strands. The DNA molecule contains more of the original DNA
What is the most common isotope of nitrogen
Nitrogen-14
which isotope of nitrogen is heavier, nitrogen-14 or nitrogen-15?
nitrogen-15
What does the position of the DNA band determine?
How heavy the DNA is
Is the DNA in prokaryotes circular or linear?
Circular with no free ends
Is the DNA in eukaryotes circular or linear?
Linear with 2 free ends
What are the 2 main steps of protein synthesis?
Transcription and translation
Describe all the steps of DNA transcription
1) DNA helicase breaks the hydrogen bonds between the 2 polynucleotide strands of DNA.
2) Complementary nucleotides move into place and form hydrogen bonds with the bases on the exposed nucleotides of one of the DNA strands.
3) RNA polymerase then joins the RNA nucleotides by forming phosphodiester bonds.
4) A strand of mRNA is now produced
5) Now that the mRNA has been synthesised, the RNA polymerase detaches from the DNA and the DNA goes back to its normal double helix structure.
6) The mRNA now moves out of the nucleus through a nuclear pore.
7) Once in the cytoplasm, the mRNA can now undertake translation
Because of the fact that most amino acids have more than one triplet that codes for them, what do scientists call the genetic code?
The “degenerate code”
What is meant by the fact that the genetic code is non-overlapping?
No base is read more than once
What is meant by the fact the genetic code is universal?
The same base triplets encode the same amino acid in the vast majority of living organisms.
Describe the stages of protein translation
1) The small subunit of a ribosome binds with the mRNA at the start codon.
2) a tRNA molecule with an anticodon complementary to the start codon attaches. This is held in place by hydrogen bonds between the complementary base pairs on the mRNA and tRNA
3)Now, a second tRNA molecule moves into place. The anticodon on this tRNA is complementary to the second codon on the mRNA.
4)Now, a peptide bond forms between the 2 amino acids produced. This forming of the peptide bond is catalysed by the enzyme peptidyl transferase. The formation of the peptide bond requires energy provided by ATP
5)Now, the ribosome moves to the next codon and forms a peptide bond with the next amino acid. The first tRNA molecule is now released (TRNA molecules that have been released are later attached to their amino acids by enzymes in the cytoplasm)
6) The ribosome continues moving down the mRNA, forming the polypeptide
7)When the ribosome comes to a stop codon, it detaches and the protein is released.
Why is ATP a nucleotide?
Because it contains 3 phosphate groups, a ribose sugar and the base adenine
What is the reaction that involves adding a phosphate back onto ADP called?
A phosphorylation reaction
What are anabolic reactions ?
Reactions that build larger molecules from smaller molecules
How many different codons (triplets) are possible?
64 (there’s 4 bases)
Does semi Conservative replication occur in preparation for mitosis?
Yes
Does the degenerate nature of the genetic code limit the amount of mutations possible?
Yes
What are the advantages of Complementary Base Pairing?
-Allows for identical copies of DNA to be produced.
-Prevents mutations.
-Allows DNA to be replicated without error.
Why does the fluid mosaic model describe cell membranes as fluids?
because…
-The phospholipids and proteins can move around via diffusion
-The phospholipids mainly move sideways, within their own layers
-The many different types of proteins interspersed throughout the bilayer move about within it (a bit like icebergs in the sea) although some may be fixed in position
how can phospholipids be chemically modified to act as signalling molecules?
by….
-Moving within the bilayer to activate other molecules (eg. enzymes)
-Being hydrolysed, which releases smaller water-soluble molecules that bind to specific receptors in the cytoplasm
describe intrinsic proteins
they’re fully embedded in the membrane from one side to the other. Because they pass right through the bilayer, intrinsic proteins have hydrophobic amino acids on the outside surface of the protein. These can interact with the hydrophobic fatty acid tails in the phospholipid bilayer.
what are 2 types of intrinsic protein?
carrier proteins and protein channels
describe protein channels
they run through the centre of the phospholipid bilayer. This channel is lined with hydrophilic amino acids and is filled with water molecules. They allow water -soluble molecules and ions to diffuse through (hydrophilic substances)
describe carrier proteins
they have a binding site for certain chemicals . When that chemical binds, it causes the tertiary structure of the carrier protein to change. This change in tertiary structure brings the chemical across the membrane where the chemical is now released
describe extrinsic proteins
they don’t span the membrane and are found on one side of the membrane or the other. They can sometimes be attached to intrinsic proteins
describe the functions of extrinsic proteins
- some play a structural role within the membrane.
- some act as enzymes
- some are receptors for other molecules, such as hormones
what are glycoproteins?
membrane proteins attached to a carbohydrate molecule
what are the functions of glycoproteins?
- allowing cells to attach to each other to form tissues such as nervous tissues
- presenting antigens to T cells
- acting as receptors for hormones
what are glycolipids?
carbohydrates attached to phospholipid molecules
what are glycolipids used for?
- contacting other cells. the glycolipids of one cell can be recognised by another cell and this can determine whether cells come into contact .
- they act as antigens e.g in determining blood groups
what 2 factors affect the permeability of the cell membrane?
temperature and solvent concentration
what happens to the lipids when the temperature of the phospholipid bilayer increases?
- The lipids become more fluid and so the cell membrane becomes a less effective barrier to polar molecules and so they can easily pass through.
- Diffusion takes place at a higher speed due to increased kinetic energy. So, more molecules pass through
what happens to the proteins in the cell membrane at really high temperatures (temperatures exceeding 40 degrees)?
the proteins in the cell membrane denature, which means that it can no longer form an effective barrier and so substances can freely pass through the disrupted membrane
why do organic solvents increase membrane permeability?
because they dissolve the lipids in the membrane, causing the membrane to lose its structure
why does membrane permeability also increase below 0 degrees Celsius?
-Increased permeability can be caused by channel or carrier proteins deforming at these low temperatures
-Ice crystals that form can also pierce the cell membrane, making it highly permeable
what is diffusion?
The net movement, as a result of the random motion of its molecules or ions, of a substance from a region of its higher concentration to a region of its lower concentration.
what factors is the rate of diffusion dependant on?
- concentration gradient
- surface area
- diffusion distance
how does the steepness of the concentration gradient affect the rate of diffusion?
The greater the difference in concentration between 2 areas, the greater the rate of diffusion
what does Fick’s Law state?
‘the rate of diffusion is proportional to both the surface area and concentration difference and the rate of diffusion is inversely proportional to the thickness of the membrane’.
what is the formula for the rate of diffusion?
rate of diffusion = surface area X difference in concentration / length of the diffusion path
what can increase the surface area of cell membranes?
folding e.g microvilli in the intestines or cristae in mitochondria
what 2 proteins enable facilitated diffusion?
Channel proteins
Carrier proteins
is facilitated diffusion a passive process?
yes
what is osmosis?
the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane
what is the unit of water potential?
kilopascals
what type of water has the highest water potential?
pure water
what is the water potential of pure water?
0kPa
What is the water potential of solutions besides pure water?
less than 0
do more concentrated solutions have higher or lower water potential than a less concentrated solution?
lower water potential
isotonic meaning?
the concentration of solutes is the same inside and outside of the cell, meaning the water potential is equal. water will diffuse equally between locations
hypertonic meaning?
the solution has a higher solute concentration than the cell, meaning the water potential is lower outside the cell. Water will diffuse out of the cell
hypotonic meaning
the solution has a lower solute concentration than the cell, meaning the water potential is lower inside the cell. water will diffuse into the cell
describe the visking tubing diffusion practical
-Fill a section of Visking tubing with a mixture of starch and glucose solutions
-Suspend the tubing in a boiling tube of water for a set period of time
-Test the water outside of the visking tube at regular intervals for the presence of starch and glucose to monitor whether the diffusion of either substance out of the tubing has occurred
-the results should indicate that glucose, but not starch, diffuses out of the tubing
what happens if an animal cell is placed in a solution with a lower water potential than the cell (such as a concentrated sucrose solution)?
- Water will leave the cell through its partially permeable cell surface membrane by osmosis.
- The volume of the cell will decrease.
- The cell will consequently shrink/shrivel up.
what happens when an animal cell is placed in a solution with a higher water potential?
water will enter the animal cell through its partially permeable cell membrane by osmosis. The volume of the cell will increase. The animal cell has no cell wall to withstand the increased pressure created. The cell membrane will stretch out too far and will eventually burst.
what happens to animal cells in an isotonic environment?
The movement of water molecules into and out of the cell occurs at the same rate (no net movement of water) and there is no change to the cells
why is the loss and gain of water less severe in plant cells?
because plant cells have a supporting cell wall
what happens if a plant cell is put in a solution with a lower water potential than the plant cell?
- water leaves the cell through the partially permeable membrane by osmosis.
- The volume of the plant will decrease.
- The protoplast will shrink and pull away from the cell wall. The cell is now plasmolysed
what happens if a plant cell is put in a solution with a higher water potential than the plant cell?
- water will enter the plant cell through the partially permeable membrane by osmosis.
- The volume of the plant cell will increase.
- The protoplast will expand and push against the cell wall.
- The cell wall withstands the increased pressure created. The pressure increases until the cell is rigid and firm (turgid). The cell becomes fully inflated with water and no more can enter
what is it called when a plant cell is fully inflated with water and has become rigid and firm?
it is called turgid
why is turgidity important for plants?
as the effect of all the cells in a plant being firm is to provide support and strength for the plant – making the plant stand upright with its leaves held out to catch sunlight
what happens if plants do not receive enough water?
the cells cannot remain rigid and firm (turgid) and the plant wilts
What is active transport?
The movement of molecules/ions from a region of lower concentration to a region of higher concentration. Active transport requires energy in the form of ATP
Describe the steps of active transport in a cell
1)Ions bind to receptors on the carrier protein.
2) A molecule of ATP binds to the carrier protein.
3) The ATP undergoes hydrolysis, producing phosphate and a molecule of ADP.
4) The phosphate now attaches to the carrier protein and causes it to change shape.
5)This shape change causes the carrier protein to transport the molecule or ion to the other side of the membrane where it is released.
6)The phosphate now unbinds from the carrier protein, causing the carrier protein to return to its original shape.
7) The ADP and phosphate will later reform ATP during respiration.
What is active transport important in?
- The reabsorption of useful molecules or ions into the blood after filtration into the kidney tubules.
- The absorption of some products or digestion from the digestive tract
- The loading of sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant.
- The loading of inorganic ions from the soil into root hairs
What are the 2 forms of bulk transport?
Endocytosis and exocytosis
What is bulk transport?
The use of active transport to move larger molecules and whole cells that cannot move through channel proteins
What is endocytosis?
The process by which the cell surface membrane engulfs material, forming an endocytic vacuole around it.
What are the 2 types of endocytosis?
Phagocytosis and pinocytosis
What is phagocytosis?
When material is taken into a cell in solid form
What is pinocytosis?
When material is taken into a cell in liquid form
What is exocytosis?
When materials are removed from or transported out of the cell in vesicles, which fuse with the cell membrane and release the materials out of the cell out of the cell
What is the role of the ileum in the small intestine?
To absorb the molecules produced by digestion. This includes glucose
How does the fact that the membrane of the microvilli is folded into a large number of microvilli help with the rate of diffusion and the rate of active transport?
This increases the surface area of the membrane, providing more space for the membranes needed for facilitated diffusion and active transport. So, both of their rates are increased.
What are enzymes?
Biological catalysts that increase the rate of reactions in living organisms
What reaction does catalase catalyse?
The breakdown of hydrogen peroxide into water and oxygen
What reaction does amylase catalyse?
The breakdown of starch into maltose
What reaction does trypsin catalyse?
The breakdown of proteins into peptides and amino acids
What is the induced fit model?
The idea that the tertiary structure of the active site actually changes as the substrate molecule binds with the enzyme. As the substrate starts to form bonds with the amino acids in the active site, the tertiary structure of the enzyme adjusts so that the active site moulds itself tightly around the substrate. This change in the tertiary structure of the enzyme ensures that the active site fits perfectly into the substrate.
What is Q10?
The temperature coefficient
What is the equation for the temperature coefficient?
Temperature coefficient= rate of reaction at temperature X at 10 degrees / rate of reaction at temperature X
What does the pH of a solution depend on?
The concentration of hydrogen ions (H+)
How do you workout the pH on a calculator?
pH = - log[H+]
How does a competitive inhibitor reduce the rate of reaction?
-The competitive inhibitor prevents the actual substrate from colliding with the active site.
-This reduces the frequency of successful collisions between the substrate and the active site.
-So less ESC’s are made and the reaction rate is lower.
What is succinate the substrate for?
An enzyme involved in respiration
What competitive inhibitor has a similar structure to succinate?
Malonate
What does malonate slow down the rate of?
Respiration
What is the name of a molecule that competes with substrate molecules for the active site?
A competitive inhibitor
Give 2 examples of competitive inhibitors
Methotrexate, which is a reversible competitive inhibitor used to treat certain cancers
Penicillin, which is an irreversible competitive inhibitor used to treat bacterial infections
Where do non competitive inhibitors bind?
To the allosteric site
What happens to the enzyme when the non competitive inhibitor bonds to the allosteric site?
The tertiary structure of the enzyme changes. This results in the shape of the active site changing and so the active site is no longer complementary to the substrate
Why do non competitive inhibitors reduce the rate of reaction?
Because they change the shape of the active site and so the substrate can no longer bond to the active site and form an ESC.
what is important in regulating metabolic pathways in cells?
End product inhibition
What is a metabolic pathway?
A series of reactions, all catalysed by enzymes
What type of cell division occurs in yeast?
Budding
What types of cells are found in the phloem?
- Sieve plates
- Companion cell
- Parenchyma
Discuss the ways in which genetic variation is produced, including the role of nuclear division
- Independent assortment of homologous chromosomes in metaphase 1, which allows for homologous chromosomes to have different alleles.
- Crossing over in Prophase 1, so that chromatids will have a new combination of alleles.
- Mutations, as they allow for changes in the DNA when DNA checks don’t recognise the damage.
- Fertilisation produces a large number of allele combinations as gametes aren’t genetically identical.
When does independent assortment occur in meiosis?
- Metaphase I
- Metaphase II
why does meiosis need to have twice as many stages as mitosis?
- because the chromosome number needs to be halved from 46 to 23.
- because the homologous pairs of chromosomes and sister chromatids need to be separated.
What feature of the DNA molecule is changed as a result of a mutation?
The sequence of bases
what are the effects a mutation can have on the structure and the function of a protein?
- can change the primary, secondary or tertiary structure of a protein.
- The protein could be shorter due to a deletion or longer due to an insertion.
- The protein could also remain unchanged due to a silent mutation.
- The function of the protein could either be worse or better than before.
Describe how the cells in a multicellular organism are organised
- Cells undergo differentiation and become specialised.
- A group of cells work together to form a tissue.
- A group of tissues work together to form an organ.
- A group of organs work together to form an organ system.
Why must the genetic material replicate before the division of the nucleus of the cell?
So that the daughter cells have all the identical genetic material.
What is a homologous pair of chromosomes?
- They have the same genes.
- The centromere is in the same position.
- They pair up in meiosis to form a bivalent.
What is a tissue?
A group of specialised cells working together to perform a particular function.
Whay cells are xylem made up of?
Vessel cells
What type of cells are phloem made up of?
Sieve tube elements, companion cells
How are the products of meiosis different from the peoducts of mitosis?
- In meiosis the cells produced aren’t genetically identical .
- In meiosis, haploid cells are produced ans they only contain 23 chromosomes.
- Meiosis produces gametes.
- Meiosis produces 4 cells
What happens during interphase?
- Genetic material is copied.
- DNA is checked for errors.
- Protein synthesis.
- Synthesis of more organelles.
- ATP production.
- Cell increases in size.
How is cell division in plants different to cell division in animals?
- In plants, cell plate forms between 2 new cells.
- in plants, cytokinesis starts from the middle of the cell.
- in plants, cell division only occurs in the merristem.
- no centrioles involved in the cell division of plant cells.
Describe the process of budding yeast
- Mitosis occurs.
- The cell bulges.
- The nucleus moves into the bulge
- Cytokinesis occurs and a new cell wall forms
State two other roles of mitosis in multicellular organisms.
- asexual reproduction
- growth and repair of tissues
- development of body plan
- proliferation of white blood cells
- producing gametes from haploid cells
- production of new stem cells.
Is the nucleolus visible in prophase?
No
what do opsonins do?
they bind to the antigen on a pathogen and make it easier for a phagocyte to bind.
are adult stem cells multipotent?
Yes
how thick are squamous epithelial cells?
one cell thick
2
Mitotic index = ?
Mitotic index = (the number of cells in mitosis/ the total number of cells) X 100
How does the crossing over of chromatids ensure genetic variation?
- The chromosomes of homologous pairs come together.
- In Prophase 1, the chromatids cross over.
- One chromosome from each homologous pair ends up in each cell.
- Each cell has a different chromatid and therefore a different set of alleles, which increases the genetic variation in the offspring.
How does the independent assortment of chromosomes ensure genetic variation?
- Each homologous pair of chromosomes is made up of a maternal and paternal chromosome.
- When the homologous pairs line up on the equator in Metaphase I and are separated in Anaphase I, it’s completely random which chromosome from each pair ends up in which daughter cell.
- So, the 4 daughter cells produced by meiosis have completely different combinations of those maternal and paternal chromosomes.
- This is called independent assortment (separation) of the chromosomes.
- This ‘shuffling’ of chromosomes leads to genetic variation in any potential offspring.
Where does crossing over occur in meiois?
prophase 1
Where does independent assortment occur in meiosis?
metaphase 1 and 2
do small organisms have a low or high surface area to volume ratio?
A high surface area to volume ratio
what is the surface of an insect covered with?
An exoskeleton
What is an insects exoskeleton make out of?
The polysaccharide chitin
Why do insects need spiracles on their exoskeleton?
So that gases like oxygen and carbon dioxide can diffuse into the insect
What do the spiracles lead to ?
The trachea
What are walls of the trachea in insects made up of?
Chitin
What are walls of the trachea in animals made up of?
cartilage
Why is there a short diffusion distance between the tracheoles and the insects cells?
-because tracheoles have a narrow diameter
-because tracheoles are extremely close to cells
Why does water from the tracheal fluid move into the insect cells during intense activity?
-Because during intense activity, cells around the tracheoles
undergo anaerobic respiration and this produces lactic acid.
-This lowers the water potential of the cells and causes water to move from the tracheoles into the cells by osmosis.
-This reduces the volume of the tracheal fluid, drawing air down into the tracheoles
what is a significant problem faced by insects?
Water loss
What is each spiracle surrounded by ?
A muscular sphincter
how are the gill lamellae adapted for the efficient diffusion of gases?
- they have a massive surface area for diffusion to occur
- there’s a very short diffusion distance between the walls of the lamellae and the bloodstream
- gill lamellae have an extensive network of capillaries
- The counter current exchange system
Describe the counter current exchange system
- Water and blood move in opposite directions
- Blood with a low concentration of oxygen passes into the capillaries of the gill lamellae
- As the blood passes through the gill lamellae, oxygen diffuses from the water into the blood
- Oxygenated blood passes out of the gill lamellae and leaves the gills
what is the major advantage of the counter current exchange system?
A steep concentration gradient is always maintained
Describe how bony fish maintain constant water flow through the gas exchange system
- A bony fish opens its mouth and water flows into the buccal cavity (the mouth space)
- The floor of the buccal cavity lowers and increases the volume available for water
- The fish then shuts the operculum and this increases the volume of the opercular cavity
- Due to the increased volume, the pressure in the opercular cavity falls and the floor of the buccal cavity moves upwards.
- This increases the pressure of water and so the water moves down a pressure gradient and flows over the gills in the opercular cavity.
- Now, the fish closes its mouth and opens the operculum.
- The sides of the opercular cavity squeeze inwards on the water.
- This increases the pressure of water and forces it out of the operculum
What are the 2 main adaptations of the trachea?
- The walls of the trachea contain cartilage. This prevents the walls of the trachea from collapsing when we inhale
- The trachea walls are lined with ciliated epithelia and goblet cells
what do the elastic fibres between the alveoli do during breathing?
they stretch and recoil
What happens during inhalation?
- The intercostal muscles contract
- The diaphragm contracts and flattens
- The volume of the thorax increases
- Air pressure in the lungs decreases
- Because air pressure in the lungs is now less than atmospheric pressure, air is drawn into the lungs
- Air consequently moves into the alveoli
What happens during exhalation?
- The intercostal muscles relax
- The diaphragm relaxes and becomes domed
- The volume of the thorax decreases
- Now, the air pressure in the lungs is greater than atmospheric pressure and so air is pushed out of the lungs
What is mass transport?
When molecules are carried in a transport medium, such as blood, through a circulatory system
Describe a single circulatory system
Blood only passes through the heart once in a single circuit
What’s a major problem with a single circulatory system?
Oxygen is delivered to the body cells a lot slower
Describe a double circulatory system
Blood passes through the heart twice in a single circuit. This ensures that blood moves to the body tissues rapidly and under high pressure
What is a closed circulatory system?
Where the blood is contained in blood vessels
What are the advantages of a closed circulatory system?
- The blood can move rapidly
- Oxygen can be delivered to respiring tissues quicker and carbon dioxide can be removed from the body quicker
Do insects have an open or closed circulatory system?
They have an open circulatory system
What do insects contain instead of blood?
A fluid called haemolymph
What does haemolymph carry?
Nutrients such as sugars, but not oxygen
Is the blood in the left side of the heart oxygenated or deoxygenated?
Oxygenated
Is the blood in the right side of the heart oxygenated or deoxygenated?
Deoxygenated
Describe the structure of an artery
- Very thick walls to allow the artery to withstand high pressure
- Collagen rich outer layer , which strengthens the artery wall against the pressure of the blood
- Smooth muscle layer. When this layer contracts, the diameter of the artery narrows and this allows the body to control how much blood flows to different organs
- elastic layer that is rich in elastic fibres. This allows the artery to recoil and stretch
- Lumen is lined with endothelial cells which allows for a very smooth surface and reduces friction
Describe the structure of an arteriole
-Collagen layer and the elastin layer are thinner than that of the arteries
-Thicker smooth muscle later than arteries because they control blood flow into the capillaries
Describe the structure of the capillaries
-Have a wall that is one cell thick allowing greater time for the diffusion of molecules to occur
-Capillary lumen is only slight bigger than the lumen of the red blood cells. This means that red blood cells can move slowly and in single file through the capillaries, allowing for more time for the diffusion of molecules to occur
-Capillaries have pores in their walls. These gaps allow tissue fluid to pass out of the blood. They also allow the white blood cells to leave the bloodstream
Describe the structure of veins
-Have thin walls because veins don’t have to withstand high pressure
-Large lumen to carry a great volume of blood
-Thinner elastic fibre layer because blood is under low pressure so veins don’t need to stretch and recoil
-Lumen has an internal lining of endothelial cells to create a smooth surface that reduces the friction between the blood and the wall of the vein
-Valves to ensure that there’s no backflow and that blood moves in the right direction
Describe the movement of fluid in and out of the capillary
- at the arterial end of the capillaries, hydrostatic pressure was greater than oncotic pressure, so fluid moves out of the capillary
- At the venous end of the capillary, hydrostatic pressure was lower than oncotic pressure , so fluid moves into the capillaries by osmosis
What happens to tissue fluid that isn’t reabsorbed back into the blood?
This fluid drains into lymph capillaries and becomes lymph fluid
Do lymph vessels have valves?
Yes
What adaptations do red blood cells have for transporting oxygen?
-Biconcave shape, to give a large surface area to carry the maximum amount of oxygen possible.
-Contains lots of haemoglobin.
-No nucleus to give more space for haemoglobin
How many polypeptide chains does haemoglobin have?
4
What is each of the 4 polypeptide chains in haemoglobin bound to?
A prosthetic group called haem
Which iron ion does haem contain?
Fe2+
How many molecules of oxygen can one haemoglobin molecule bind to?
1 and as oxygen is diatomic, haemoglobin binds to 8 oxygen atoms altogether
What is on the y axis of the oxygen dissociation curve?
The percentage saturation of haemoglobin with oxygen
What is on the x axis of the oxygen dissociation curve?
The partial pressure of oxygen (Kpa)
At low partial pressures of oxygen…
Haemoglobin will have a low affinity for oxygen
Why does the affinity of hemoglobin for oxygen increase after one oxygen molecule has bound?
Because as one oxygen molecule binds , the polypeptide chain opens, exposing the other 3 haem groups. The affinity of the haem groups for oxygen therefore increases
The partial pressure of oxygen is high in the lungs so..
Oxygen readily combines with haemoglobin
The partial pressure of oxygen is low in the tissues so….
Oxygen is readily released by haem
What happens when the partial pressure of carbon dioxide is high?
Haemoglobin releases oxygen more readily and it’s affinity for oxygen decreases
Is the oxygen dissociation curve shifted to the left or to the right when there’s a high partial pressure of carbon dioxide?
The right
What is the Bohr effect?
Where a high partial pressure of carbon dioxide causes haemoglobins affinity for oxygen to decrease
Describe the carriage of carbon dioxide in the blood
- The carbon dioxide produced in respiring tissues diffuses into the blood where most of it enters the red blood cells.
- In the red blood cells, the enzyme carbonic anhydrase catalyses the reaction between carbon dioxide and water.
- Carbonic acid is produced. Carbonic acid is a weak acid and so dissociate into hydrogen ions and hydrogen carbonate ions.
- The hydrogen ions can combine with haemoglobin to produce haemoglobinic acid.
- Hydrogen ions act as a pH Buffer and when haemoglobinic acid is formed, the haemoglobin is forced to drop some of the oxygen it’s carrying
- Some of the carbon dioxide that enters the red blood cells doesn’t undergo the process described above and instead combines directly with haemoglobin to form carbaminohaemoglobin
How is fetal haemoglobin different to adult haemoglobin?
Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin . This increases the oxygen transfer across the placenta from the mother to the baby
Does carbon dioxide from the foetus diffuse into the maternal blood?
Yes. This carbon dioxide lowers the oxygen affinity of the maternal haemoglobin
In which 3 ways is carbon dioxide transported around the body?
-Dissolved in the blood plasma
-Carried as carbaminohaemoglobin in red blood cells
-as hydrogen carbonate ions in the blood plasma
Do the ventricles have thicker muscular walls than the atria?
Yes
What are the atria separated from the ventricles by?
The atrioventricular valves (AV valves)
What is the left AV valve called?
What is the right AV valve called?
The tricuspid valve
What does the septum do?
It prevents any blood from passing directly between the 2 sides of the heart
What does the superior vena cava?
Brings blood from the head and other parts of the body back to the heart
What does the inferior Vena Cava do?
It brings deoxygenated blood back to the heart from lower parts of the body
why is the heart myogenic?
Because it triggers its own heartbeat- no external factors come to play
What is another name for the pacemaker?
The SAN
What is another name for the SAN?
The pacemaker
What happens when the cells in the SAN become electrically excited?
A wave of electrical excitement spreads across the atria and this causes the atria to contract
What is the contraction of the atria called?
Atria systole.
What is the AVN connected to?
Conducting fibres called Purkyne fibres
What is the Bundle of His?
Where the Purkyne fibres are bundled together
Where do the Purkyne fibres run down to ?
The apex
What happens after the AVN detects the electrical excitation passing over the atria?
The AVN then transmits the electrical excitation down to the Purkyne fibres. This electrical excitation causes the ventricles to contract
In which direction do the ventricles contract?
From the apex upwards
Why do the ventricles contract from the apex upwards?
To ensure that the maximum volume of blood is pumped out of the ventricles
Why is there a slight delay before the AVN triggers a wave of excitation down the Purkyne fibres?
To ensure that the ventricles contract after the atria have contracted
Describe the initiation and cooordinatiion of the action of the heart
1) A wave of electrical excitation spreads out from the SAN across both the atria. As a result, the atria contract and atrial systole occurs.
2) The electrical wave is stoppepd from passing through to the ventricles by the non consucting atriventricular septum.
3) The AVN picks up the electrical wave and after a short delay, sends an impulse down the bundle of His.
4) The electrical signal is down the bundle of His to the Apex. From the apex, the electrical signal branches into smaller Purkyne fibres,
5) Both ventricles contract from the ventricles upwards. This is ventricular systole.
What is the cardiac cycle?
The different steps involved in producing a single heartbeat
What does systole mean?
Contracting
What does diastole mean?
Relaxing
Describe the cardiac cycle
1) Blood flows into the atria through the vena cava and the pulmonary vein. This causes the pressure in the atria to rise.
2) At a certain point, the pressure in the atria is greater than the pressure in the ventricles.
3) This causes the Atrioventricular valves to open, allowing blood to flow down the atria and into the ventricles.
4) The atria then contract and atrial systole takes place. This pushes the remaining blood from the atria and to the ventricles
5) The ventricles then contract and enter ventricular systole. The pressure in the ventricles now rises rapidly and because the ventricular pressure is now greater than the atrial pressure, the atrioventricular valves close.
6) This prevents any blood from moving back into the atria from the ventricles
7) The semilunar valves in the aorta and pulmonary artery are also open. So blood is pumped from the ventricles and out of the heart .
8) Finally, the ventricles relax and enter ventricular diastole
9) At some point, the pressure in the ventricles falls below the pressure in the pulmonary artery and aorta. This causes the semilunar valves to shut and this prevents blood from flowing back into the ventricles.
10) The heart is now ready to enter the next cardiac cycle
What does ECG stand for?
Electrocardiogram
What does the P wave on an ECG trace show?
The contraction of the atria/ atrial systole
What does the QRS wave on an ECG trace show?
The contraction of the ventricles/ ventricular systole
What does the T wave on an ECG trace show?
the relaxation of the ventricles/ ventricular disastole
What is the heart rate?
Heart beats per minute
