5 Markers Flashcards
describe the structure of protein [5]
protein is a polymer of amino acids
joined by peptide bonds
formed by condensation
primary structure is type, order and number of amino acids
secondary structure is folding of polypeptide chain due to hydrogen bonding
tertiary structure is 3d folding due to disulphide bridges and ionic bonds
quaternary structure is 2 or more polypeptide chains usually with prosthetic group
describe the structure of starch [5]
helical shape SO compact
Insoluble SO osmotically inactive
Large molecule SO cannot leave cell
describe the structure of cellulose [5]
long straight chains of B-glucose
joined by hydrogen bonding
to form micro fibrils
which provides rigidity
Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells. (5)
- Cell homogenisation to break open cells;
- Filter to remove (large) debris/whole cells;
- Use isotonic solution to prevent damage to mitochondria/organelles;
- Keep cold to prevent/reduce damage by enzymes / use buffer to prevent protein/enzyme denaturation;
- Centrifuge (at lower speed/1000 g) to separate nuclei/cell fragments/ heavy organelles;
- Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom;
describe how the induced fit model explains how enzymes lower activation energy
-tertiary structure of enzymes means
-shape of active site is complementary to substrate
-active site changes shape as it binds to substrate
-due to interactions between R-groups
-putting mechanical pressure on bonds
-stressing bonds lowers activation energy
Describe the stages of Mitosis
Prophase: chromosomes coil, nuclear envelope and nucleolus breaks down, spindle starts to form
Metaphase: chromosomes align at equator of cell (perpendicular to axis of spindle), spindle attach to centromere.
Anaphase: spindles shorten pulling centromere to poles, chromatids separated into two daughter chromosomes
Telophase: chromosomes lengthen, nuclear envelope and nucleolus reappear.
describe the structure of DNA
polymer of nucleotides
formed from deoxyribose, phosphate and nitrogenous base
joined by phosphodiester bonds
coiled in a double helix held by hydrogen bonds
between adenine thymine cytosine guanine
Many different substances enter and leave a cell by crossing its cell surface membrane. Describe how substances can cross a cell surface membrane. (5)
1 (Simple / facilitated) diffusion from high to low
concentration / down concentration gradient;
2 Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer;
OR
Large / polar / water-soluble molecules go through proteins;
3 Water moves by osmosis / from high water potential to low water potential / from less to more negative water potential;
4 Active transport is movement from low to high
concentration / against concentration gradient;
5 Active transport / facilitated diffusion involves proteins/carriers;
6 Active transport requires energy / ATP;
7 Ref. to Na+ / glucose co-transport;
describe semi conservative replication of DNA [5]
-Helicase unzips double helix by breaking hydrogen bonds between nitrogenous bases
-Free nucleotides activated by ATP. they are then attracted to exposed nucleotides
-They join & form hydrogen bonds with their pair
-Then DNA polymerase (5’-3’) moves over each nucleotide and joins adjacent ones via condensation reaction. Forming phosphodiester bonds
-Each DNA molecules consists of one original and one new strand
Explain the role of B-lymphocytes and T-lymphocytes in the defence of the body against a virus infection. [5]
1.B lymphocytes produce antibodies/involved in humoral response;
2.T lymphocytes involved in cell mediated immunity;
3.Macrophages present antigens;
4.(specific) B lymphocytes recognise/bind to antigen;
5.increase in numbers by mitosis;
6.produce plasma cells (which make antibodies);
7.antibodies bind to and clump/ agglutinate virus;
8.memory cells produced by 1st exposure/cloned on 2nd exposure;
9.T lymphocytes(helpers) produce 10.lymphokines/chemicals;
11.which aid B lymphocyte cloning;
12.encourages phagocytes to engulf clumped virus;
13.killer T cells kill virus infected cells;
Describe the structure of a cell membrane. (5)
- Double layer of phospholipid molecules;
- Detail of arrangement of phospholipids;
- Intrinsic proteins/protein molecules passing right through;
- Some with channels/pores;
- Extrinsic proteins/proteins only in one layer/on surface;
- Molecules can move in membrane/dynamic/membrane contains cholesterol;
- Glycocalyx/carbohydrates attached to lipids/proteins;
how do monoclonal antibodies work in pregnancy tests
how do you not know this, Luke. come on mate. This is easy. search up a diagram of it. You’re doing well! keep revising
Describe the part played by cell surface membranes in regulating the movement of substances into and out of cells. (6)
- Non-polar/lipid soluble molecules move through phospholipid layer/bilayer;
- Small molecules/water/gases move through phospholipid layer/bilayer;
- Ions/water soluble substances move through channels in proteins;
- Some proteins are gated;
- Reference to diffusion;
- Carriers identified as proteins;
- Carriers associated with facilitated diffusion;
- Carriers associated with active transport/transport with ATP/pumps;
- Different cells have different proteins;
- Correct reference to cytosis;
Explain how amino acid molecules may be linked to form a polypeptide chain which is folded into a specific tertiary shape. (6)
- Condensation;
- removal of water molecule;
- from amino and carboxyl groups;
- forming peptide bonds;
- same amino acids in same sequence;
- bonds form between R-groups/side chains;
- e.g. sulphur-containing amino acids / ionic bonds / hydrogen bonds;
- bonds form in same place;
Describe how molecular shape is important in explaining the way in which enzymes may be affected by inhibitors. (6)
1 Active site (of enzyme) has particular shape;
2 (Into which) substrate molecule fits / binds;
3 Appropriate reference linking induced fit and shape;
4 (Competitive inhibitor) has similar shape to substrate;
5 Also fits active sites;
6 Prevents substrate access;
7 (Non-competitive inhibitor) fits at site other than active site;
8 Distorting shape of active site / enzyme;
6 Prevents substrate access; (award once only)
9 Two types identified as competitive and non-competitive;
The bacteria in the intestine are prokaryotic cells. The epithelial cells which line the small intestine are eukaryotic cells. Describe the ways in which prokaryotic cells and eukaryotic cells differ. (6)
1 Prokaryotic cells do not have a nucleus / have genetic material
in cytoplasm;
2 DNA in loop / ring;
3 Not associated with proteins / do not have chromosomes /
chromatin / do not divide by mitosis;
4 Smaller ribosomes;
5 No membrane-bound organelles;
6 Such as mitochondria / lysosomes / endoplasmic reticulum /
Golgi / chloroplasts;
7 Prokaryotic cells may have mesosomes;
8 Prokaryotic cells smaller;
9 May be enclosed by capsule;
Glucose is absorbed from the lumen of the small intestine into epithelial cells. Explain how the transport of sodium ions is involved in the absorption of glucose by epithelial cells. (5)
- Na+ ions leave epithelial cell and enter blood;
- (Transport out is by) active transport / pump / via carrier protein using ATP;
- So, Na+ conc. in cell is lower than in lumen (of gut);
- Sodium/Na+ ions enter by facilitated diffusion;
- Glucose absorbed with Na+ ions against their concentration/diffusion gradient / glucose absorbed down an electrochemical gradient;
Use your knowledge of protein structure to explain why enzymes are specific and may be affected by non-competitive inhibitors. (5)
1 each enzyme / protein has specific primary structure / amino acid sequence;
2 folds in a particular way / has particular tertiary structure giving an active site with a unique structure;
3 shape of active site complementary to / will only fit that of substrate; maximum of three marks for inhibition, points 5 - 8
4 inhibitor fits at site on the enzyme other than active site;
5 distorts active site;
6 so substrate will no longer fit / form enzyme-substrate complex
Describe the role of the enzymes of the digestive system in the complete breakdown of starch. (5)
Amylase;
(Starch) to maltose:
Maltase;
Maltose to glucose;
Hydrolysis;
(Of) glycosidic bond;
Describe the processes involved in the absorption of the products of starch digestion. (5)
Glucose moves in with sodium (into epithelial cell);
Via (carrier / channel) protein / symport;
Sodium removed (from epithelial cell) by active transport / sodium- potassium pump;
Into blood;
Maintaining low concentration of sodium (in epithelial cell) / maintaining sodium
concentration gradient (between lumen and epithelial cell);
Glucose moves into blood;
By (facilitated) diffusion;
In humans, the enzyme maltase breaks down maltose to glucose. This takes place at normal body temperature.
Explain why maltase:
-only breaks down maltose
-allows this reaction to take place at normal body temperature. (5)
- Tertiary structure / 3D shape of enzyme (means);
- Active site complementary to maltose / substrate / maltose fits into active site / active site and substrate fit like a lock and key;
- Description of induced fit;
- Enzyme is a catalyst;
- Lowers activation energy / energy required for reaction;
- By forming enzyme-substrate complex;
Explain how the structure of DNA is related to its functions. (6)
- Sugar-phosphate (backbone)/double
stranded/helix so provides strength/stability
/protects bases/protects hydrogen bonds; - Long/large molecule so can store lots of
information; - Helix/coiled so compact;
- Base sequence allows information to be
stored/ base sequence codes for amino
acids/protein; - Double stranded so replication can occur
semi-conservatively/ strands can act as
templates; - Complementary base pairing / A-T and G-C
so accurate replication/identical copies can
be made; - (Weak) hydrogen bonds for replication/
unzipping/strand separation; - Many hydrogen bonds so stable/strong;
