topic 2 Flashcards
Prokaryote and
animal cell
comparison
- Bacterial cell is much smaller than a human cell;
- Bacterial cell has a cell wall but human cell does not;
- Bacterial cell lacks a nucleus but human cell has a nucleus;
- Bacterial cell lacks membrane-bound organelles but human cell has membrane-bound organelles;
- Bacterial ribosomes smaller than human ribosomes / bacteria have
70S ribosomes whereas humans have 80S ribosomes; - Bacterial DNA is circular but human DNA is linear;
- Bacterial DNA is ‘naked’ whereas human DNA is bound to histones / proteins
Phospholipid arrangement in a
membrane
- Bilayer OR Water is present inside and outside a cell;
- Hydrophobic (fatty acid) tails point away/are repelled from water
OR
Hydrophilic (phosphate) heads point to/are in/are attracted to water;
Hydrophobic
substances moving
across membranes
- Lipid soluble;
- (Diffuse through) phospholipid (bilayer);
Role of organelles and
proteins
- DNA in nucleus is code (for protein);
- Ribosomes/rough endoplasmic reticulum produce (protein);
Accept rER for ‘rough endoplasmic reticulum’ - Mitochondria produce ATP (for protein synthesis);
- Golgi apparatus package/modify;
OR
Carbohydrate added/glycoprotein produced by Golgi apparatus;
Accept body for ‘apparatus’ - Vesicles transport
OR
Rough endoplasmic reticulum transports; - (Vesicles) fuse with cell(-surface) membrane;
Describe how you
would use cell
fractionation
techniques to obtain a
sample of
mitochondria from
leaf tissue.
- Macerate / homogenise / blend / break tissues / cells (in solution);
- Centrifuge the supernatent;
- At different / increasing speeds until mitochondria fraction obtained/until 3 rd pellet is obtained;
Explain the conditions
that would be
necessary for cell
fractionation.
- Ice-cold - Slows / stops enzyme activity to prevent digestion of
organelles / mitochondria; - Buffer - Maintains pH so that enzymes / proteins are not denatured;
Reject reference to cells - Same water potential - Prevents osmosis so no lysis / shrinkage of organelles / mitochondria;
Explain how
ultracentrifugation
separates different
molecules.
- Spin (liquid / supernatant) at (very) high speed / high g;
Need context of high, not just ‘faster’, ‘higher’ in context of use of bench centrifuge - Molecules separate depending on (molecular) mass / size / density;
Why is a detergent
used to lyse (breaking
open) cells and
organelles.
- Cell membranes made from phospholipid;
- (Detergent) dissolves membranes / phospholipid (bilayer);
Ignore breaks down
Reject hydrolysis
TEM compared to
optical microscope
- TEM use electrons and optical use light;
- TEM allows a greater resolution;
- (So with TEM) smaller organelles / named cell structure can be
observed
OR
greater detail in organelles / named cell structure can be observed; - TEM view only dead / dehydrated specimens and optical (can) view
live specimens; - TEM does not show colour and optical (can);
- TEM requires thinner specimens;
- TEM requires a more complex/time consuming preparation;
- TEM focuses using magnets and optical uses (glass) lenses
TEM compared to
SEM
Higher resolution OR View internal structures
Why must a sample
for a microscope be
thin?
- Need a single layer of cells / only a few cells thick / not too many layers / detail obscured by cells underneath;
- Light must be able to pass through;
Making a temporary
mount (microscope
slide)
- Add drop of water to (glass) slide;
- Obtain thin section (of plant tissue) and place on slide / float on drop of water;
- Stain if necessary;
- Lower cover slip using mounted needle.
Measuring dry mass
- Heat at 100°C / heat to temp to evaporate water;
Value which would not burn material - Weigh and heat until no further change in mass;
Mitosis
(During prophase)
1. Chromosomes coil / condense / shorten / become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the centromere;
(During metaphase)
3. Chromosomes line up on the equator / centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;
(During anaphase)
6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles /
ends of the cell / separate;
(During telophase)
8. Chromatids / chromosomes uncoil / unwind / become longer
Mitosis - root tip
experiment
Why the tip?
Pressed down firmly
on the cover slip?
Ensuring accuracy
Where dividing cells are found / mitosis occurs
Single / thin layer of cells / spread out cells so light passes through
1. Examine large number of fields of view / many cells;
2. To ensure representative sample;
OR
3. Repeat count;
4. To ensure figures are correct;
OR
5. Method to deal with part cells shown at edge /count only whole cells;
6. To standardise counting
Cytokinesis
The division of the cytoplasm
Explain how bacterial
cells divide
- Binary fission;
- Replication of (circular) DNA;
- Replication of plasmids
- Division of cytoplasm to produce 2 daughter cells;
- Each with single copy of (circular) DNA;
Transport across
membranes (parts of membrane)
- Phospholipid (bilayer) allows movement/diffusion of nonpolar/lipid-soluble substances;
- Phospholipid (bilayer) prevents movement/diffusion of polar/charged/lipid-insoluble substances OR (Membrane) proteins allow
polar/charged substances to cross the membrane/bilayer; - Carrierproteins allow active transport;
- Channel/carrier proteins allow facilitated diffusion/co-transport;
- Shape/charge of channel / carrier determines which substances move;
- Number of channels/carriers determines how much movement;
- Membrane surface area determines how much diffusion/movement;
- Cholesterol affects fluidity/rigidity/permeability;
Facilitated diffusion
- Carrier / channel protein;
- (Protein) specific / complementary to substance;
- Substance moves down concentration gradient
Diffusion and osmosis
similarities
- (Movement) down a gradient / from high concentration to low concentration;
- Passive / not active processes;
OR
Do not use energy from respiration / from ATP / from metabolism;
Co-transport of
glucose
- Sodium ions actively transported from ileum cell to blood;
- Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);
- Glucose enters by facilitated diffusion with sodium ions;
ATP hydrolase and
active transport
- (ATP to ADP + Pi ) Releases energy;
- (energy) allows ions to be moved against a concentration gradient
OR
(energy) allows active transport of ions;
Osmosis - tissue in
more concentrated
solution
- Water potential of solution is less than / more negative than that of potato tissue;
Allow Ψ as equivalent to water potential - Tissue loses water by osmosis.
Membrane
adaptations for
absorption
- Membrane folded so increased / large surface area;
OR
Membrane has increased / large surface area for (fast) diffusion / facilitated diffusion / active transport / co-transport; - Large number of protein channels / carriers (in
membrane) for facilitated diffusion; - Large number of protein carriers (in membrane) for active
transport; - Large number of protein (channels / carriers in membrane) for co-transport
What is a monoclonal
antibody?
(Antibodies with the) same tertiary structure;
OR
(Antibody produced from) identical/cloned plasma cells/B cells/B lymphocytes;
Cells that stimulate an
immune response
- (Cells from) other organisms/transplants;
- Abnormal/cancer/tumour (cells);
- (Cells) infected by virus
- Pathogens
What is an antigen?
- Protein;
- Found on a cell surface membrane/pathogen surface
- (that) stimulates an immune response / production of antibody;
What is an antibody?
- A protein / immunoglobulin specific to an antigen;
- Produced by B cells
OR
Secreted by plasma cells
Antibody specificity
- Each protein has a different tertiary structure;
- (Each) antibody has a specific antigen / binding / variable region / site;
- So, (each antibody) forms different antigen-antibody complex
OR
(each antibody) only binds to complementary (protein);
Phagocytosis
- Phagocyte engulfs to form vacuole / vesicle / phagosome;
- Lysosome fuses and empties contents into vacuole / vesicle / phagosome;
- (Releasing) enzymes that digest / hydrolyse bacteria;
Role of the disulphide
bridge in antibody
structure
Joins two (different) polypeptides;
Production of
antibodies
- Helper T cell / TH cell binds to the antigen (on the antigen-presenting cell / phagocyte);
- This helper T / TH cell stimulates a specific B cell;
- B cell clones
OR
B cell divides by mitosis; - (Forms) plasma cells that release antibodies;
Vaccination
- Antigen on surface of pathogen binds to surface receptor on a (specific / single) B cell.
- (Activated) B cell divides by mitosis;
- (Division) stimulated by T cells;
- B cells release antibodies;
- (Some) B cells become memory cells;
- Memory cells produce antibodies faster
Active v passive
immunity
- Active involves memory cells, passive does not;
- Active involves production of antibody by plasma cells / memory cells;
- Passive involves antibody introduced into body from outside / named source;
- Active long term, because antibody produced in response to antigen;
- Passive short term, because antibody (given) is broken down;
- Active (can) take time to develop / work, passive fast acting
ELISA test
- (First) antibody binds/attaches /complementary (in shape) to antigen;
- (Second) antibody with enzyme attached is added;
- (Second) antibody attaches to antigen;
Accept (second) antibody attaches to (first) antibody (indirect ELISA test). - (Substrate/solution added) and colour changes;
Only award if enzyme mentioned
viral replication
- virus attaches to surface of host cell
- virus injects viral DNA/RNA into host cell
- viral DNA/RNA replicates and produces new viral proteins
- new viral particles are formed
- host cell bursts, releasing viral particles
mitotic index equation
number of cells in mitosis / total number of cells
