2) Cells Flashcards
1
Q
Eukaryotic (eg human) cells
compared with Prokaryotic
(bacterium)
A
- Bacterial cell is much smaller than a human cell; (or human cell is much larger than a bacterial 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
- Bacterial DNA is circular but human DNA is linear
- Bacterial DNA is ‘naked’ whereas human DNA is bound to histones/proteins;
2
Q
How to measure
objects using an eyepiece graticule
A
- Use eyepiece graticule to measure the object e.g. nucleus or capillary
- Calibrate eyepiece graticule against stage micrometer
- Take a number of measurements and calculate the mean
3
Q
Advantages and
Limitations of Transmission Electron
Microscope
A
Advantages -
- Small objects can be seen;
- TEM has high resolution as wavelength of electrons shorter;
Limitations -
- Cannot look at living cells as cells must be in a vacuum;
- Must be thin specimen;
- Preparation may create artefact;
- Does not produce colour image;
4
Q
Comparison of TEM
and optical microscope
A
- TEM use electrons and optical use light;
- TEM allows a greater resolution;
- (So with TEM) smaller 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;
5
Q
Advantage of
electron microscope over optical
microscope
A
- High resolution;
- Can see internal structure of organelles
6
Q
Conditions required for cell homogenisation
A
- Ice-cold – Slows/stops enzyme activity to prevent digestion of organelles/mitochondria;
- Buffered – Maintains pH so that enzymes/proteins are not denatured;
- Same water potential – Prevents osmosis so no lysis/shrinkage of organelles/mitochondria;
7
Q
How is mitochondria separated
A
- Break open cells/homogenise/produce homogenate;
- Remove unbroken cells/larger debris by filtration;
- Centrifuge highest density organelle nuclei obtained as pellet at slowest speed
- Mitochondria in 2nd pellet as less dense than nucleus/organelle in first pellet;
8
Q
Stages of mitosis - chromosome behavior in each stage ?
A
Prophase - chromosomes become visible, appear as two sister chromatids joined at centromere
Metaphase - chromosomes line up on the equator, chromosomes attached to spindle fibers by their centromere
Anaphase - centromere splits, sister chromatids pulled to opposite ends of the cell.
Telophase - chromatids unwind an become longer.
9
Q
How does bacteria replicate
A
- Replication of (circular) DNA;
- Division of cytoplasm to form 2 daughter cells
- Each with a single copy of (circular) DNA;
10
Q
Mitosis practical - preparing root tip squash techniques
A
1.Push hard – spread/squash tissue;
2 Not push sideways – avoid rolling cells together/breaking chromosomes;
11
Q
Mitosis Practical – How do we
identify anaphase?
A
- Chromosomes/chromatids are (in two groups) at poles of spindle/at ends of spindle;
- V-shape shows that (sister) chromatids have been pulled apart at their centromeres
12
Q
Describe all types of membrane
transports
A
- (Simple / facilitated) diffusion from high to low concentration / down concentration gradient;
- Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer; OR Large / polar / water-soluble
- molecules go through proteins;
- Water moves by osmosis / from high water potential to low water potential / from less to more negative water potential;
- Active transport is movement from low to high concentration / against concentration gradient. Active transport/ facilitated diffusion involves proteins/carriers;
- Active transport requires energy / ATP;
- Ref. to Na+ / glucose co-transport;
13
Q
Active Transport – mitochondria
A
- Mitochondria site of respiration;
- Release energy / produce ATP; (Reject make energy in context of this point)
- Energy / ATP necessary for active transport;
- To move substances against concentration gradient;
14
Q
Active Transport compared with
facilitated diffusion
A
- Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins;
- Facilitated diffusion does not use ATP / is passive whereas active transport uses ATP;
- Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient
15
Q
Disruption to respiration to co-
transport of glucose from ileum to
the blood
A
- Less ATP / no ATP
- For active transport
- So sodium ions cannot be pumped into blood
- Sodium ion concentration in cell becomes too high
- Can’t maintain a concentration gradient for sodium ions so sodium ions cannot diffuse into cells
- So glucose cannot be taken into cells from lumen
16
Q
Why does inhibiting
respiration/using cyanide prevent
active transport?
A
- Oxygen is required for aerobic respiration which releases ATP
- ATP is needed to change the shape of the protein carrier
- Which would cause the release of the transported ion/molecule
- So no ATP, no Active Transport
17
Q
How do we find water potential of
plant tissue practically
A
- Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis;
- Find concentration where curve crosses the x-axis/where percentage change is zero;
- Use (another) resource to find water potential of sucrose concentration (where curve crosses x-axis);
18
Q
What is antigen?
A
- foreign protein which stimulates an immune response - produces antibodies
19
Q
What is antibody
A
- a protein which is specific to an antigen
- produced by B cells or secreted by plasma cells.
20
Q
Antibody specificity
A
- Antibody has (specific) tertiary structure
- Has binding site/ variable region which only binds to one antigen
- Antigen is only found on this particular (pathogen/cell/tissue)
- so antibody (only) binds to / forms antigen/antibody complex with these (pathogen/cell/tissue) destroying them
21
Q
What is a monoclonal antibody
A
- Antibody specific/complementary to one antigen only
- Antibodies all the same and from one original plasma cell
- Derived from a hybridoma cell/fused B lymphocyte and cancer cell
22
Q
What is phagocytosis
A
- Phagosome/vesicle fuses with lysosome;
- (pathogen) destroyed by lysozymes/hydrolytic enzymes;
- Antigen (from pathogen) displayed on cell membrane (of phagocyte/antigen presenting cell);
23
Q
HIV treatment with anti-retroviral
drug AZT
A
- Person (infected with HIV) has HIV DNA (in their DNA);
- New HIV (particles) still made;
- (AZT) inhibits reverse transcriptase;
- (AZT) stops replication of HIV;
- Stops destruction of more / newly infected T cells;
- So immune system continues to work (and AIDS does not develop);
24
Q
Immunity – Compare Active and
Passive Immunity
A
- 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;
25
Q
Antigen-Antibody
complex formation
A
- Antibody has 4 polypeptide chains and has a quaternary structure
- Antibody has a variable region which has a specific amino acid sequence/primary structure
- Shape of the binding site is complementary to the antigen
- Forming an antigen-antibody comple
26
Q
Compare Primary and
Secondary Response
A
- Before vaccination no antibody released because patients not yet encountered vaccine/antigen/virus;
- Primary response/after first dose) activation/clonal selection/expansion of B cells into plasma cells;
- Plasma cells release antibodies;
- Secondary response/after second dose) memory cells produce more antibodies/produce antibodies more
quickly;
27
Q
How a vaccine
produces an immune response
A
- Vaccine contains antigen from pathogen;
- Macrophage presents antigen on its surface;
- T cell with complementary receptor protein binds to antigen;
- T cell stimulates B cell;
- (With) complementary antibody on its surface;
- B cell/plasma cell secretes large amounts of antibody;
- B cell divides to form clone all secreting/producing same antibody;
28
Q
Humoral Response
A
- Antigen on surface of bacterium binds to surface protein / surface receptor on a (specific/single) B cell;
- (Activated) B cell divides by mitosis / produces clone;
- (Division) stimulated by cytokines / by T cells;
- B cells/plasma cells release antibodies;
- (Some) B cells become memory cells;
- Memory cells produce plasma / antibodies faster;
29
Q
Monoclonal Antibody
A
- Antibody specific/complementary to one antigen only
- Antibodies all the same/one type only/ from one original plasma cell
- Derived from a hybridoma cell/fused B lymphocyte and cancer cell
