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Cells Flashcards

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1
Q

What does the Modern Cell Theory state?

A

The cell is the unit of structure and function in living things.
1. All cells arise from preexisting cells
2. The cells of all living things carry out similar activities
3. Cells carry out their metabolic activities in organelles

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2
Q

What are the 2 types of cells?

A

Eukaryotic and Prokaryotic cells

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3
Q

What organelles do all cells have?

A

Cell membrane
Cytoplasm
Ribosomes

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4
Q

What organelles does a eukaryotic cell in animals also have?

A

Nucleus (and nucleolus)
Mitochondria
Golgi Apparatus
Endoplasmic Reticulum
Lysosomes
Centrioles

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5
Q

What organelles does a plant cell have?

A

The same as an animal cell but they also have:
Cell wall
Chloroplasts
Large vacuole

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6
Q

What is the function of the nucleus?

A

Controls cellular activity and contains hereditary material (DNA, in chromosomes)

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7
Q

What is the structure of the nucelus?

A

Self duplicating structure- Divides when the cell divides
Surrounded by a nuclear envelope, nucleus pores and a dense nucleolus

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8
Q

What is the structure and the function of a nuclear envelope in the nucleus?

A

A semi-permeable double membrane
Connects to endoplasmic reticulum
Controls entry and exit of substances

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9
Q

What is the structure and the function of the nuclear pores in the nucleus?

A

Approximately 3000 pores in nucleus (each 40-100nm in diameter)
Allows mRNA to leave the nucleus

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10
Q

What is the structure and the function of the nucleolus in the nucleus?

A

A small spherical organelle in the nucleoplasm.
Produces rRNA and manufactures ribosomes

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11
Q

What is the function of the mitochondria?

A

Carries out aerobic respiration (contains enzymes that make ATP)

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12
Q

What is the structure of the mitochondria?

A

•Double membrane with extensions on the inner membrane called cristae
•Jelly-like matrix contains proteins, lipids, ribosomes and trace DNA
•Found in greater numbers in active cells (such as muscle cells)

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13
Q

What is the structure of the endoplasmic reticulum?

A

Cytoplasmic, membrane-bound channels from the cell membrane to the nuclear membrane
Can be smooth (SER - no ribosomes) or rough (RER - with ribosomes)

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14
Q

What is the function of the endoplasmic reticulum?

A

SER - Synthesises, stores and transports lipids and carbohydrates
RER - Synthesises proteins and glycoproteins and provides pathway for transport throughout the cell

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15
Q

What is the structure of the golgi apparatus?

A

Stack of membranes (cristernae) with vesicles

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16
Q

What is the function of the golgi apparatus?

A

Modifies and packages proteins for export.
Glycoproteins, glycolipids, carbohydrates, secretory enzymes and lysosomes are made in the golgi apparatus

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17
Q

What is the function of ribosomes?

A

Site of protein synthesis in the cytoplasm

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18
Q

What is the structure of the ribosomes?

A

Made of a large and small subunit (each containing rRNA and protein)
May be free in cytoplasm or attached to the endoplasmic reticulum

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19
Q

What is the structure of the lysosome?

A

Up to 1ųm in diameter
Vesicle from golgi apparatus containing digestive enzymes and lysozymes (enzymes that hydrolyse bacterial cell walls)
Found in large numbers in phagocytic cells and in secretory cells such as epithelial cells

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20
Q

What is the function of the lysosome?

A

Digest bacteria ingested by phagocytic cells by breaking down material around the cell by exocytosis (releasing enzymes outside)
Breakdown old and damaged cell organelles

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21
Q

What is the function of the vacuole?

A

Provides support by making cells turgid
Act as a food store, containing coloured pigments which attract pollinating insects

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22
Q

What is the structure of the vacuole?

A

Fluid-filled sac surrounded by one membrane (tonoplast)
Plant cells have a large central vacuole which contains water, sugars, mineral salts, amino acids, pigments and waste products

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23
Q

What is the function of chloroplasts?

A

The site of photosynthesis

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24
Q

What is the structure of chloroplasts?

A

Contains chlorophyll to capture sunlight energy
Highly selective double membrane (chloroplast envelope)
Contains grana that has large surface area for attachment of chlorophyll
Has a fluid-like matrix, called stroma where sugar synthesis occurs during photosynthesis
Contains ribosomes and DNA to enable them to quickly synthesise proteins for photosynthesis

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25
Q

What is the function of the cell wall?

A

Provides mechanical strength to the plant cell (to prevent bursting from osmotic pressure)
Enables water to move through the plant

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26
Q

What is the structure of the cell wall in plant cells?

A

Composed of strong, cellulose microfibrils embedded in a matrix
Middle lamella cements neighbouring cells together

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27
Q

What are the cell walls in algae made out of?

A

Cellulose or glycoprotein (or both)

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28
Q

What are the cell walls in fungi made out of?

A

Chitin and glycan (polysaccharides), as well as glycoproteins

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29
Q

What is the structure of the cell-surface membrane?

A

‘Fluid mosaic’ phospholipid bilayer with extrinsic and intrinsic proteins embedded

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30
Q

What is the function of the cell-surface membrane?

A

Isolates cytoplasm for extracellular environment
Selectively permeable to regulate transport of substances
Involved in cell signalling/cell recognition

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31
Q

Explain the role of cholesterol in the cell-surface membrane

A

Steroid molecule connects phospholipids and reduces fluidity

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32
Q

Explain the role of glycoproteins in the cell-surface membrane

A

Cell signalling/Cell recognition (antigens) and binding cells together

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33
Q

Explain the role of glycoproteins in the cell-surface membrane

A

Cell signalling and Cell recognition

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34
Q

What is the role of plasmids in prokaryotes?

A

Small ring of DNA that carries non-essential genes
Can be exhanged between bacterial cells via conjugation

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35
Q

What is the role of flagella in prokaryotes?

A

Rotating tail propels (usually unicellular) organism
Locomotion
Sensory

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36
Q

State the role of the capsule in prokaryotes?

A

Sticks cells together
Acts as a food reserve
Protects cells from digestive enzymes (such as during phagocytosis) and external chemicals

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37
Q

Define the term eukaryotic

A

DNA is enclosed in a nucleus, contains membrane-bound specialised organelles

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38
Q

Define the term prokaryotic

A

DNA is free in cytoplasm, no membrane-bound organelles

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39
Q

What features does a bacteria cell have?

A

Murein (peptidoglycan) cell wall, slime capsule, loose (circular) DNA, plasmids, may have a flagellum

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40
Q

What is a virus and how do they work?

A

Not a living cell (acellular)
Small (20-300nm)
Don’t reproduce but replicate (inside host cells)
Attachment proteins on capsid enable virus to identify and attach to host cell

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41
Q

What is the virus life cycle?

A
  1. Recognise and attach to host cell
  2. Infect (enter) host cell
  3. Embed DNA into host cell’s DNA
  4. Force cell organelles to manufacture virus components
  5. Form new viruses
  6. New viruses exit the host cell
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42
Q

Convert to m:
mm (millimetres)
μm (micrometres)
nm (nanometres)

A

mm: 10-³ m
μm: 10-⁶ m
nm: 10-⁹ m

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43
Q

What is magnification?

A

The amount by which an object has been enlarged to view as an image
Dependent upon the lenses used

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44
Q

What is resolution?

A

The ability to distinguish between two points that lie close together
Dependent upon the wavelength of radiation used

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45
Q

How do you calculate magnification?

A

Magnification = Image size/Actual size

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46
Q

What are the 2 types of microscopes?

A

Light and Electron microscopes

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47
Q

How do light microscopes work?

A

They use a pair of convex glass lenses that can resolve images that are 0.2μm apart

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48
Q

Why can light microscope only resolve images that are 0.2μm?

A

The wavelength of light is shorter so it restricts the resolution

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49
Q

How do electron microscopes work?

A

They use a beam of electrons, that are focused by electronagnets inside a vacuum environment

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50
Q

Why is a vacuum environment needed in electron microscopes?

A

So that particles in the air don’t deflect the electrons out of the beam alignment

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51
Q

What are the two types of electron microscopes?

A

Transmission Electron Microscopes and Scanning Electron Microscopes

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52
Q

What can electron microscopes be used to look at?

A

Objects that are closer than 0.2μm apart

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53
Q

How do transmission electron microscopes work?

A

A beam of electrons passes through a thin section of a specimen
Areas that absorb the electrons appear darker on the electron micrograph that is produced

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54
Q

How do scanning electron microscopes work?

A

A beam of electrons passes across the surface and scatter
The pattern of scattering builds up a 3D image depending on the contours of the specimen

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55
Q

What are the limitations of using an electron microscope?

A

•Whole system must be in a vacuum so living specimens cant be observed
•Complex staining process required which may introduce artefacts into the image
•Specimens have to be very thin, particularly for TEM so electrons can pass through

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56
Q

What is a graticule?

A

A glass disc with an etched scale placed in the eyepiece of a microscope

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57
Q

Why is a graticule needed?

A

To mesasure size of object under objective lens

58
Q

In the cell cycle, what happens during the G1 phase?

A

•Cell is very active: Growing and carrying out metabolic functions
•Cell is preparing for next phase
•Cellular checks are made to ensure DNA is in a good enough condition to be replicated
•If DNA damaged cell division terminated at this stage

59
Q

In the cell cycle, what happens during the S phase?

A

•The cell continues to grow
•DNA is replicated
•Chromosomes are therefore duplicated

60
Q

In the cell cycle, what happens during the G2 phase?

A

•The cell continues to grow
•Organelles (such as mitochondria) are copied
•Components of microtubules (which will move chromosomes during mitosis) are synthesised

61
Q

What happens during mitosis?

A

The nucleus divides
The chromatids (containing replicated DNA) seperate from each other and are redistributed as chromosomes in the nuclei of the 2 daughter cells

62
Q

What are the stages of mitosis?

A

Interphase
Prophase
Metaphase
Anaphase
Telophase

63
Q

In mitosis, what happens during interphase?

A

The cell grows and then prepares to divide
Chromosomes and some organelles are replicated
Chromosomes also begin to condense

64
Q

In mitosis, what happens during prophase?

A
  1. Chromosomes become more visible, thicken
  2. Centrioles move to opposite ends of the cell (poles)
  3. Spindle fibres develop from each of the centrioles (spindle apparatus)
  4. Nucleolus disappears and the nuclear envelope breaks down, leaving the chromosomes free in cell cytoplasm
65
Q

In mitosis, what happens during metaphase?

A
  1. Chromosomes seen to be made up of two chromatids
  2. Microtubules attatch to centromere - chromosomes pulled to the cell equator where they line up
66
Q

In mitosis, what happens during anaphase?

A
  1. Centromeres divide, seperating each pair of sister chromatids
  2. Chromatids pulled to their respective poles as spindles contract
67
Q

When does cytokinesis occur?

A

May occur during or after mitosis
However, may not occur at all such as in muscle cells which replicate their nuclei but dont seperate to form new cells

68
Q

What happens during cytokinesis?

A

Cytoplasm divides to form 2 daughter cells, each surrounded by a plasma membrane

69
Q

What happens when the cell cycle goes wrong?

A

Uncontrolled mitosis leads to rapid cell division
Tumours form
May be benign or malignant

70
Q

How do you calculate mitotic index?

A

Number of cells undergoing mitosis ÷ Total number of cells ×100

71
Q

What is cancer?

A

Uncontrolled mitosis: Genes that control mitosis and cell cycle are faulty or damaged
Tumour (mass of cells) forms
Benign tumours (harmless) may become malignant (cancerous)

72
Q

How is cell division controlled?

A

A proto-oncogene tells a cell when to divide
A tumour suppressor gene tells cell to stop dividing
If either of the above genes are damaged then cells will divide to frequently

73
Q

How can cancer be treated?

A

Cells can be destroyed by blocking cell cycle
Chemo drugs can prevent replication of DNA or interfere with spindle formation to halt metaphase
All cells affected but cancer cells divide more rapidly and so more affected
Normal cells that divide rapidly also affected e.g hair cells by the drugs so hair loss during treatment

74
Q

Describe the process of binary fission

A

•Circular DNA (and plasmids) copied
and move towards cell membrane
•Membrane moves inwards, between the two DNA pieces, and divides the
cytoplasm
•Cell wall forms and creates two new
cells, each containing one circular
DNA strand and a variable number of plasmids

75
Q

What is diffusion?

A

The tendency of molecules to move from an area of higher concentration to an area of lower concentration
Movement down concentration gradient

76
Q

What is the equation for the rate of diffusion (Fick’s law)?

A

Rate = surface area×difference in concentration / length of diffusion path

77
Q

What factors affect the rate of diffusion (Fick’s law)?

A

Bigger surface area = faster rate
Bigger difference in concentration = faster rate
Long path = lower rate

78
Q

What is facilitated diffusion?

A

Assisted diffusion, from high to low concentration
But only at specific points along a membrane
Carrier proteins ‘help’ the process

79
Q

What is osmosis?

A

Movement of water through a membrane from higher to lower
concentration

80
Q

What is a solute?

A

Substance being dissolved in a liquid e.g salt

81
Q

What is a solvent?

A

Substance doing the dissolving (e.g water)

82
Q

What is permeability?

A

The extent to which a membrane will allow molecules to pass

83
Q

What is a semi-permeable membrane?

A

Allows some molecules to pass but not others

84
Q

Describe water potential

A

Highest water potential is 0
Pure water = 0
All other solutions have negative water potentials
More negative = more solute

85
Q

What is a hypertonic solution?

A

A solution that causes a cell to shrink
because of osmosis. Meaning water leaves the cell.

86
Q

What is a hypotonic solution?

A

A solution that causes a cell to swell
because of osmosis meaning water rushes into the cell.

87
Q

What is a isotonic solution?

A

A solution that causes no change in cell size. Meaning there is no movement of water.

88
Q

What is active transport?

A

•The movement of a substance against the concentration gradient
•Requires the cell to use energy in the form of ATP

89
Q

What is endocytosis?

A

The movement of a substance
into the cell by a vesicle. A vesicle is a form of packaging that is used by cells.

90
Q

What is exocytosis?

A

The movement of a substance out
of the cell by a vesicle

91
Q

What is phagocytosis?

A

Cytoplasm of cell surrounds and
engulfs particle (Eg. amoeba and white blood cell)

92
Q

Describe the Na/K pump

A

1.Cytoplasmic Na+ binds to the Na/K pump.
2.Na+ binding stimulates phosphorylation by ATP
3.Phosphorylation causes the protein to change its conformation, expelling Na+ to the outside.
4.Extracellular K+ binds to the protein, triggering release of the phosphate group
5. Loss of the phosphate restores the protein’s original conformation.
6.K+ is released and Na+ sites are receptive again; the cycle repeats.

93
Q

What is cell fractionation?

A

Cell fractionation is the process by which organelles can be obtained

94
Q

What are the 2 stages involved in cell fractionation?

A

Homogenation
Ultracentrifuguation

95
Q

What has to happen before cell fractionation?

A

Cells must be placed in a cold, isotonic, buffered solution:

96
Q

Why must the cell be in a cold solution before cell fractionation?

A

To prevent or reduce enzyme activity that might otherwise damage organelles

97
Q

Why must the cell be placed in an isotonic solution before cell fractionation?

A

To prevent osmosis which would cause organelles to swell, burst or shrink

98
Q

Why must the solution be buffered before cell fractionation?

A

To maintain a constant pH in order to avoid chemical damage

99
Q

Describe the process of homogenation

A

• Cells are broken up by a homogeniser (mini blender)
•Organelles are released from the cell
•Homogenate is filtered to remove debris and unbroken cells

100
Q

Describe the process of ultracentrifuguation

A

•Cell fragments are separated using an ultracentrifuge
•Homogenate is spun at varying speeds generating a centrifugal force
•Organelles are deposited into a pellet at the bottom of the tube
depending on size
•At slower speeds, heavier organelles are deposited as a pellet. E.g. Nuclei
•As speed increases, organelles of smaller sizes are deposited from the
supernatant. E.g. Chloroplasts (in plant cells) then mitochondria

101
Q

What is a pathogen?

A

A microorganism that can cause disease

102
Q

Describe the process of phagocytosis

A

1) A phagocyte recognises the antigens on a pathogen
2) The cytoplasm of the phagocyte moves round the pathogen, engulfing it.
3) The pathogen is now contained in a vacuole or a vesicle in the cytoplasm of the phagocyte.
4) A lysosome fuses with the phagocytic vacuole and the lytic enzymes break down with the pathogen
5) The phagocyte presents the pathogens antigens, it sticks the antigens on its surface to activate other immune system cells.

103
Q

What are the two types of specific response?

A

Cell mediated Immunity: T lymphocytes
Humoral immunity: B lymphocytes

104
Q

Describe cell mediated immunity (T lymphocytes)?

A

•Doesnt require antibodies
•Cells with foreign antigens on their surface are “antigen-presenting cells”
•Only responds to antigens on cell surfaces (not in body fluid)
•Antigen presenting cells can be phagocytes displaying foreign antigens, invaded body cells,
cancer cells, transplanted cells or foreign cells

105
Q

What happens during humoral immunity (B lymphocytes)

A

•Foreign cells in body fluids present antigens
•A B-lymphocyte will have a complementary antibody which
attaches to the antigen
•The antigen is taken into the B-lymphocyte, by endocytosis, and is presented on the B-lymphocytes
membrane
•TH cells bind to the antigen and stimulate B-cells to divide to form identical clones (clonal selection) which produce antibodies that are complementary to the foreign antigen
•As each B-cell produces one specific type of antibody they are called monoclonal antibodies

106
Q

What are plasma cells and how are they involved in humoral immunity?

A

Involved in the primary immune response.
•Secrete antibodies directly into body fluids
•Only survive for a few days but produce 2000 antibodies per second
•Response is slow and person will get ill before pathogen is destroyed

107
Q

What are memory cells and how are they involved in humoral immunity?

A

Involved in the secondary immune response
•Circulate in the blood and tissue fluid
•Remain in body fluids for decades
•When they encounter the antigen from the primary response they divide rapidly.
•Response is rapid and person will not get ill.

108
Q

What do antibodies do?

A

•Attach to specific antigen to form
antigen-antibody complex
• Cause bacterial cells to clump together
• Act as marker for phagocytes to bind

109
Q

What are the uses of monoclonal antibodies?

A

•Targeted medication Eg. Cancer treatment
•Medical diagnosis
•Pregnancy testing
•Transplant surgery

110
Q

How are monoclonal antibodies used for targeted medication?

A

•Direct monoclonal antibody therapy: produces monoclonal antibodies to match receptors on cancer cells. Once bound to the cancer cells, the antibodies prevent the attachment of chemical signals that cause the cells divide
• Indirect monoclonal antibody therapy: attaches cytotoxic drugs to monoclonal antibodies. Once bound to the cancer cells, cause cells to die

111
Q

How are monoclonal antibodies used for medical diagnosis?

A

Monoclonal antibodies can be used to detect the amount of certain
substances in the blood by binding to them

112
Q

How are monoclonal antibodies used in pregnancy testing?

A

•Monoclonal antibodies (and colour particles) are attached to the test strip of home pregnancy testing kits
• Pregnant women produce high levels of hCG in urine
• The hCG attaches to the antibodies and as the hCG-antibody-colour complex moves along the
testing strip they become trapped to form a coloured line

113
Q

How are monoclonal antibodies produced?

A

1.Mouse (or rabbit) exposed to antigen.
2.B cells in mouse make antibodies which are extracted.
3.B cells are mixed and fused with
cancer cells.
4.Single fused (hybrid) cells are
selected and grown.
5.All antibodies produced from each hybrid will be identical - monoclonal

114
Q

What are some ethics of monoclonal antibodies?

A

•Use of mice (or rabbits) to produce monoclonal antibodies and tumours however guidelines written to
minimise suffering
• Successful in treating cancers but caused deaths in MS sufferers however informed consent is required before treatment
• Drugs trials can potentially cause harm to healthy volunteers

115
Q

What is the ELISA test?

A

A common test used to detect is someone has been exposed to a virus such as HIV

116
Q

What are the steps taken for the ELISA test?

A

1.Virus proteins (antigens) are added
to wells of a 96-well plate
2.The antigens bind to the plastic,
coating the bottom of the wells
3.The primary antibody is added to the well.The primary antibodies (IgM) are from the patient’s serum sample.
4.Excess antibody is washed away, leaving only antibodies bound to the antigens behind. This wash removes excess antibodies that are unbound and prevents non-specific binding.
5.A secondary antibody is added to the wells. This antibody recognizes the patient IgM antibodies, bound to the antigens.The secondary antibody also has a colorimetric tag attached
6.Excess secondary antibody is washed away, leaving only secondary antibodies, bound to the patient IgM antibodies.This wash removes excess antibodies that are unbound.
7.A substrate is added to the wells.
8.Bound secondary antibody containing a colorimetric tag will cause a color change when exposed to the substrate. A color change indicates a positive reaction

117
Q

What is the structure of the virus?

A

• Lipid envelope with embedded attachment proteins
• Capsid surrounds 2 strands of RNA and enzymes (including reverse transcriptase)

118
Q

How does HIV cause AIDS?

A

•T-helper cells stimulate B cells
(to produce antibodies) or cytotoxic T-cells (to kill pathogens)
• Without the correct number of
T-helper cells, the body is unable to effectively produce an immune response and thereby becomes susceptible to disease
• Death of the patient may result
due to a disease that would not
normally affect them significantly

119
Q

How do antibiotics work?

A

•Antibiotics are only effective against bacteria: They work by disrupting the production of murein which forms bacterial cells walls
• Viruses do not have murein cell walls and they do not have organelles to replicate; viruses used host
cells and their organelles

120
Q

How is HIV replicated?

A

• HIV enters the body and circulates in blood until it binds to CD4 protein on cells (usually T-helper cells)
• Capsid fuses with cell membrane & contents are released into host cell
• Reverse transcriptase converts viral RNA to DNA which then enters the host nucleus and is embedded into the DNA
• Messenger RNA is created and provides the code for viral proteins; the host cell produces viral components and the newly formed virus breaks from the cell taking part of the membrane as it’s lipid envelope

121
Q

How do vaccines work?

A

Vaccines are a way of introducing a pathogen into the body in order to produce an immune response. The pathogen may be dead of inactivated, but the antigens on its surface will still produce an immune response. This is active immunity and results in the creation of memory B cells which will be able trigger a rapid secondary immune response should the same pathogen ever be detected again.

122
Q

What does the success of the vaccine depend on?

A

•Cost of the vaccine
•Severity of the side effects
•Ease of production, transportation and administration

123
Q

Explain some common cell adaptions

A

•Folded membrane or microvilli increase surface area e.g for diffusion
•Many mitochondria = large amounts of ATP for active transport
•Walls one cell thick to reduce distance of diffusion pathway

124
Q

Why are viruses referred to as ‘particles’ instead of cells?

A

They’re acellular and non living: no cytoplasm, cannot self-produce, no metabolism

125
Q

Describe the structure of a viral particle

A

•Linear genetic material (DNA or rNA) & viral enzymes e.g reverse transcriptase
•Surrounded by capsid
•No cytoplasm

126
Q

Describe the structure of an enveloped virus?

A

•Simple virus surrounded by matrix protein
•Matrix protein surrounded by envelope derived from cell membrane of host cell
•Attachment proteins on surface

127
Q

What are 3 ways a pathogen can damage host cells?

A

1) rupturing them to release nutrients inside them
2) breaking down nutrients inside the cell for their own use. This starves and eventually kills the cell.
3) replicating inside the cells and bursting them when they’re released

128
Q

What are the 2 ways pathogens cause disease?

A

•Production of toxins
•Cell damage

129
Q

What are the lifestyle factors that can affect the chances of getting cancer?

A

•Smoking
•Excessive exposure to sunlight
•Excessive alcohol intake

130
Q

What are the 3 surfaces of contact- where pathogens enter our body? and how do they get in?

A

•Gas-exchange system: if you breathe in air that contains pathogens, most of them will be trapped in mucus lining the lung epithelium. Some pathogens are able to reach the alveoli where they can invade cells and cause damage.
•Skin: if you damage your skin, pathogens on the surface can enter your bloodstream. Blood clots prevent pathogens from entering.
•Digestive system: if you eat or drink food that contains pathogens. Some will survive from the acidic conditions of the stomach, and invade cells of the gut wall and cause disease.

131
Q

What is cellular and humoral response?

A

•Cellular: The T-cells and other immune system cells that they interact with e.g phagocytes , form the cellular response
•Humoral: B cells and the production of antibodies form the humoral response.

132
Q

Explain what is meant by a primary response

A

•The primary response is slow because there aren’t many B-cells that can make the antibody needed to bind to it.
•The infected person will show symptoms of the disease while the body produces enough of the right antibody to overcome the infection.
•T-cells and B-cells produce memory cells. Memory T-cells remember the specific antigen and will recognise it second time round. Memory B-cells record the specific antibodies needed to bind the antigen.
•The body is now immune

133
Q

Explain what is meant by the secondary response

A

•If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response.
•Memory B-cells divide into plasma cells that produce the right antibody to the antigen. Memory T-cells divide into the correct type of T cells to kill the cell carrying the antigen.
•The secondary response often gets rid of the pathogen before you begin to show any symptoms.

134
Q

What order are the organelles separated into in ultracentrifugation?

A
  1. Nuclei
  2. Mitochondria
  3. Lysosome
  4. Endoplasmic reticulum
  5. Ribosomes
135
Q

Define virus

A

Acellular, non-living particles
Smaller than bacteria

136
Q

How do vaccines protect individuals and populations against disease?

A

Vaccines contain antigens that cause your body to produce memory cells against a particular pathogen, without the pathogen causing disease. This means you become immune without getting the symptoms.
Vaccines protect individuals because they reduce the occurance of the disease. Those not vaccinated are less likely to catch the diease because there are fewer people to catch it from - this is called herd immunity.

137
Q

What is the role of phospholipids in cell-surface membrane structure?

A

Their hydrophilic/hydrophobic interactions lead to the formation of a phospholipid bilayer.

  1. Allow lipid-soluble substances to enter/exit cell.
  2. Prevent water-soluble substances entering and leaving cell.
  3. Make the membrane flexible and self-sealing.
138
Q

What is the role of proteins in cell-surface membrane structure?

A

Some in surface of bilayer:
1. Act to provide mechanical support to membrane.
2. Along with glycolipids, act as cell receptors for molecules such as hormones.
Some span the entire membrane:
3. Protein channels - water filled tubes allowing water-soluble ions to diffuse across the membrane.
4. Protein carriers - bind to ions or molecules like glucose/amino acids - then change shape to move these molecules across the membrane.
5. Help cells adhere together.
6. Form cell-surface receptors for identifying cells.

139
Q

What is the role of cholesterol in cell-surface membrane structure?

A
  1. Reduce lateral movement of other molecules (including phospholipids) - pulls together the fatty acid tails, limiting movement without making the membrane too rigid.
  2. Make the membrane less fluid at high temperatures.
  3. Prevent leakage of water and dissolved ions from the cell, as cholesterol molecules are very hydrophobic.
140
Q

Explain the “fluid-mosaic” model of the cell-surface membrane structure

A

The arangement of all the various molecules combined into the structure.
●Fluid: Membrane is flexible and can constantly change in shape as individual phospholipid molecules can move relative to one another.
●Mosaic: Proteins embedded in the phospholipid bilayer vary in shape, size + pattern like tiles in a mosaic.

A Level Biology (7 decks)

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