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A Level Biology AQA > 2. Cells > Flashcards

2. Cells Flashcards

1
Q

What is a Eukaryotic cell ?

A

A cell that has a distinct nucleus and possesses membrane-bound organelles

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2
Q

What is the function of the nucleus?

A
  • Control centre of the cell, through the production of mRNA and tRNA
  • Contains the genetic material of the cell in the form of DNA and chromosomes
  • Manufacture RNA
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3
Q

What is the nuclear envelope?

A

-A double membrane surrounding the nucleus
-Outer membrane is continuous with the Endoplasmic Reticulum of the cell and will often have ribosomes on its surface

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4
Q

What is the function of the nuclear envelope?

A

-Controls the entry and exit of materials
- Contains reactions taking place within it

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5
Q

What are the function of the Nuclear Pores?

A

Allows passage of large molecules such as messenger RNA, out of the nucleus.

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6
Q

What is Nucleoplasm

A

Granular, jelly-like material that makes up the bulk of the nucleus

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7
Q

What is the nucleolus?

A

Small spherical region within the nucleoplasm
There may be multiple in the nucleus

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8
Q

What is the function of the nucleolus?

A

Manufactures ribosomal RNA and assembles ribosomes

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9
Q

Describe the structure of a chromosome

A

Consists of protein-bound, linear DNA
Chromatin is the material that makes up chromosomes

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10
Q

What is the function of the mitochondria

A

Site of Aerobic Respiration
Responsible for the production of the energy-carrier molecule ATP

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11
Q

What is the function of the double membrane of a mitochondrion?

A

Controls entry and exit of material
The inner membrane is folded to form extensions called Cristae

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12
Q

What is the function of the Cristae?

A

Provide large surface area for attachment of enzymes and other proteins required in respiration

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13
Q

What is the function of the matrix within the mitochondrion?

A

It contains proteins, lipids, ribosomes and DNA and controls the production of some of the mitochondrion proteins.
It is also the location of many enzymes involved in respiration

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14
Q

Describe the structure of the Endoplasmic Reticulum

A

3D system of sheet-like membranes spread throughout the cytoplasm
Continuous with outer membrane of nucleus
Membranes enclose a network of tubules and flattened sacs called cisternae

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15
Q

What is the function of the Rough Endoplasmic Reticulum?

A

Provide a large surface area for the synthesis of proteins and glycoproteins
Provide a pathway for transport of proteins throughout the cell

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16
Q

Describe the difference in structure between the rough Endoplasmic Reticulum and the smooth Endoplasmic reticulum

A

RER has ribosomes on the outer surface of membranes and SER lacks ribosomes on its surface and is often more tubular in appearance.

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17
Q

What is the function of the Smooth Endoplasmic Reticulum?

A

Synthesis, store and transport of lipids and carbohydrates

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18
Q

Describe the structure of a ribosome

A

Small cytoplasmic granules found in all cells, either in cytoplasm or in RER

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19
Q

What are the 2 types of ribosomes and what are the differences between the 2?

A

80s- found in eukaryotic cells
70s- found in prokaryotic cells & mitochondria. Also slightly smaller

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20
Q

Describe the structure of the Golgi Apparatus

A

Similar to SER but more compact
Stacks of membranes that make up flattened sacs called cisternae, with small rounded hollow structures called vesicles

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21
Q

What happens in the Golgi Apparatus

A

Proteins and lipids produced in ER are passed to Golgi where it modifies them
The modified proteins are transported to the vesicles where they are regularly pinched off the ends of the cisternae. These vesicles move to the cell surface, fuse with the membrane and release their content outside the cell
(PACKAGING AND PROCESSING)

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22
Q

What are the functions of the Golgi Apparatus

A

Add carbohydrates to proteins to form glycoproteins
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
Form lysosomes

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23
Q

What are lysosomes

A

Formed when vesicles produced by Golgi Apparatus contain enzymes
They isolate enzymes from the rest of the cell before releasing them outside the cell or into phagocytise vesicles within the cell

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24
Q

What are the functions of the lysosomes

A

Hydrolysed material ingested by phagocytic cells
Exocytosis
Digest worn out organelles
Completely break down cells after they die (autolysis)

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25
Q

What is the function of the chloroplast

A

Site of photosynthesis

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26
Q

Describe the structure and function of the chloroplast envelope

A

Double plasma membrane
Highly selective in what leaves and enters

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27
Q

Describe the structure and function of the Grana

A

Structure: stacks of 100 disc-like structures called thylakoids
Function: location of first stage of photosynthesis - absorbs light

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28
Q

What are thylakoids?

A

Contain photosynthetic pigment - chlorophyll
Some have tubular extensions (lamella) which join ajecent grana.

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29
Q

Describe the structure and function of the Stroma

A

Structure: fluid filled matrix, within it are other structures such as Starch grains
Function: location of the seconds stage of photosynthesis (synthesis of sugars)

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30
Q

How is the chloroplast adapted?

A

Granal membranes provide large surface area for attachment of chlorophyll, electron carriers and enzymes required in the first stage of photosynthesis
Fluid in the stroma possesses all the enzymes need to make sugars in the 2nd stage
Chloroplasts contain both DNA and ribosomes to manufacture proteins for photosynthesis

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31
Q

What is the function of the cell wall

A

Provided mechanical strength to prevent cell from bursting due to pressure created by osmosis
Allows water to move throughout the cell

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32
Q

What is the function of the vacuole

A

Temporary food store
Support for plants by making them turgid

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33
Q

Describe the structure and function of circular DNA

A

Structure: DNA is free in the cytoplasm
Function: Possess the genetic information for the replication of bacterial cells

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34
Q

Describe the structure and function of plasmids

A

Structure: separate from circular DNA, smaller pieces of DNA that can reproduce independently
Function: possess genes that may aid in the survival of bacteria in adverse conditions, can be used as vectors between bacteria

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35
Q

Which ribosomes are present in prokaryotic cells?

A

70s (slightly smaller)

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36
Q

What is the function of the flagella

A

Rotates to move the cell

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37
Q

Describe the structure and function of the cell wall of a prokaryotic cell

A

Made up of MUREIN
Functions to give strength and structure, protects against mechanical damage and osmotic lysis

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38
Q

Describe the structure & function of the capsule

A

Structure: A layer of slime around the cell wall
Function: Protects the bacterium from other cells and helps groups of bacteria stick together for further protection

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39
Q

What are the features of an optical (light) microscope

A

Optical uses beam of light to produce an image
Magnifies up to x2000
Lower resolution
Cheap & easy to use
Creates only 2D images

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40
Q

What are the features of an electron microscope

A

Uses beam of electrons focused by electromagnets to produce an image
Magnifies up to x2,000,000
Higher resolution
Extremely expensive and more difficult to keep
Creates both 2D and 3D images

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41
Q

Why does an optical (light) microscope have a lower resolution than an electron microscope

A

Wavelength of light is a lot longer
Can only distinguish between 2 objects if they are 0.2 μm or further apart

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42
Q

Why does an electron microscope have a higher resolution than an optical microscope

A

Electron beam has a very short wavelength
Can distinguish between two objects only 0.1 nm apart

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43
Q

Why must a near vacuum be created within the chamber of an electron microscope

A

Electrons are absorbed and deflected by the molecules in the air

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44
Q

What are the 2 types of electron microscope

A

Transmission and scanning

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45
Q

How does a transmission electron microscope work?

A

Consists of an electron gun - produces beam of electrons - focused onto specimen by a condenser electromagnet
Beam passes through thin sections of specimen
Denser parts absorb more electrons and appear darker
Image is produced on a screen and can be photographed to give a photomicrograph

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46
Q

What are the limitations of both a scanning and transmission electron microscope ?

A

Resolution of 0.1 nm cannot always be achieved due difficulties in preparing specimen
High energy electron became stronger required - may destroy specimen
Complex staining process
No colour images
Specimen must be thin to allow electrons to penetrate - results in 2D images
Whole system must be in vacuum- living organisms can’t be observed
Images can contain artefacts

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47
Q

What is one difference in limitations between a scanning and transmission microscope

A

Specimen don’t have to be extremely thin in a scanning microscope as electrons don’t penetrate as beam of electrons are directed from above not below

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48
Q

What are the advantages of a scanning microscope

A

3D images can be produced

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49
Q

What are the disadvantages of a scanning microscope

A

Lower resolution
No view of internal structures

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50
Q

What two things do you use to measure specimens under a microscope?

A

Eye piece graticule & stage micrometer graticule

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51
Q

What is the equation for calculating length of internal organelles using scale bar

A

Image length of organelle
———————————— x actual length of scale bar
Image length of scale bar

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52
Q

What is cell fractionation

A

Process where cells are broken up and the different organelles are separated out

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53
Q

What is the order of pellets produced by the centrifuge in cell fractionation

A

Pellet 1: nucleus
Pellet 2: chloroplasts
Pellet 3: mitochondria
Pellet 4: Endoplasmic reticulum and lysosomes
Last pellet: ribosomes

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54
Q

Step by step of cell fractionation

A

Tissue we are extracting is placed into ice cold, isotonic and buffered solution
The cells are broken up by a homogeniser which releases the organelles - resulting fluid is the homogenate
Homogenate is then filtered to remove any complete cells or debris
Homogenate is then placed in test tube and spun in centrifuge.
It starts off being spun at low speeds to compress the heaviest organelles into a pellet at the bottom
The remaining fluid (supernatant) is then transferred to another test tube and spun in the centrifuge at a faster speed to compress the next heaviest organelles into a pellet at the bottom

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55
Q

What are the three stages of the cell cycle?

A

Interphase
Nuclear division (meiosis or mitosis)
Cytokinesis

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56
Q

What is the order of the phases in mitosis

A

Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

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57
Q

What is the importance of mitosis ?

A

Growth, Repair and Reproduction

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58
Q

Describe the interphase

A

Period before mitosis where the cell is not dividing and chromosomes are not visible.
The cellular activity that does take place, is…
DNA replication & the replication of organelles

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59
Q

Describe the structure of a chromosome after replication

A

2 chromatids held together by a centromere.
One short arm and one long arm

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60
Q

Describe the prophase

A

Chromosomes condense (shorten and thicken) to become visible
Nuclear envelope disintegrates and the nucleolus disappears.
Centrioles move to the poles and from them spindle fibres develop

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61
Q

What are spindle fibres collectively known as?

A

Spindle apparatus

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62
Q

Describe the metaphase

A

Spindle fibres form
Spindle fibres attaches the centromeres of chromosomes
Chromosomes line up at the equator by being pulled along the spindle apparatus

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63
Q

Describe the anaphase

A

Centromeres split
Chromatids are pulled by spindle fibres to opposite poles
Now refereed not as chromosomes
Energy for this process is provided by mitochondria that gather around spindle fibres

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64
Q

Describe the telophase

A

Nuclear envelope reforms around the chromosomes at the poles and the nucleolus reforms
Spindle fibres disintegrate
Chromosomes are no longer visible

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65
Q

Describe cytokinesis

A

The cytoplasm divides to form two cells with genetically identical nuclei (mitosis)

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66
Q

Describe the structure of a chromosome after replication

A

2 chromatids joined at a centromere.
Short arm and long arm

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67
Q

What is binary fission

A

Asexual reproduction of a single called organism such as bacteria
(Prokaryotes divide this way)

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68
Q

Describe the stages of binary fission

A

Circular dna replicates - both copies attach to cell membrane at opposite ends of the cell
Plasmids replicate
Cell membrane grows between dna and pinches inwards dividing the cytoplasm to form 2 daughter cells
New cell wall forms, dividing the original cell into 2 identical daughter cells, each with a single copy of circular DNA and a variable number of plasmid copies

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69
Q

What is cancer

A

A group of diseases caused by the growth disorder of cells

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70
Q

What are the 2 types of tumour? How does a tumour become cancerous?

A

Benign and Malignant
A tumour becomes cancerous if it changes from benign to malignant

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71
Q

How can the rate of mitosis be affected

A

The environment of the cell and growth factors

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72
Q

What causes uncontrolled mitosis

A

A mutation to one of the genes
Mutant cells formed are usually structurally and functionally different from normal cells. Most will die but any that survive are capable of dividing to form tumours

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73
Q

How can treatment of cancer affect cancerous cells?

A

Preventing dna from replicating
Inhibiting metaphase in mitosis by interfering with spindle formation

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74
Q

What are the effects of chemotherapy on normal cells

A

Normal cells that also divide rapidly can be vulnerable to same damage such as hair producing cells

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75
Q

How can you identify cancerous cells

A

Large variably shaped nuclei
Many dividing cells, disorganised arrangement
Variation in shape and size
Loss of normal features

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76
Q

How do you calculate mitotic index

A

(Number of cells it’s condensed chromosomes ÷ total number of cells) x 100

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77
Q

What can the mitotic index measure or help us predict

A

An elevated mitotic index indicates that more cells are dividing. This knowledge can be important in predicting survival and response to chemotherapy and cancer types

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78
Q

What’s the name of a membrane that’s around all types of cells

A

Plasma membranes

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79
Q

What does the cell-surface membrane do

A

-allows differnt conditions to be established inside and outside a cell
-controls movement of substances in and out of cell

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80
Q

Why are phospholipids an important structure to cell membranes

A

form a phospholipid bilayer
-hydrophilic heads on both layers are attractedwater
-hydrophobic tails are repelled by water
-allows lipid-soluble substances to enter and leave the cell
-prevent water soluble substances entering and leaving
-make membrane flexible and self-sealing

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81
Q

What forms do proteins come in in the cell membrane

A

Protein channels - form water filled tubes to allow water-soluble ions to diffuse across

Carrier proteins - bind to molecules or ions (eg: glucose and amino acids) and change shape to move these across the membrane

82
Q

The functions of the proteins in the cell membrane

A

-structural support
-act as channels (channel proteins) transporting water-soluble substances across it
-allow active transport across through carrier proteins
-from cell surface receptors for identifying cells
-help cells adhere together
-act as receptors (especially for hormones)

83
Q

Are cholesterol molecules in the cell membrane hydrophobic or hydrophilic?

A

Very hydrophobic

84
Q

Function of cholesterol molecules in the cell surface membrane

A

-reduce lateral movement of other molecules by pulling together fatty acid tails of phospholipids
-make membranes less fluid at high temperatures by adding strength
-prevents loss of water and dissolved ions by being very hydrophobic

85
Q

How are glycolipids made

A

Made up of carbohydrate covalently bonded with a lipid

86
Q

Function of glycolipids in the cell membrane

A

-act as cell recognition sites
-maintain stability of membrane
-help cells attach to each other for tissue formation

87
Q

How are glycoproteins formed

A

Carbohydrate chains attaching to extrinsic proteins on the outer surface of membrane

88
Q

Functions of glycoproteins in the cell membrane

A

-act as cell recognition sites
-help cells attach to one another to form tissue
-allows cells to recognise each other

89
Q

Permeability of cell surface membrane:
Why don’t most molecules freely diffuse across it?

A

-not lipid soluble so can’t pass through phospholipid belayer
-too large to pass through channel proteins
-have the same charge as channel proteins so are repelled
-polar so can’t pass through non-polar hydrophobic tails in bilayer

90
Q

What is a polar molecule

A

An electrically charged molecule

91
Q

What is the fluid mosiac model of the cell-surface membrane

A

They way molecules are combined and arranged into the structure of the cell membrane

92
Q

Why is the fluid mosaic model called it

A

Fluid - individual phospholipid molecules are moving relative to each other so gives membrane flexablilty to constantly change shape
Mosiac - proteins embedded in the phospholipid bilayer vary in shape size and pattern

93
Q

Is diffusion active or passive transport

A

Passive
Doesn’t require energy from external sources like ATP

94
Q

Why/how is simple diffusion a passive form of transport

A

-all particles are constantly in a random motion due to kinetic energy
-these particles are constantly bouncing off each other and off objects

So these particles move down a concentration gradient from area of high concentration to low

95
Q

Define diffusion

A

Net movement of particles from an area of high concentration to an area of low concentration until evenly distributed
Down a concentration gradient

96
Q

What types of molecules pass easily through cell membranes

A

Small non polar molecules like oxygen and co2

97
Q

Define facilitated diffusion

A

Movement of large or/and polar molecules across the cell membrane made easier (facilitated) by channel and carrier proteins
Passive process down a concentration gradient

98
Q

How does protein channels contribute to facilitated diffusion

A

Form water-filled hydrophilic channels.
Allow water-soluble ions to pass through membrane
They’re selective and only open to specific ions
The ion binds with protein causing it to change shape so it closes on side and opens on the other

99
Q

How does carrier protiens contribute to facilitated diffusion

A

Specific molecules (like glucose) bind to the carrier protein causing protein to change shape so that the molecule is released into the membrane.
No external energy (like ATP) is needed as the molecule moves from a area of high concentration to an area of low concentration by using kinetic energy from the molecules

100
Q

Define osmosis

A

The net movement of water molecules from an area of high water potential (dilute solution) to an area of low water potential (concentrated solution) down a concentration gradient (passive transport).
Through a selectively permeable membrane

101
Q

What Greek letter represents water potential and how’s water potential measured

A

letter ψ (psi)
Measured in units of pressure usually kiloPascals (kPa)

102
Q

Define water potential

A

The pressure created by water molecules.
Under standard conditions of temperature and pressure (25°c and 100kPa)

103
Q

What’s the water potential of pure water

A

0 kPa

104
Q

(In osmosis) Will the addition of a solute to pure water lower or higher it’s water potential

A

Lower

The more solute that’s added (the more concentrated the solution) the lower (more negative) it’s water potential

105
Q

(In osmosis) what must the water potential of a solution (solute+water) be?

A

Less than zero / a negative value

106
Q

How does the value of water potential change in osmosis

A

Water will move from an area of higher (less negative) water potential to one of lower (more negative) water potential

Eg:
From -20kPa to -30kPa

107
Q

In osmosis what motion are the solute and water molecules

A

Random motion due to their kinetic energy

108
Q

What type of molecules does the partially permeable membrane allow to cross and not cross

A

Allows water molecules to cross
But not solute molecules
From a higher water potential to the lower water potential

109
Q

What happens if red blood cells are put in pure water

A

It will absorb water by osmosis as it has a lower water potential
Until cell surface membrane bursts and releasing its contents (haemolysis)

110
Q

In osmosis:
If water potential of external solution is higher (less negative) than the cell solution what happens

A

Net movement of water enters the cell
Cell swell and bursts/lysis (only bursts if it’s animal cell because they don’t have cell walls)

If it’s a red blood cell then cell is hypotonic by cytolysis
If plant cell then cell becomes turgid

111
Q

In osmosis
If water potential of external solution is equal than the cell solution what happens

A

Net movement of water neither enters or leaves the cell as it’s in equilibrium
State of cell doesn’t change

If red blood cell then cell is isotonic
If plant cell then incipient plasmolysis occurs

112
Q

In osmosis:
If water potential of external solution is lower (more negative) than the cell solution what happens

A

Net movement of water leaves the cell
Cell shrinks / shrivels / plasmolysed

If red blood cell then cell is hypertonic by plasmolysis and cell is darker as haemoglobin is more concentrated
If plant cell then cell is just plasmolysed

113
Q

Define active transport

A

Movement of molecules or ions into or out of a cell from a pj area of lower concentration to an area of higher concentration using ATP and carrier proteins going against the concentration

114
Q

What is ATP used for in active transport

A

-directly move molecules
-co-transport

115
Q

How does passive and active transport differ

A

Active:
-needs metabolic energy from ATP
-it’s against the concentration gradient
-uses carrier protein molecules which act as ‘pumps’
-very selective

116
Q

Describe the process of direct active transport of a single molecule or ion

A

-carrier proteins span the plasma membrane and bind to molecule/ion
-molecule/ion binds to receptor sites on the carrier protein
-on the inside of cell, ATP binds to protein, causing it to split into ADP and a phosphate molecule
-causing protein to change shape and opens to the opposite side of membrane
-molecule/ions released to other side of membrane
- the phosphate molecules released from protein causing it to revert to its original shape
-phosphate molecule and ADP resyntheisise into ATP during respiration

117
Q

Describe the sodium-potassium pump

A

Sodium ions are actively removed from cell/organelle
While potassium ions are actively taken in
Simultaneously

118
Q

What does cotransport use to move substances into and out of cells and which cells specifically

A

Uses ions
Particularly in epithelial cells of the ileum

119
Q

Describe the process of co-transport in the ileum

A

-sodium and potassium ions are pumped out of epithelial cells by active transport into the blood by the sodium-potassium pump through specific carrier proteins
-leaving a lower concentration in the cell
-these ions move in from the lumen by facilitated diffusion which brings in glucose and amino acids into the cell
-these then diffuse from a high concentration in cell to low concentration in blood

120
Q

What are the 2 ways rate of movement across membranes is increases in co-transport

A

-epithelial cells in the ileum have microvilli which has a large surface area for insertion of carrier proteins for diffusion, facilitated diffusion and active transport
-increase number of protein channels and carrier proteins in any given area of membrane

121
Q

Describe how exocytosis and endocytosis moves molecules through cell membranes

A

Transports large molecules
These particles are enclosed in vesicles made from cell membrane and transported into cell in endocytosis
In exocytosis, vesicles containing large particles are fused with cell membrane and released from cell

122
Q

Rate of gas exchange by diffusion becomes more rapid as…

A
  • surface area increases
    -diffusion distance decreases
    -diffusion gradient becomes steeper
    -temperature increases
123
Q

Define an infection

A

An interaction between the pathogen and the body’s various defence mechanisms resulting in individuals death or recovery from disease

124
Q

How do you recognise your own cells

A

By lymphocytes distinguishing between self cells and non-self cells (foreign cells)

125
Q

Difference between bacteria and viruses

A

Bacteria:
Prokaryotic cells - circular strand of DNA
Doesn’t need a host to survive
Bigger
Have: membrane, wall, cytoplasm and membrane bound organelles

Viruses:
Consists of just nucleic acid enclosed in a protein coat
genetic material in form of DNA or RNA
Require a host cell to survive
Smaller
Have no membrane bound organelles

126
Q

3 Physical barriers to infection

A

Skin - consists of keratin
Stomach acid - HCl which kills bacteria
Guy and skin flora - natural bacterial flora competes with pathogens for food and space

127
Q

Examples of Nonspecific responses of the body to infection

A

-inflammation
-lysozymes action
-interferon
-phagocytosis

128
Q

What is done to minimise the effect of tissue rejection

A

Donor tissues for transplant are matched as closely as possible to the recipient (best matches come from relative that are genetically close)
Immunosuppressant drugs are often administered to reduce the keel of the immune response that still occurs

129
Q

What are 2 examples of the non-specific immune response

A

Physical barriers
Phagocytosis

130
Q

What are 2 examples of the specific immune response

A

Cell mediated response (involving t-lymphocytes)
Humoural response (involving b-lymphocytes)

131
Q

What are the two types of white blood cell

A

Phagocytes and lymphocytes

132
Q

When does phagocytosis occur and why?

A

If a pathogen tries to infect the body, the body’s first line of defence is the physical and chemical barriers - should this fail, the next line of defence is phagocytosis

133
Q

Give the step by step process of phagocytosis

A
  1. Chemical products of pathogens or dead, damaged and abnormal cells act as attractants causing phagocytes to move towards the pathogen.
  2. The receptors on the cell surface membrane of the phagocyte recognise and attach to chemicals on the surface of the pathogen
  3. They engulf the pathogen to form a vesicle, known as a phagosome
  4. Lysosomes move towards vesicles and fuse with it
  5. Lysozymes break down the pathogen by hydrolysis
  6. The soluble products from the breakdown are absorbed into the cytoplasm of the phagocyte
134
Q

Define immunity

A

The ability of organisms to resist infection by protecting against pathogens or their toxins that invade their bodies. Involves recognising foreign material (antigens)

135
Q

Define agglutination

A

The clumping together of cells or particles caused by antibodies which assists phagocytosis

136
Q

Define antibody

A

A protein specific to an antigen, produced by plasma cells

137
Q

Define antigen

A

Foreign/non-self proteins on the surface of cells that stimulate an immune response.

138
Q

Define pathogen

A

Microorganism that causes communicable diseases eg: bacteria, viruses, fungi, protists/protocista

139
Q

Describe viral structure

A
  • acellular - non living
    -smaller than bacteria
    -contains nucleic acids such as DNA or RNA as genetic material, enclosed within a protein called the capsid
    -can only multiply inside living host cells
    -some like HIV has a lipid envelope. If not present the capsid has attachment proteins which are essential in allowing the virus to identify and attach to a host cell.
140
Q

What are the two types of lymphocyte

A

B lymphocytes
T lymphocytes

141
Q

Where do b lymphocytes mature

A

Bone marrow

142
Q

Where do t lymphocytes mature

A

In the thymus gland

143
Q

How can t-lymphocytes distinguish invader cells from normal cells

A

Antigens displayed on cell surface membranes

144
Q

What are cells that display foreign antigens called ?

A

Antigen-presenting cells

145
Q

What are the stages in the response of a t-lymphocyte to infection by a pathogen
(cell mediated immunity)

A
  1. Pathogens invade body cells or are taken in by phagocytes
  2. Phagocyte places antigens from the pathogen on its cell-surface membrane
  3. Receptors on a specific helper T cell fit exactly onto these antigens
  4. This attachment activates the T cell to divide rapidly by mitosis and form clones
  5. Cloned t -cells destroy the pathogen
146
Q

What are the 4 ways the cloned t - cells can destroy pathogens ?

A

Develop into memory cells
Stimulate phagocytes to engulf pathogens by phagocytosis
Stimulate b-cells to divide and secrete antibodies
Activate cytoxic T cells

147
Q

How do cytoxic T cells kill infected cells?

A

Produce a protein called PEFORIN that makes holes in the cell surface membrane
Allows cell membrane to become freely permeable to all substances and as a result the cell dies

148
Q

Why is humoral immunity called humoral immunity ?

A

Because it involves antibodies that are soluble in blood and tissue fluid of the body

149
Q

Describe the function of plasma cells

A

Secrete antibodies into blood plasma that lead to the destruction of the antigen
Survive for only a few days
Can secrete around 2000 antibodies each second

150
Q

What aspect of the immune response are plasma cells responsible for

A

Immediate defence - PRIMARY immune response

151
Q

What aspect of the immune response are memory cells responsible for

A

SECONDARY immune response

152
Q

What do memory cells do

A

Live considerably longer than plasma cells - long term immunity
When they encounter the SAME antigen at a later date they divide rapidly and develop into plasma cells and more memory cells
The plasma cells produce antibodies to destroy the pathogen

153
Q

Give the step by step process that explains the role of B lymphocytes
(humoral immunity)

A
  1. The surface antigens of an invading pathogen are taken up by a b-cell by endocytosis
  2. The B cell processes and presents the antigens
  3. Activated helper T cells attach to processed B cells, thereby activating it
  4. B cell divides by mitosis to give clones of plasma cells
  5. The cloned plasma cells produce and secrete the specific antibody
  6. The antibody attaches to the antigens on the pathogen and destroys it
154
Q

Describe the binding sites of an antibody

A

Each antibody has 2 identical binding sites complimentary to a specific antigen.
The variable region

155
Q

What is the variety of antibodies down to

A

The binding site consists of a sequence of amino acids that form a specific 3D shape that binds directly to a specific antigen

156
Q

Describe the structure of an antibody

A

Made up of 4 polypeptide chains
- chains of one pair are long and called heavy chains
-chains of the other pair are shorter and called light chains
Each antibody has a specific binding site (known as the variable region)
The rest of the antibody is known as the constant region

157
Q

How can the antibody lead to the destruction of the pathogen in a bacterial cell

A

-Cause agglutination of the bacterial cells making it easier for phagocytes to locate them
-Serve as markers that stimulate phagocytes to engulf bacterial cells to which they are attached

158
Q

What is a monoclonal antibody

A

Clones of one specific antibody produced by B cells

159
Q

How are monoclonal antibodies useful in medical diagnosis

A

Example -prostate cancer in men
Men with prostate cancer produce more of a protein called PSA leading to unusually high levels of it in the blood
By using a monoclonal antibody which interacts with this antigen, it is possible to obtain a measure of the level of PSA in the blood.
(Although not enough to diagnose the disease itself it gives early warning)

160
Q

Give the step by step process of how monoclonal antibodies are formed

A
  1. A mouse is exposed to the non-self material against which an antibody is required
  2. The B cells in the mouse produce a mixture of antibodies which are extracted from its spleen
  3. To enable the B cells to divide outside the body they are mixed with cancer cells
  4. Detergent is added to the mixture to break down the cell surface membranes of both types of cell and enable them to fuse - HYBRIDOMA
  5. The hybridoma cells are separated under a microscope and each single cell is cultured to form a clone
  6. Each clone is tested to see whether it produces the required antibody
  7. Any clone that does, is grown on a large scale and the antibodies are extracted from the growth medium
161
Q

How are monoclonal antibodies used in direct monoclonal antibody therapy

A

Targets medication to specific cells
- attach a therapeutic drug to an antibody
-monoclonal antibodies can be produced that are specific to antigens on cancer cells
-antibodies are given to patient and they attach themselves to receptors on cancer cells
-they block chemical signals that stimulate uncontrolled growth

162
Q

What are the advantages of antibodies

A

Highly specific & non toxic so have fewer side effects

163
Q

How are monoclonal antibodies used in indirect monoclonal antibody therapy & what are the benefits

A

Radioactive / cytotoxic drug is attached to monoclonal antibody which attaches to cancer cells and kills them
- can be used in smaller doses as targeted to specific sites
- cheaper and reduces side effects

164
Q

How do pregnancy tests work?

A

3 components : reaction site , test site & control site
Relies on presence of hormone hcG produced by the placenta & found in urine

165
Q

Why is the presence of a fixed antibody at the control site of the test strip important ?

A

Prevents false negative results
If no antigen antibody complex is formed then the free antibody & dye substrate will continue to travel up the stick not binding to any hcG protein.
The fixed antibody at the control site traps the free antibody & dye substrate and produces a coloured line

166
Q

Describe how a positive pregnancy test is acquired

A

The hcG antigens bind with the antibodies, the hcG antibody colour complex moves along the strip until it’s trapped by a different type of antibody which produces a coloured line

167
Q

3 uses of monoclonal antibodies that raise ethical issues

A

-production of it involves use of mice - involves injecting tumour cells into mice, inducing cancer. Questions whether animals should be used this way
- there’s been deaths associated with their use use in treatment of multiple sclerosis. Important that patients know risks and benefits of the drugs and there’s informed consent
-testing for safety of new drugs present certain dangers. Issues about the conduct of drug trials involving them.

168
Q

What are the 2 types of immunity

A

Passive
Active

169
Q

What are the 2 types of active immunity

A

Natural active immunity:
Individual becomes infected with disease under normal circumstances. Body produces own antibodies and continues to do so for many years

Artificial active immunity:
Forms basis of vaccination (immunisation).
Involves inducing an immune response in an individual, without them suffering the symptoms of disease

170
Q

Define vaccination

A

Introduction of dead or inactive pathogens with its antigens (or mRNA) to stimulate an immune response and provide long term immunity by stimulating production of memory cells

171
Q

Stages of vaccination

A

-vaccine contains the specific antigen
-antigen is displayed on surface of an antigen presenting cell (eg: phagocytes)
-specific T-helper cells with complementary receptor binds to the antigen
-this activates B-cells with complementary antibody
-B-cells form many clones through dividing by mitosis
-differentiate to form plasma cells which produce antibodies
-some T-cells and B-cells develop into memory cells for a secondary immune response

172
Q

Features of a successful vaccination programme

A
  • economically available in sufficient quantities to immunise most of the vulnerable population
    -few side effects
    -means of producing, storing and transporting the vaccine
    -means of administering the vaccine properly at the appropriate time
    -ability to vaccinate the vast majority of vulnerable population to produce herd immunity
173
Q

Describe the primary immune response in vaccinations

A
  • first immune response to a pathogen/antigen
    -longer lag time (slower) - no memory cells present
    -phagocytosis, T-cells and B-cells involved - clonal selection
    -pathogens multiply and damage host cells - feel symptoms
  • T-cells and B-cells become memory cells
174
Q

Describe secondary immune response in vaccinations

A

-secondary infection by the same pathogen/antigen
-shorted lag time (faster)
-more antibodies produced
-rate of antibody production is faster
-memory T-cells and B-cells become Killer T-cells and plasma cells by clonal expansion
-don’t feel symptoms

175
Q

Reasons for vaccination failure

A

-fails to induce immunity in certain individuals eg: people with defective immune systems
-may develop disease immediately after vaccination, before immunity levels are sufficient enough. Have the potential to then infect others
- pathogen may mutate frequently - antigens change suddenly - vaccines ineffective (antigenic variability)
-many varieties of a particular pathogen = impossible to develop a vaccine effective against them all.

176
Q

Define herd immunity

A

Arises when a sufficiently large amount of population has been vaccinated to make it difficult for a pathogen to spread within that population (as pathogens are passed from individual to individual when in close contact.)

It’s highly improbable that a susceptible individual will meet an infected individual = those that are immune are also protected

177
Q

Define clonial expansion

A

The production of many genetically identical daughter cells through cell division of the activated B or T lymphocyte after clonial selection

178
Q

Define clonal selection:

A

Process of matching the antigens on an antigen presenting cells with the antigen receptors on B or T lymphocytes

179
Q

What’s the MMR vaccine?

A

A combined vaccine for measles, mumps and rubella.
Replaces 3 separate vaccines

180
Q

How is passive immunity produced ?

A

produced by the introduction of antibodies into an individual from outside source = no direct contact with pathogen or antigen is necessary to induce immunity. (acquired immediately)

181
Q

Why is passive immunity not long lasting ?

A

Antibodies aren’t being produced by the individual themselves.
Antibodies aren’t replaced when they’re broken down
no memory cells are formed
= no lasting immunity.

182
Q

Describe the structure of the HIV virus

A

Outside- lipid envelope which has attachment proteins embedded
Inside the envelope- capsid that encloses the 2 single strands of RNA & some enzymes
One of these enzymes - reverse transcriptase (means the virus is part of a group called retroviruses)

183
Q

What is reverse transcriptase

A

Catalyses the production of DNA from RNA

184
Q

Give the steps in the replication of the HIV virus

A
  • HIV enters the bloodstream & circulates
  • HIV readily binds to protein called CD4 (on tH cells)
  • the protein capsid fuses with the cell surface membrane (rna &enzymes of HIV enter the tH cell)
  • reverse transcriptase coverts the HIV viruses RNA into DNA
  • New DNA is moved to tH cell’s nucleus where it’s inserted into the cell’s dna
  • the HIV DNA creates mRNA which contains instructions for making new viral proteins
  • mRNA passes out of the nucleus through pores and uses the cell’s protein synthesis mechanisms to make HIV particles
  • HIV particules break away from tH cell with a piece of its cell surface membrane which forms the lipid envelope
185
Q

How does HIV cause the onset of AIDS

A

HIV specifically attacks tH cells & interferes with their normal functioning leading to the onset of AIDS
An uninfected person normally has 800-1200 tH cells per mm^3 of blood wheras in a person suffering from AIDS this number can be as low as 200

186
Q

In AIDS, what is the negative effect of having a low number of tH cells and how is it caused ?

A

tH cells are important in cell mediated immunity
Without a sufficient number of tH cells the immune system cannot stimulate B cells to produce antibodies or tC cells that can kill cells infected by a pathogen
Memory cells may also become infected and destroyed
As a result the body is unable to produce an adequate immune response & as a result becomes more susceptible to other infections & cancers

187
Q

What is the ELISA test

A

Uses antibodies to not only detect the presence of a protein in a sample but also its quantity.
Extremely sensitive & can detect very small amounts of a molecule

188
Q

Give the step by step process of how the ELISA test works (eg. We are looking for a protein and in this case an antigen)

A
  • Apply the sample to a surface (slide), to which all the antigens in the sample will attach
  • Wash the surface multiple times to remove unattached antigens
  • Add the antibody that is specific to the antigen we are trying to detect & leave to bind together
  • Wash the surface to remove excess antibody
  • Add 2nd antibody that binds with the 1st antibody (The 2nd will have an enzyme attached)
  • Add the colourless substrate of the enzyme - the enzyme will act on this to change it into a coloured product
  • The amount of antigen that’s present is relative to the intensity of the colour that develops
189
Q

How do antibiotics work (bacterial cell walls specifically)

A

Antibiotics can prevent bacteria from making normal cell walls
In bacteria cells (like plants) water enters constantly by osmosis
The cell doesn’t burst due to the murein cell wall (inelastic)
Antibiotics such as penicillin inhibit certain enzymes required for synthesis & assembly of peptide cross-linkages in bacterial cell walls
This weakens the walls making them unable to withstand pressure - cell burst & bacterium dies

190
Q

Why are antibiotics ineffective against viral diseases like AIDS ?

A

Viruses rely on a host cell to carry out their metabolic activities & therefore lack their own metabolic pathways and structures= there are no metabolic mechanisms / structures for antibiotics to disrupt
Viruses also have a protein coat instead of a murein cell wall & do not have sites where the antibiotics can work.
In any case, when viruses are within an organisms own cells, antibiotics cannot reach them

191
Q

How is active immunity produced?

A

Produced by production of antibodies by individuals own immune system. Direct contact with pathogen or antigen needed. Immunity takes time to develop
Generally long lasting.

192
Q

Why is it best to vaccinate a population at one specific time to increase herd immunity ?

A

As it interrupts the spread of the pathogen

193
Q

Why is herd immunity important

A

Important as not everyone can be vaccinated eg: young children and people with allergies to the vaccination

194
Q

What was the controversy associated with the MMR vaccine & what did it result in?

A

a study suggested there was a higher incidence of autism among children who had recieved the MMR vaccine than those who recieved the 3 separate vaccines

Lots of parents opted for their child to have no vaccine (leaving their child unprotected) or the 3
separate vaccines

Many scientists suggest it was just a correlation between 2 factors

195
Q

How can AIDS lead to death

A

The body can’t produce an adequate immune response so is susceptible to infections and cancers
Pathogens with therefore reproduce, damage cells and release toxins

196
Q

Why does the fact that HIV rapidly enters host cells mean a vaccine is harder to develop and be effective ?

A

HIV enters the cells before antibodies can bind to it and are therefore not able to reach the HIV and destroy it

197
Q

Compare scanning electron microscope and transmittion electron microscope

A

TEM:
Higher resolution
Produces image of internal structures only
Produces 2D image
Selections must be thin - one cell thick

SEM:
Lower resolution
Produces image of external structures only
Produces 3D image
Sections must be thicker than TEM

198
Q

Compare optical and electron microscope

A

Electron:
Uses a beam of electrons
Much greater resolution
Focused using magnets
Smaller structures are visible
Specimen must be dead
Image not in colour

Optical:
Uses a beam of light
Relatively low resolution
Focused using glass lenses
Smaller structures are not visible
Specimens can be living
Image in colour

199
Q

What’s a macrophage cell

A

Type of white blood cell which is a phagocyte which presents antigens on its surface to present them to B or T cells

200
Q

Describe limiting water loss in insects

A

In Terrestrial insects, water easily evaporated from their body surface so they can become dehydrated.

201
Q

What are the properties of molecules that can diffuse through the phospholipid bilayer quickly without transport proteins

A

Lipid soluble
Small
Non-polar (not charged)

A Level Biology AQA (5 decks)

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