Cells Flashcards
(168 cards)
1
Q
Cell membrane
A
Structure- consists of a phospholipid bilayer where channel proteins and carrier proteins are found
Function- physical barriers which allows some molecules to pass through
2
Q
Nucleus
A
Structure- double membrane called a nuclear envelope which has nuclear pores. Contains chromatin which consists of DNA and a nucleolus which is the site of ribosome production
Function- controls the functions of the cell e.g protein synthesis
3
Q
Mitochondria
A
Structure- oval shaped with outer membrane and inner membrane which is highly folded to form cristae with matrix on the inside contains enzymes for respiration
Function- site of aerobic respiration and produces ATP
4
Q
Chloroplast
A
Structure- have a double membrane that surrounds a gel like stroma. Within the stroma there are thylakoids which contain photosynthetic membranes
Function- photosynthesis takes place within thylakoid membranes
5
Q
Golgi apparatus
A
Structure- fluid filled flattened are curved sacs with vesicles surrounding the edges
Function- responsible for processing and packaging lipids and proteins. Also produces lysosomes
6
Q
Lysosomes
A
Structure- type of Golgi vesicle with no obvious internal structure surrounded by a membrane and contains digestive enzymes called lysozymes
Function- responsible for digesting invading cells, old unwanted parts of cells. Releases hydrolytic enzymes
7
Q
Ribosomes
A
Structure- composed of two sub units consists of ribosomal proteins and rRNA
Function- responsible for for synthesising proteins and site of protein production
8
Q
Rough endoplasmic reticulum
A
Structure- series of flattened sacs enclosed by a membrane. RER has ribosomes attached along the outer surface. Has a large surface area to increase rate of protein synthesis
Function- process and produces proteins
9
Q
Smooth endoplasmic reticulum
A
Structure- no ribosomes along the outer surface, system of membrane sacs
Function- responsible for processing and packaging lipids
10
Q
Cell wall
A
Structure- rigid structures surrounding the cell membrane and is composed of cellulose
Function- maintain cell shape by providing structural support
11
Q
Cell vacuole
A
Structure- permanent pockets of cell sap
Function- maintains osmotic pressure inside the cell to ensure plant cells remain turgid
12
Q
How are prokaryotes different to eukaryotes
A
Prokaryotes are much smaller, they lack a nucleus and other membrane bound organelles, smaller ribosomes, cell wall that contains murein, a glycoprotein
13
Q
Capsule
A
Protects cell from viruses and helps to retain moisture
14
Q
Ribosomes
A
Smaller than eukaryotic ones
Site of protein synthesis
15
Q
DNA
A
In single circular loop
16
Q
Plasmids
A
Small circular pieces of DNA
17
Q
Cell wall (prokaryotic)
A
Rigid outer covering made of murein
18
Q
Flagellum
A
A tail like structure which rotates to move the cell
19
Q
Mesosomes
A
Infoldings of the inner membrane which contain enzymes required for respiration
20
Q
Pilli
A
Hair like proteins which help attachment to other cells
21
Q
Are viruses living or not
A
They are acellular and non living
22
Q
Structure of viruses
A
Consist of nucleic acid (DNA or RNA) enclosed in a protective protein coat called the capsid and sometimes covered in a lipid layer called the envelope
There are also attachment proteins
23
Q
Viral replication
A
- viruses attaches its attachment proteins to host cells membrane surface receptor
- genetic material (DNA or RNA) is released into host cell
- viral proteins and genetic material is replicated by host cells enzymes
- new virus particles assemble
- viruses are released from the host cell, usually destroying and bursting the cell in the process
24
Q
Binary fission
A
- circular DNA and plasmids replicate
- cell membrane grows dividing the cytoplasm and a new cell wall also forms
- two daughter cells produced each contains one circular DNA copy and many plasmids
25
What cell undergo binary fission
Prokaryotic cells
26
Why can viruses not undergo cell division
They are non living
27
What is Magnification
The size of the object
28
What is Resolution
The level of detail (clear)
The ability to distinguish between 2 separate objects
29
Light (optical) microscopes
Max magnification of x1500 and resolution of 200nm
Specimens are illuminated with light
Stain cells to make visible
Wavelength between photons of light is longer
30
Two types of electron microscope
SEMs scanning electron microscope
TEMs transmission electron microscope
31
Electron microscopes
Higher magnification and resolution
Used to view smaller objects in greater detail
32
SEMs
3D image
An electron beam is scanned across the specimen and this displaces electrons from the specimens surface and then the electrons are collected to form an image
Can be used on thick specimens
33
TEMs
2D
A beam of electrons is transmitted through a thin section of a specimen.denser parts of specimen absorb more so appears darker
34
Limitation of electron microscopes
- whole system must be in a vacuum so living specimens cannot be viewed
- complex staining process is required which many introduce artefacts into the image
-specimens have to thin especially for TEM
- SEM has a lower resolving power than TEM but both greater than the optical microscope
35
What is cell fractionation
The process in which different parts of the cell are separated so organelles can be studied in detail
36
Two types of cell fractionation
Differential centrifugation
Density gradient centrifugation
37
Why are cell prepared in a cold isotonic buffered solution
Cold- reduce enzyme activity
Isotonic- prevent organelles from shrinking and bursting
Buffered- maintain constant pH to prevent enzymes denaturing
38
What are the two step processes in cell fractionation and what happens in each
Homogenisation- cell is broken using a blender and solution is filtered
Ultracentrifugation- solution is spun at a high speed
39
What does the centrifugal forces cause to happen
Causes pellets of the most dense to form at the bottom then solution is spun at a high speed with increases each time
40
What is the order of centrifugation
Nuclei
Mitochondria
Lysosomes
ER
Ribosomes
41
What is the role of mitosis and the cell cycle
Produce identical daughter cells
42
Stages of cell cycle
Interphase- cell grows organelles duplicate DNA replicates
Mitosis- cell division
Cytokinesis- cell cytoplasm divides to from two identical daughter cells
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Why is mitosis important
Growth
Repair
Reproduction in some single celled organisms
44
What is a chromatid
One arm of a newly copied chromosome
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What is a centromere
Joins chromatids together
46
What occurs during Prophase
Chromosomes become smaller and condense
Spindle fibres from each centriole
Nuclear envelope disintegrates and nucleolus disappears
47
What occurs during Metaphase
Chromosomes arrange themselves at equator of the cell
They attach to spindle fibres
48
What occurs during Anaphase
Rapid stage
Centromere divides and spindle fibres contract which pulls chromatids to opposite poles
49
What occurs during Telophase
Chromosomes uncoil and become chromatin
Nucleoli reappears and nuclear membrane reforms
Spindle fibres disappear
50
What is cancer
Uncontrolled mass or growth of cells
51
What causes cancer
Mutations to genes
52
What is a benign tumour
Non cancerous
Contained within a membrane
53
What is a malignant tumour
Cancerous
54
What is apoptosis
Programmed cell death
55
What is metastasis
Moves through the blood
56
What does a cell membrane control
They are partially permeable so control which substances can enter and leave a cell
57
What does a cell membrane act as
A barrier
58
What organelles have a double membrane
Mitochondria and nucleus
59
Why are cell membranes described as the fluid mosaic model
Fluid- phospholipids are constantly moving
Mosaic- proteins are scattered
60
What are the components of a cell membrane
Phospholipid bilayer
Membrane proteins
Glycoproteins
Glycoproteins
Cholesterol
61
What is a phospholipid bilayer
Forms a barrier but centre is hydrophobic but allows small, no polar molecules like carbon dioxide to diffuse through
62
What are intrinsic proteins and examples
Spam from one side of the phospholipid bilayer to the other
Carrier and channel proteins
63
What are extrinsic proteins and examples
Occurs in surface of the lipid bilayer
E.g receptors
64
What are glycoproteins
Proteins with a carbohydrate attached
65
What are glycolipids
Lipid with a carbohydrate attached
66
What are the role of glycoproteins and glycolipids
Act as antigens
Act as recognition sites
Help cells attach to one another to form tissues
67
What is cholesterol
Type of lipid between the phospholipids which restricts the movements of other molecules
Very hydrophobic acts as a barrier
68
How does cholesterol give the cell membrane stability
By binding to tails of phospholipids which causes them to pack together so reduces movement
69
How can permeability be determined
Amount of movement and gaps
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What affects permeability
Temperature
Solvents
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How does a temperature below 0 affect permeability
Phospholipids pack closely together, channel and carrier proteins denature which increases permeability and ice crystals form which pierces membrane
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How does a temperature between 0 and 45 degrees affect permeability
Phospholipids move around freely
As temp increases so does kinetic energy so permeability increases
73
How does temperature above 45 degrees affect permeability
Phospholipids start to melt so membrane becomes more permeable
Water inside cell expands putting pressure on the membrane
Channel and carrier proteins denture which increases permeability
74
How do solvents affect the permeability of membranes
They can insert themselves into the bilayer and from hydrogen bonds with a phospholipid molecule near the ester bond
This pushes phospholipids out of their orderly placements and increases their movement, this disrupts the membranes structure so increasing its permeability
Solvents also denature proteins by disrupting bonds
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What is simple diffusion
Movement of particles from an area of high concentration to an area of low concentration until equilibrium is reached
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Is simple diffusion active or passive process
Passive process
Down the concentration gradient
77
Example of simple diffusion
Oxygen and carbon dioxide in alveoli
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What are the 4 factors affecting the rate of simple diffusion
Concentration gradient- greater concentration gradient faster diffusion
Membrane thickness- thinner membrane faster diffusion
Surface area- larger surface area faster diffusion
Temperature- higher temp faster diffusion
79
What is facilitated diffusion
Diffusion that occurs through specific intrinsic proteins in the cell membrane called carrier proteins and channel proteins
80
Why do large polar molecules require to diffuse through specialised carrier or channel proteins
They move very slowly without
81
What is the role of carrier proteins
Move large molecules across the membrane
82
How do carrier proteins work
Large molecules attach then the protein changes shape releasing the molecule on the other side of the membrane
83
What is the role of channel proteins
Form pores for charged particles to diffuse through
84
How do protein channels work
No changing shape, simple tunnel which allows charged particles to cross the membrane
85
What are the 2 factors that affect the rate of facilitated diffusion
Concentration gradient- greatest concentration gradient after facilitated diffusion
Number of channel or carrier proteins- greater number faster facilitated diffusion, but only until a certain point once all proteins are in use facilitated diffusion cannot happen any faster
86
What is osmosis
Movement of water molecules from a region of high water potential to an area of low water potential through a partially permeable membrane
87
What is water potential
The likelihood of water molecules to diffuse out of or into a solution
88
What is the water potential of pure water
Zero
89
What does adding solutes do to the water potential
Decreases it to below zero
More negative
90
What is an isotonic solution
Same concentration of solutes and solvents
91
What is a hypertonic solution
More solutes less solvents
92
What is a hypotonic solution
Fewer solutes, more solvents
93
Where will water always move to
Where there are more dissolved solutes
94
What happens to an animal cell in a hypotonic solution with a higher water potential
Water enters the cell and it swells and bursts
95
What happens to an animal cell in an isotonic solution
Water neither enters or leaves cell
No change to state of cell
96
What happens to an animal cell in a hypertonic solution with a lower water potential
Water leaves the cell and it shrinks and shrivels
97
What happens to a plant cell in a hypotonic solution with a higher water potential
Water enters the cell causing it to swell but it doesn’t burst as the cell wall protects ad cell become turgid
98
What happens to a plant cell in a isotonic solution
Water neither enters or leaves cell
99
What happens to a plant cell in a hypertonic solution with a lower water potential
Water leaves the cell but plant cells are protected from shrinking but vacuole shrinks then cell membranes pull away from cell wall (plasmolysis)
100
What are the 3 factors that affect the rate of osmosis
Water potential gradient- higher water potential gradient faster osmosis
Membrane thickness- thinner membrane faster osmosis
Surface area- larger surface area faster osmosis as more molecules can move across in the same amount of time
101
What is active transport
Movement of particles from an area of low concentration to an area of high concentration against the concentration gradient using ATP and carrier proteins
102
What is ATP hydrolysed into
ADP and Phosphate molecule
103
What are the 3 factors that affect the rate of active transport
Speed of carrier proteins- faster movement faster active transport
Number of carrier proteins- more proteins means more active transport
Rate of respiration- greater rate means more ATP produced so more active transport
104
What is co trasnport
Active transport that uses a type of carrier proteins called co transporters which bind two molecules at a time
One moves down its concentration gradient and this is used to move the other molecule across the membrane against its concentration gradient
105
What is an example of co transporters
Glucose form small intestine to blood
106
What is the process of co transport of glucose
Na ions are actively transported into the blood by a sodium potassium pump. This creates a concentration gradient as there is more sodium in the ileum than the epithelial cell
The concentration gradient causes Na ions to diffuse from the ileum into the epithelial cell down their concentration gradient through the sodium glucose co transporter protein . Glucose enters the cell with sodium
There is a higher concentration of glucose in the epithelia cell than the blood so glucose diffuses down its concentration gradient through a channel protein via facilitated diffusion
107
What is an antigen
A molecule on the surface membrane that triggers an immune response
108
What do antigens enable the immune system to identify
Pathogens
Abnormal body cells e.g cancer cells
Toxins
Cells from other organisms of the same species
109
What are the types of white blood cells
Phagocytes and lymphocytes
110
What are phagocytes
A white blood cell that digests and breaks down pathogens by phagocytosis
111
What are the two types of phagocytes
Neutrophils and Macrophages
112
What do macrophages do
At end of phagocytosis they present the pathogens antigens on its surface membrane (APC) to recruit lymphocytes to attack pathogen
113
What are the two types of lymphocytes
T-lymphocytes and B-lymphocytes
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What is phagocytosis
Cellular process of engulfing particles using the cell membrane- Carried out by phagocytes
115
What is the process of phagocytosis
Pathogen receptor proteins attach to the phagocytes surface receptor proteins
Pathogen is engulfed by phagocyte to form a phagosome
Lysosomes fuse to phagosome to form a phagolysosome and release H2O2, HCl and digestive enzymes
Harmless products are removed
Phagocyte then presents the pathogens antigens on its surface membrane making it can antigen presenting cell
116
What is the phagocyte called when it presents the pathogens antigens on its cell surface membrane
Antigen presenting cell (APC)
117
What does the cell mediated response involve
T-lymphocytes
118
How to T- cells respond to the APC
T-helper cells have receptors that allows them to fit exactly to the presented antigens
119
What do T-helper cells do
Stimulate phagocytes for further phagocytosis
Stimulate cytotoxic T-cells
Activate B-cells
120
What is the role of cytotoxic T-cells
Kills the specific pathogen via perforin and cytokines
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What does the humoral response involve
B-lymphocytes
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What do B-cells do
Target pathogens by producing antibodies
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How are B-cells activated
Gets antigen from APC then presents it on its own surface membrane
T-helper cells bind to antigen to activate B cells
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What is clonal selection
B cells divide by mitosis to form plasma cells and memory cells
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What are plasma cells and what response are they involved in
Produce antibodies complimentary to antigens
Primary response
126
What are memory cells and what response are they involved in
Upon second infection memory cells rapidly differentiate into plasma B cells to produce antibodies
Secondary immune response- circulate blood in case of reinfection
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What protein structure is antibodies
Quaternary structure
128
What are the 4 chains on antibodies and how are the held together
4 polypeptide chains (2 heavy, 2 light) held together by disulphide bridges
129
What is the variable region
The antigen-binding site
It’s different in every antibody due to their different tertiary structures
130
What region is the same for all antibodies
Constant region
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What region provides the antibody with flexibility
Hinge region
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Wha is agglutination
Antibodies bind to antigens on pathogens causing them to clump together which are they destroyed by phagocytosis
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How do antibodies neutralise toxins
Antibodies bind to toxins and neutralise them
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What do antibodies prevent viruses entering host cells
Antibodies bind to proteins on viruses and stop them attaching to host cells
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What is antigenic variability
Pathogens forming different strains by mutations which result in different antigens
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What happens if you are reinfected to a new strain
Memory cells will not recognise antigen therefore antibodies made last time wont be complimentary, so the body has to start again with primary response so you will get all the symptoms
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Why is it hard to produce vaccines
Antigenic variation
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What is a vaccine
Contains inactive or dead parts of a pathogen to trigger an immune response
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What does one dose of a vaccine induce
A primary response
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What can multiple doses of a vaccine increase
Number of antibodies and memory cells through secondary response
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How are pathogens made harmless
Killing leaving antigens unaffected
Weakening- culturing pathogens
Purified antigens- removed pathogen
Using inactivated toxins
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Why don’t vaccinations fully elimate diseases
Fails to induce immunity in some people
People get infected before enough antibodies are generated
Antigenic variability
Different strains
Objections to vaccines based on ethical grounds
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What are ethical issues with vaccines
Tested on animals first
Humans in clinical trials may be at risk
Some people refuse vaccines over fear of side effects
144
What is herd immunity
A population can be protected from a certain virus if everyone receives the vaccine
145
How is herd immunity achieved
Vaccinating a large amount of the population so enough people are immune meaning it cannot spread
146
What is active immunity
Body making its own antibodies
147
What is passive immunity
Body being given antibodies
148
Example of natural active immunity
Direct exposure to an active pathogen
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Example of artificial active immunity
Vaccinations
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Example of natural passive immunity
Baby gets antibodies through mothers breast milk
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Example of artificial passive immunity
Injected with antibodies from someone else
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Is active immunity long or short term protection and why
Long term because memory cells are produced
153
Is passive immunity long or short term protection and why
Short term protection, only lasts a few months after birth as no memory cells are produced
154
What is monoclonal antibodies
Antibodies produced by plasma cells which are clones of one b cell
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Why are monoclonal antibodies useful
They can be produced outside the body and they are reactive with only one type of antigen
156
What are the main uses of monoclonal antibodies
Target medication to specific cells by attaching drug to antibody
Pregnancy testing
Medical diagnosis by identifying proteins using ELISA test
157
How are monoclonal antibodies involved in pregnancy testing
Monoclonal antibodies are specific to hCG
158
How are monoclonal antibodies involved in diagnosis
Particular antigens are targeted by antibodies to measure levels of that antigen in the body
159
What is the ELISA test used for
To test for presence of any antigen or antibody
160
What is an ELISA test
Where antibodies are attached to an enzyme which produces a coloured substrate
161
What is the structure of HIV
Viral envelope
Capsid
RNA
Attachment proteins
Reverse transcriptase enzymes
162
How does HIV replicate
Attachment proteins on virus bind to receptors on surface of T helper cells
Envelope fuses with T helper cell membrane
Capsid is released into cell where it releases RNA and revers transcriptase enzymes
Reverse transcriptase is used to make DNA from RNA
Newly made DNA moves into nucleus and gets replicated when cell replicates
Viral particles assemble which bud off cell membrane bursting the cell
163
What can HIV lead to
AIDS
164
What are symptoms of AIDS
Infections of respiratory system
Tuberculosis
Chronic diarrhoea
165
How can AIDS be treated
Antiretroviral drugs
Stem cell therapy
PrEP
166
Why are antibiotics ineffective against HIV and viruses
Viruses do not have a cell wall
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What is role of antibodies in producing a positive result in ELISA test
First antibody binds to antigen
Second antibody with enzymes attached is added
Second antibody binds to antigen
Colour changes
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Why is the solution washed in between steps in the ELISA test
To remove excess/unattached antibodies
