Topic 2: Cells Flashcards
(115 cards)
1
Q
What is the structure and function of the nucleus?
A
- Surrounded by a double membrane nuclear envelope
- Membrane contains nuclar pores whcih allows substances to move from nucleus to cytoplasm
- Contains chromosomes which contain protein bound linear DNA
- Have 1 or 2 nucleoi which is the site of RNA production and makes ribosomes
- It is the site of DNA replication and transcription.
2
Q
What is the structure and function of the mitochondria?
A
- Double membrane
- Inner membrane is folded to form cristae
- Matrix is a fluid containing enzymes involved in respiration
- They are the site aerobic respiration and ATP production.
3
Q
What is the structure and function of chloroplasts?
A
-Double membrane
- Has membranes inside called thylakoids, they are stacked up to form stacks called grana
- Stroma is a fluid containing enzymes for photosynthesis.
4
Q
What is the structure and function of the golgi apparatus?
A
- Fluid filled membrane bound flattened sacs forming cisternae.
- Processes, modfies and packages lipids and proteins
- Makes lysosomes
5
Q
What is the structure and function of the golgi vesicles?
A
- Small fluid filled sac in the cytoplasm produced by the golgi apparatus.
- Stores lipids and proteins made by the golgi and transports them out the cell.
6
Q
What is the structure and function of the lysosomes?
A
- Round organelle surrounded by a membrane
- Contains hydrolytic enzymes like lysozymes.
- digests invading cells or break down worn out components of the cells.
7
Q
What is the structure and function of ribosomes?
A
- Small organelles either floating in the cytoplasm or attached to RER.
- Made up of RNA and proteins
- Not surrounded by a membrane
- Site of protein synthesis.
8
Q
What is the structure and function of the rough endoplasmic reticulum (RER)?
A
- Folded membranes called cisternae
- Surface of membranes of membranes called ribosomes
- Folds and processes proteins which have been made at the ribosomes.
9
Q
What is the structure and function of the Smooth endoplasmic reticulum?
A
- Similar to RER bu no ribosomes
- Synthesizes and processes lipids
10
Q
What is the structure and function of the cell wall?
A
- Rigid structure surrounding plants, algae and fungi
- Made of cellulose in plants and algae
- Made of chitin in fungi
- Supports the cell and provides tensile strength and develop turgor pressure.
11
Q
What is the structure and function of the vacuole?
A
- Membrane bound organelle in cytoplasm
- Contains cell sap
- Helps maintain pressure, makes cells turgid to strnegthening them.
- Involved in isolation of unwanted chemicals in the cell.
12
Q
What is the structure and function of the cell membrane?
A
- Made of proteins and lipids
- Regulates the movement of substances in and out the cell
13
Q
What are the key differences between a prokaryotic cell and eukaryotic cell?
A
- Prokaryotes are much smaller and simpler thamn eukaryotes.
- Prokaryotes contain no membrane bound organelles
- Prokaryotes have smaller ribsomes (70s)
- prokaryotes have no nucleus, their dna is floats free in the cytoplasm, the DNA is circular and not associated with proteins.
5.Cell wall is made of murein in prokaryotes. - Some prokaryotes have a flagellum
- Some prokaryotes have plasmids
14
Q
What is the basic structure of a virus?
A
- Unlike bacteria they have no cell membrane, cytoplasm or ribsomes
- Have a protein coat called a capsid
- Capsid has attachment proteins sticking out from it
- Centre contains genetic material.
15
Q
Why is there no treatment for viruses?
A
Replicate inside host cells, hard to destroy them without damaging host cells.
16
Q
What is magnification?
A
How many times bigger an image is then the speciemen being observed.
17
Q
What is resolution?
A
How well a microscope distinguishes between 2 points.
18
Q
What is the purpose of cell fractionation?
A
To isolate different organelles so they can be studied. This enables cell strucutre and function to be studied.
19
Q
What is the first stage in cell fractionation?
A
Homogenisation. The cells are broken open to release the organelles.
20
Q
Why must cells be prepared in a cold isotonic buffered solution?
A
- Cold to reduce enzyme activity which could damage organelles
- isotonic to prevent osmosis which could damage organelles
- Buffered to maintain PH to prevent organelle damage.
21
Q
What is the second stage in cell fractionation?
A
Filtration. Homogenized cell solution is filtered through a gauze to seperate any large cell debris.
22
Q
What is the third stage in cell fractionation?
A
Ultracentrifugation separates the organelles out. Cell fragments are poured into a tube which is out in a centrifuge and is spun at a low speed. The heaviest organelles like nuclei seperate out first and form a pellet at the bottom. The rest of the organelle stays suspended in the fluid above called the supernatant.
The supernatant is spun again at a higher speed and the next heaviest organelle seperates out.
The process is repeated at higher and higher speeds until all the organelles are separated out.
23
Q
What is the order in which organelles seperate out?
A
- Nucleus
- Chloroplasts
- Mitochondria
- Lysosomes
- ER
- Ribsomes
24
Q
What are the principles of a light microscope?
A
A beam of light is condensed to form an image.
25
What are the strengths of a light microscope?
+ Cheap
+ Portable
+ Easy to operate
+ Can view live specimens
+ Can view specimens in colour
26
What are the limitations of a light microscope?
- Can't see organelles smaller than 0.2 micrometers
- Can't see in 3D
- Specimens need to be stained
- maximum magnification of 150 x
- Objects smaller than the wavelength of light appear blury
27
What are the principles of a transmission electron microscope?
Electrons pass through a thin section of a specimen, use electromagnets to focus the beam of electrons. Denser parts absorb more electrons so appear darker
28
What are the strengths of a transmission electron microscope?
+ Give high resolution images so can see internal structures of organelles
+ Maxiumum resolution of 0.5nm, 400x better than an optical microscope.
+ Magnification is up to 500000x
29
What are the limitations of a transmission electron microscope?
- A vacuum environment is needed so specimen must be dead.
- Specimens must be very thin so hard to visualise how the structures are organised
- Don't produce colour images
- Large and expensive
- Staining with heavy metals may introduce artefacts.
30
What are the principles of a scanning electron microscope?
Electrons are scattered along the surface of a specimen to view surface features.
31
What are the advantages of a scanning electron microscope?
+ Produces a 3D image
+ Thin sections are not needed
32
What are the limitations of a scanning electron microscope?
- Has a lower resolution than a transmission electron microscope from less than 1nm to 20nm
- Vacuum is needed
- Specimen must be dead
- large and expensive
- Cant see internal structures
- No colour
33
What are artefacts?
Things visible in a microscope that are not part of the cell or specimen being observed
34
What is the first stage of the cell cycle?
Interphase.
35
What is interphase subdivided into?
1. G1- The cell grows and new organelles are made
2. S- Cell replicates it's DNA
3. G2- Cells keeps growing and proteins needed for cell division are made.
36
What is mitosis for?
Growth and repair in living organisms.
37
Describe the structure of chromosomes?
Made of 2 strands joined in the middle by a centromere. The seperate strands are called a chromatids and 2 strands on the same chromosome are sister chromatids.
38
What happens during prophase?
The chromosomes condense and get shorter and fatter they are now visible. Centrioles move to opposite ends of the cell. Spindle fibres form from the centioles. Nuclear envelope and nucleolus break down.
39
What happens during metaphase?
Chromatids line up along the equator of the cell and become attached to the spindle by the centromere.
40
What happens during anaphase?
Centromeres divide separating each pair of sister chromatids. Spindle contracts pulling chromatids to opposite poles of the cell.
41
What happens during telophase?
Chromatids reach opposite poles and uncoil and become long and thin, now called chromosomes. Nuclear envelope reforms around each set of chromosomes. Dividing of the cytoplasm to form 2 genetically identical diploid daughter cells, this is cytokinesis.
42
How do you calculate mitotic index?
Number of cells undergoing mitosis / total number of cells x100
43
What is a cancer?
Uncontrolled cell division whcih can forma cluster of cells called a tumour.
44
What is the difference between a benign tumor and a malignant tumour?
Benign tumors are encapsulated and non invasive whereas malignant tumours are notcapsulated and invasive and can undergo metastasis.
45
What does chemotherapy do?
Interferes with G1. Prevents the synthesis of enzymes needed for dna replication, so the cell is unable to enter the S phase disrupting the cell cycle and forces the cell to kill itself.
46
What does radiation do?
Interferes with the S phase. Radiation and some drugs damage dna. At several points in the cell cycle the dna is checked for damage, if severe damage is detected the cell with kill itself.
47
What happens in binary fission?
1. The circular DNA and plasmids replicate. The main DNA loop is replicated once but plasmids can be replicated lots of times.
2. Cells gets bigger and DNA loops move to opposite poles of the cell.
3. Cytoplasm begins to divide and new cell wall starts to form.
4. Cytoplasm divides and 2 daughter cells are produced, each cell has one copy of the circular DNA but can have a variable number of plasmids.
48
How do viruses replicate?
Viruses are non living so don't undergo cell division. They inject their dna or rna into a host cell, this cell is then hijacked and replicates the virus particles. Viruses attach to the host cell surface using their attchment proteins to bind to complementary receptor proteins on the host cell.
49
Why is the cell membrane known as the fluid mosaic model?
The phospholipid bilayer is fluid because the phospholipids are constantly moving. Proteins are scattered around the bilayer like tiles in a mosaic.
50
What is the role of phospholipids in the cell membrane?
The heads are hydrophillic and the tails are hydrphobic, these molecules automatically arrange themselves into a bilayer. The centre of the bilayer is hydrophobic so the membrane doesn't allow water soluable to diffuse through it.
51
What is the role of cholestrol in the cell membrane?
Gives the membrane stability. Binds to the hydrophobic tails causing them to pack closer together.This restricts the movement of phospholipids making the membrane less fluid and more rigid at high temperatures which prevents fluids leaking out.
52
What is the role of extrinsic proteins?
Function as enzymes and catalyse reactions in the cell.
Some have a carbohydrate attached forming glycoproteins.
53
What is the role of glycoproteins and glycolipids?
Cell regognition as receptors
54
What do channel proteins do?
Form tubes that fill with water to allow water soluable ions to diffuse.
55
What do carrier proteins do?
Allow molecules to bind with these larger molecules cause the protein to change shape and transport them to the otehr side of the membrane.
56
What is diffusion?
The net movement of particles from an area of high concentration to an area of low concentration until they are evenly distributed. A passive process not requiring ATP.
57
What are the factors affecting rate of diffusion?
1. Concentration gradient
2. Thickness of the exchange surface
3. Surface area
4. Temperature
58
What do the molecules have to be to diffuse across the membrane in simple diffusion?
Lipid soluable and small. so they can fit through gaps between phospholipids and dissolve in the hydrophobic bilayer.
59
What is facilitated diffusion?
Passive movement of molecules from low to high concentration but involving carrier proteins and channel proteins.
60
What kinds of molecules require facilitated diffusion and why?
Large and charged particles like ions and polar moelcules as they are water soluable and the centre of the bilayer is hydrophobic.
61
How do carrier proteins work?
A large molecule attaches to a carrier protein.
The protein changes shape
This releases the molecule on the opposite side of the membrane
62
How to channel proteins work?
Form pores in the membrane for charged particles to diffuse down, form water filled hydrphillic channels they are shaped for a specific charged particle.
63
What are the factors affecting the rate of facilitated diffusion?
1. Concentration gradient
2. Number of channel and carrier proteins available.
64
What is osmosis?
Movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane.
65
What is isotonic?
When the water potential inside and outside the cell are equal so there is no net movement of water.
66
What is hypotonic?
When the water potential outside of the cell is greater than inside so there is a net movement of water into the cell.
67
What is hypertonic?
When the water potential outside of the cell is lower than inside the cell causing a net movement of water out of the cell.
68
What are the factors affecting the rate of osmosis?
1. The water potential gradient
2. Thickness of the exchange surface
3. Surface area of the exchange surface
69
What is active transport?
Movement of substances from low to high concentration against the concentration gradient. Involves metabolic energy and carrier proteins.
70
What happens in active transport?
1. A molecule binds to a receptor complementary in shape on the carrier protein.
2. ATP binds to the protein and is hydrolysed into ADP + Pi
3. Causes the carrier protein to change shape and releases the molecule on the other side.
4. The phosphate ion is released and the protein reverts back to its original shape.
71
What is co transport?
Movement of a substance against it's concentration gradient is coupeled with the movement of a substance down it's concentration gradient.
71
How is co transport involved in the absorbtion of glucose in the small intestine?
1. Sodium ions are actively transported out of the epithelial cells
2. reduces the sodium ion concentration in the cells.
3. Sodium ions can then diffuse from the lumen into the cell down their concentration gradient.
4. Sodium ions diffuse through a co transporter so either glucose or amino acids also attach and are transported into the cell against their concentration gradient.
5. Glucose then moves by facilitated diffusion down its concentration gradient into the blood.
72
What is an antigen?
Proteins on a cells surface which generate an immune response when detected by the body.
73
What do antigens allow the immune system to identify?
1. Pathogens
2. Abnormal body cells
3. Toxins
4. Cells from other individuals of the same species.
74
What is antigenetic variation?
If a mutation occurs in the gene which codes of the antigen then the shape of the antigen can change. This means that when you are infected for the second time the memory cells produced from the first infection will not recognise the different antigens, so the immune system has to start from scratch and carry out a primary response for these new antigens.
75
What are the steps of phagocytosis?
1. A phagocyte recognises the forgein antigens on a pathogen
2. Cytoplasm moves round the pathogen and engulfs it.
3. Pathogen is contained in a phagocytic vacuole in the cytoplasm.
4. A lysosome fuses with the vesicle and the pathogen is broken down by lysozymes
5. The phagocyte then presents the pathogens antigens to active other immune system cells.
76
What is the cellular/cell mediated response?
The response involving T cells and the other immune system cells that they interact with.
77
Where do T cells mature?
In the thymus gland.
78
What are antigen presenting cells?
Any cell that presents a non self antigen on their surface.
79
How does the cell mediated response work?
1. Once a pathogen has been engulfed and destroyed by a phagocyte the antigens are displayed on the cell surface.
2. Helper T cells have receptor proteins on their surface which attach to antigens on the APC.
3. This activates the helper t cells to divide by mitosis and make lots of clones
4. These cells then differentiate into different cells. Some remain and helper T cells and activate B lymphocytes, some stimulate phagocytes to carry out more phagocytosis, some become memory cells for that shape antigen and some become cytotoxic T cells.
80
What do cytotoxic T cells do?
Destroy abnormal or infected cells. They release a protein called perforin which embeds in the cell surface membrane so any substances can enter or leave the cell, this causes the cell to die.
81
Where do B cells mature?
In the bone marrow
82
What is the humoral response?
The response involving B cells and antobodies
83
How are B cells activated?
1. Antigens in the blood collide with their complementary antibody on a B cell. The B cell takes in the antigen by endocytosis and presents the antigens on its surface
2. When the B cell collides with a helper T cell this activates the B cell to undergo clonal expansion and clonal selection
3. B cells undergo mitosis to make lots of clones which then differentiate into plasma cells or memory B cells.
84
What do the plasma cells do?
Make antibodies complementary in shape to the particular antigen
85
What do the B memory cells do?
Divide rapidly into plasma cells when reinfected with the same pathogen to make a large number of antibodies rapidly.
86
What is the primary immune response?
Occurs when you are first infected with a pathogen. Slow becuase there aren't many B cells to make the antibodies needed. T and B cells both produce memory cells which remain in the body for a long time. Memory T cells remember the antigen and memory B cells remember the antibody needed.
87
What is the secondary immune response?
If the same pathogen re enters the body the immune system will a produce a quicker stronger response. Mmemory B cells are activated and divide into plasma cells that produce the rihht antibody to the antigen. Don't usually show symptoms.
88
What is an antibody?
Proteins produced by the immune system in response to foreign substances.
89
Describe the structure of an antibody.
- has a quaternary structure made of 4 polypeptide chains
- Variable regions are specific to a particular antigen which binds to it. Has a unique tertiary structure.
- Constant region is the same in all antibodies.
- Long chains are heavy chains
- Short chains are light chains
90
What is agglutination?
An antibody has 2 binding sites so can bind to 2 pathogens at the same time. So the pathogens get clumped together.
91
What is active immunity?
When your immune system makes it's own antibodies after being stimulated by an antigen. Takes a while for protection to develop but it is long term.
92
What is natural active immunity?
When you become immune after catching a disease.
93
What is artificial active immunity?
When you become immune after receiving a vaccination
94
What is passive immunity?
Antibodies are introduced into the body. No plasma cells or memory cells are made. Protection is immediate but short term.
e.g breast milk.
95
What is natural passive immunity?
When a bbay becomes immune due to the antibodies it recieves through it's mother through the placenta or breast milk.
96
What is artificial passive immunity?
When you become immune by being injected with antibodies from someone else.
97
How do vaccines work?
Dead or attenuated pathogen is injected into the body. This activates the B cells to undergo clonal expansion and selection. It the divides by mitosis and differentiates into plasma cells and memory B cells. Plasma cells make antibodies which stay in the blood for a very long time.
98
What is the concept of herd immunity?
If enough of the population are vaccinated the pathogen cannot spread easily throughout the population. so provides protection for those who are not vaccinated.
99
What are some ethical issues surrounding vaccines?
1. Animal testing
2. Side effects
3. Playing God
4. Epidemics
100
Describe the structure of HIV
1. Core containing genetic material (RNA) and the enzyme reverse transcriptase which is needed for viral replication.
2. Capsid which is an outer protein coat
3. Envelope is an extra outer layer made of a membrane taken from the hosts cell membrane.
4. Protein attachments to enable the virus to attach to the host helper T cell.
101
How does HIV replicate in helper T cells?
1. Attachment protein attaches to a CD4 protein on the helper T cell.
2. capsid fuses with the helper T cell membrane and releases the enzymes and RNA into the cell.
3. Reverse transcriptase makes a complementary DNA strand from the viral RNA template.
4. The double stranded DNA moves into the helper T cell nucleus
5. Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
6. The viral proteins are assembled into new viruses which bud from the cell and go on to infect other cells.
102
When would we say a person with HIV has developed AIDS?
When the number of helper T cells in the body reach a critically low level.
103
What is the latency phase?
Where HIV replication is at a low level so the person won't experience any symptoms.
104
Why are antibiotics ineffective against viruses?
Antibiotics kill bacteria by targetting bacterial enzymes and ribosomes., antibiotics are only designed to target the bacterial ones so they don't damage human cells. Viruses don't have their own enzymes or ribsomes so use ones in host cells so becuase viruses use human enzymes and ribsomes to replicate antibiotics can't inhibit them as they don't target human processes.
105
How can HIV be controlled?
- antiviral drugs slow down progression
- Protected sexual intercourse
106
How does HIV cause symptoms of AIDS?
HIV destroys the helper t cells so unable to produce an adequate immune response to other pathogens so if left vulnerable to infections.
107
What are monoclonal antobodies?
Antibodies produced from a single group of genetically identical B cells.
108
How are monoclonal antibodies used in cancer treatment?
Monoclonal antibodies can be created with binding sites complementary in shape to antigens on the cancer cells surface. A drug is attached to the other end of the antibody. When the antibodies come into contact with the cancer cells they will bind to the antigens so the drug will only accumulate where the cancer cells are so don't cause harm to other body cells.
109
How are monoclonal antibodies used in pregnancy tests?
1. The application area contians antibodies that are complementary to the hCG protein, bound to a blue coloured bead.
2. When urine is applied to the application area, any hCG will bind to the antibody on the beads forming an antigen antibody complex.
3.The urine moves up the stick to the test strip carrying any beads with it.
4. The test strip contains immobilised antibodies to hCG
5. If hCG is present the test strip turns blue becuase the immoblised antibody binds to hCG - concentrating the hCG antibody with the blue beads attached.
If no hCG is present the beads will pass through the test area without binding to anything so it won't go blue.
110
What is an elisa test?
Allows you to see if a patient has any antibodies to a certain antigen or vice versa. Used to test for pathogenic infections and allergies.
111
How does an elisa test work?
An antibody is used which has an enzyme attached to it, this enzyme can react with a substrate to produce a coloured product, this causes the solution in the reaction vessel to change colour. If there is a colour change its shows that the antigen or antibody is present.
112
What happens in a direct elisa test?
- Uses a single antibody that is complementary to the antigen testing for
- Antigens from a patient sample are bound to the inside of a well plate.
- A detection antibody( with an attached enzyme ) that is complementary to the antigen of interest is added.
- If the antigen of interest is present it will be immoblised on the surface of the well and the detection antibody will bind to it.
- The well is then washed to remove any unbound antibody and a substrate solution is added
- If the detection antibody is present the enzyme reacts with the substrate to give a colour change, this is a positive result for presence of the antigen.
113
What happens in an indirect elisa test (HIV example)
1. HIV antigen is bound to the bottom of a well.
2. Sample of the patients blood plasma which may contain several antibodies is added to the well. If there are any HIV specific antibodies in the plasma they will bind to the HIV antigen. The well is then washed to remove unbound antibodies
3. A secondary antibody with a specific enzyme attached is added to the well, this can bind to the HIV specific antibody. The well is washed out again to remove any unbound secondary antibody.
4. Solution is added to the well which contains a substrate which reacts with the enzyme attched to the secondary antibody and produces a coloured product.
If the solution changes colour it shows that the patient has HIV specific antibodies in the blood and has HIV.
114
What are the ethical issues surrounding monoclonal antibodies?
Many people disagree with the fact animals are used to produce the cells from which monoclonal antibodies are produced,
