3.2 Cells Flashcards
1
Q
Cell membrane structure
A
Phospholipid bilayer with embedded intrinsic & extrinsic proteins
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2
Q
Cell membrane function
A
- Selectively permeable barrier
- controls passage of substances in and out the cell
- barrier between internal and external cell environments
3
Q
Nucleus structure
A
- Nuclear pores, nucleolus, DNA and nuclear envelope
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4
Q
Nucleus function
A
- Site of transcription & pre-mRNA splicing – mRNA production
- site of DNA replication
- nucleolus makes ribosomes
- nuclear pore allows movement of substances to/from cytoplasm
5
Q
Mitochondria structure
A
- Double membrane with inner membrane folded into cristae
- 70S ribosomes in matrix
- small, circular DNA
- enzymes in matrix
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6
Q
Mitochondria function
A
- Site of aerobic respiration
- produces ATP
7
Q
Chloroplast structure
A
- Thylakoid membranes stacked to form grana, linked by lamellae
- stroma contains enzymes
- contains starch granules, small circular DNA and 70S ribosomes
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8
Q
Chloroplast function
A
- Chlorophyll absorbs light for photosynthesis to produce organic molecules (glucose)
9
Q
Organisms containing
chloroplasts
A
- Plants
- Algae
10
Q
Golgi apparatus stucture
A
- Fluid-filled, membrane-bound sacs (horseshoe shaped)
- vesicles at edge
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11
Q
Golgi apparatus function
A
- Modifies proteins received from RER
- packages them into vesicles to transport to cell membrane for exocytosis
- makes lysosomes
12
Q
Lysosome structure
A
- Type of Golgi vesicle containing digestive enzymes
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13
Q
Lysosome function
A
- Contains digestive enzymes
- e.g. lysozymes to hydrolyse pathogens/cell waste products
14
Q
Rough endoplasmic reticulum function
A
- Site of protein synthesis
- folds polypeptides to secondary & tertiary structures
- packaging into vesicles to transport to Golgi
15
Q
Smooth endoplasmic reticulum function
A
- Synthesises and processes lipids
16
Q
Cell wall function
A
- Provides structural strength, rigidity and support to cell
- helps resist osmotic pressures
17
Q
Ribosome structure
A
- Small and large subunit
- made of protein and rRNA
- free floating in cytoplasm & bound to RER
- 70S in prokaryotes, mitochondria and chloroplasts
- 80S in eukaryotes
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18
Q
Ribosome function
A
- Site of translation in protein synthesis
19
Q
Rough endoplasmic reticulum structure
A
- System of membranes with bound ribosomes
- continuous with nucleus
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20
Q
Smooth endoplasmic reticulum structure
A
- System of membranes with no bound ribosomes
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21
Q
Cell wall structure
A
- In plant, fungal and bacterial cells
- plants – made of microfibrils of cellulose
- fungi – made of chitin
- bacteria – murein
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22
Q
Cell vacuole structure
A
- Fluid-filled
- surrounded by a single membrane called a tonoplast
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23
Q
Contrast prokaryotic & eukaryotic cells
A
- Prokaryotic cells are smaller
- prokaryotes have no membrane bound organelles
- prokaryotes have smaller 70S ribosomes
- prokaryotes have no nucleus – circular DNA not associated with histones
- prokaryotic cell wall made of murein instead of cellulose/chitin
24
Q
Occasional features of prokaryotes
A
- Plasmids – loops of DNA
- capsule surrounding cell wall – helps agglutination + adds protection
- flagella for movement
25
Q
Cell vacuole function
A
- Makes cells turgid – structural support
- temporary store of sugars, amino acids
- coloured pigments attract pollinators
26
Q
Protein carriers
A
- Bind with a molecule, e.g. glucose, which causes a change in the shape of the protein
- this change in shape enables the molecule to be released to the other side of the membrane
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27
Q
Protein channels
A
- Tubes filled with water enabling water-soluble ions to pass through the membrane
- selective
- channel proteins only open in the presence of certain ions when they bind to the protein
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28
Q
Features of viruses
A
- Non-living and acellular
- contain genetic material, capsid and attachment proteins
- some (HIV) contain a lipid envelope + enzymes (reverse transcriptase)
29
Q
3 types of microscopes
A
- Optical (light) microscopes
- Scanning electron microscopes (SEM)
- Transmission electron microscopes (TEM)
30
Q
Magnification
A
- How many times larger the image is compared to the object
- calculated by equation:
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31
Q
Resolution
A
- The minimum distance between two objects in which they can still be viewed as separate
- determined by wavelength of light (for optical microscopes) or electrons (for electron microcopes)
32
Q
Optical microscopes
A
- Beam of light used to create image
- glass lens used for focusing
- 2D coloured image produced
33
Q
Evaluate optical microscopes
A
- Poorer resolution as long wavelength of light – small organelles not visible
- lower magnification
- can view living samples
- simple staining method
- vaccum not required
34
Q
Transmission electron microscopes
A
- Beam of electrons passes through the sample used to create an image
- focused using electromagnets
- 2D, black & white image produced
- can see internal ultrastructure of cell
- structures absorb electrons and appear dark
35
Q
Evaluation TEMs
A
- Highest resolving power
- high magnification
- extremely thin specimens required
- complex staining method
- specimen must be dead
- vaccum required
36
Q
Scanning electron microscopes
A
- Beam of electrons pass across sample used to create image
- focused using electromagnets
- 3D, black and white image produced
- electrons scattered across specimen producing image
37
Q
Evaluation SEMs
A
- High resolving power
- high magnification
- thick specimens usable
- complex staining method
- specimen must be dead
- vaccum required
38
Q
Why calibrate eyepiece graticule?
A
- Calibration of the eyepiece is required each time the objective lens is changed
- calibrate to work out the distance between each division at that magnification
39
Q
Purpose of cell fractionation
A
- Break open cells & remove cell debris
- so organelles can be studied
40
Q
Homogenisation
A
- Process by which cells are broken open so organelles are free to be separated
- done using homogeniser (blender)
41
Q
Homogenisation conditions
A
- Cold reduces enzyme activity preventing organelle digestion
- Isotonic prevents movement of water by osmosis – no bursting/shrivelling of organelles
- Buffered resists pH changes preventing organelle + enzyme damage
42
Q
Ultra-centrifugation
A
- Homogenate solution filtered to remove cell debris
- solution placed in a centrifuge which spins at a low speed initially
- then increasingly faster speeds to separate organelles according to their density
43
Q
Differential centrifugation
A
- Supernatant first out (spun at lowest speed) is most dense = nuclei
- spun at higher speeds
- chloroplasts → mitochondria → lysosomes → RER/SER → ribosomes (least dense)
44
Q
Binary Fission
A
- Involves circular DNA & plasmids replicating
- cytokinesis creates two daughter nuclei
- each daughter cell has one copy of circular DNA and a variable number of plasmids
45
Q
Cell cycle
A
- Interphase (G1, S, G2)
- nuclear division – mitosis or meiosis
- cytokinesis
46
Q
Interphase
A
- Longest stage in the cell cycle
- when DNA replicates (S-phase) and organelles duplicate while cell grows (G1 & G2-phase)
- DNA replicates and appears as two sister chromatids held by centromere
47
Q
Mitosis
A
- One round of cell division
- two diploid, genetically identical daughter cells
- growth and repair (e.g. clonal expansion)
- comprised of prophase, metaphase, anaphase and telophase
48
Q
Prophase
A
- Chromosomes condense and become visible
- nuclear envelope disintegrates
- in animals – centrioles separate & spindle fibre structure forms
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49
Q
Metaphase
A
- Chromosomes align along equator of cell
- spindle fibres released from poles now attach to centromere and chromatid
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50
Q
Anaphase
A
- Spindle fibre contracts (using ATP) to pull chromatids, centromere first, towards opposite poles of cell
- centromere divides in two
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51
Q
Telophase
A
- Chromosomes at each pole become longer and thinner again
- spindle fibres disintegrate + nucleus reforms
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52
Q
Mitotic index
A
- Used to determine proportion of cells undergoing mitosis
- Calculated as a percentage OR decimal
- x100 for percentage
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53
Q
Fluid mosaic model
A
- Describes the lateral movement of membranes
- with scattered embedded intrinsic and extrinsic proteins
- membrane contains glycoproteins, glycolipids, phospholipids and cholesterol
54
Q
Phospholipids in membranes
A
- Phospholipids align as a bilayer
- hydrophilic heads are attracted to water
- hydrophobic tails repelled by water
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55
Q
Cholesterol
A
- Present in eukaryotic organisms to restrict lateral movement of the membranes
- adds rigidity to membrane – resistant to high temperatures & prevents water + dissolved ions leaking out
56
Q
Selectively permeable membrane
A
- Molecules must have specific properties to pass through plasma membrane:
- lipid soluble (hormones e.g. oestrogen)
- very small molecules
- non-polar molecules (oxygen)
57
Q
Simple diffusion
A
- Net movement of molecules from an area of higher concentration to an area of lower concentration
- until equilibrium is reached
- passive
58
Q
Facilitated diffusion
A
- Passive process using protein channels/carriers
- down the concentration gradient
- used for ions and polar molecules e.g. sodium ions
- and large molecules e.g. glucose
59
Q
Osmosis
A
- Net movement of water
- from an area of higher water potential to an area of lower (more negative) water potential
- across a partially permeable membrane
60
Q
Water potential
A
- The pressure created by water molecules
- measured in kPa and represented by symbol ψ
- pure water has a water potential of 0kPa
- the more negative the water potential, the more solute must be dissolved
61
Q
Hypertonic solution
A
- When the water potential of a solution is more negative than the cell
- water moves out of the cell by osmosis
- both animal and plant cells will shrink and shrivel
62
Q
Hypotonic solution
A
- When the water potential of a solution is more positive (closer to zero) than the cell
- water moves into the cell by osmosis
- animal cells will lyse (burst)
- plant cells will become turgid
63
Q
Isotonic
A
- When the water potential of the surrounding solution is the same as the water potential inside the cell
- no net movement in water
- cells would remain the same mass
64
Q
Active transport
A
- The movement of ions and molecules from an area of lower concentration to an area of higher concentration using ATP and carrier proteins
- carrier proteins act as selective pumps to move substances
65
Q
Role of carrier protein in active transport
A
- When molecules bind to the receptor – ATP will bind to protein on inside of membrane and is hydrolysed to ATP/Pi
- protein changes shape and opens inside membrane
66
Q
Co-transport
A
- The movement of two substances across a membrane together, when one is unable to cross the membrane itself
- involves a cotransport protein
- involves active transport
- e.g. absorption of glucose/amino acids from lumen of intestines
67
Q
Molecules lymphocytes identify
A
- Pathogens (bacteria, fungi, viruses)
- cells from other organisms of same species (transplants)
- abnormal body cells (tumour cells)
- toxins (released from bacteria)
68
Q
Antigens
A
- Proteins on the cell-surface membrane
- trigger an immune response when detected by lymphocytes
69
Q
Antigenic variability
A
- When pathogenic DNA mutates causing a change in shape of antigen
- previous immunity is no longer effective as memory cells don’t recognise new shape of antigen
- specific antibody no longer binds to new antigen
70
Q
Physical barriers
A
- Anatomical barriers to pathogens:
- skin
- stomach acid
- lysozymes in tears
71
Q
Phagocytes
A
- Non-specific immune response
- phagocytes become antigen-presenting cells after destroying pathogen
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72
Q
T lymphocytes
A
- Made in bone marrow and mature in thymus gland
- involved in cell-mediated immune response
- respond to antigen-presenting cells
73
Q
Antigen-presenting cells
A
- Any cell that presents a non-self antigen on their surface:
- infected body cells
- macrophage after phagocytosis
- cells of transplanted organ
- cancer cells
74
Q
Role of T helper cells
A
- Have receptors on their surface that attach to antigens on APCs
- become activated – clonal selection
75
Q
Role of cloned T helper cells
A
- Some remain as helper T cells & activate B lymphocytes
- stimulate macrophages for phagocytosis
- become memory cells for that shaped antigen
- become cytotoxic killer T cells
76
Q
Cytotoxic T cells
A
- Destroy abnormal/infected cells by releasing perforin
- so that any substances can enter or leave the cell and this causes cell death
77
Q
B lymphocytes
A
- Made in bone marrow and mature in bone marrow
- involved in humoral immune response
- involves antibodies
78
Q
Humoral response
A
- APC activates B cell
- B cell undergoes clonal selection and expansion – rapid division by mitosis
- differentiate into plasma cells/memory B cells
- plasma cells make antibodies
79
Q
B memory cells
A
- derived from B lymphocytes
- remember specific antibody for particular antigen
- will rapidly divide by mitosis and differentiate in plasma cells upon secondary encounter
- resulting in large numbers of antibodies rapidly
80
Q
Antibodies
A
- Quaternary structure proteins made of four polypeptide chains
- different shaped binding site = variable region
- complementary to a specific antigen
81
Q
Antibody structure
A
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82
Q
Agglutination
A
- Antibodies have two binding sites and are flexible – clumps pathogens together
- makes it easier for phagocytes to locate and destroy pathogen
83
Q
Passive immunity
A
- Antibodies introduced into body
- plasma and memory cells not made as no interaction with antigen
- short-term immunity
- fast acting
84
Q
Active immunity
A
- Immunity created by own immune system – antibodies made
- exposure to antigen
- plasma and memory cells made
- long term immunity
- slower acting
85
Q
Natural active immunity
A
- After direct contact with pathogen through infection
- body creates antibodies and memory cells
86
Q
Artificial active immunity
A
- Creation of antibodies and memory cells following introduction of an attenuated pathogen or antigens
- vaccination
87
Q
Vaccinations
A
- Small amounts of dead or attenuated pathogens injected/ingested
- humoral response activated
- memory cells are able to divide rapidly into plasma cells when re-infected
88
Q
Primary Vs Secondary response
A
- Primary = first exposure to the pathogen
- longer time for plasma cell secretion & memory cell production
- for the secondary response, memory cells divide rapidly into plasma cells
- so a large number of antibodies made rapidly upon reinfection
89
Q
Herd immunity
A
- When enough of the population is vaccinated so pathogen is not transmitted and spread easily
- provides protection for those without vaccine
90
Q
Monoclonal antibodies
A
- A single type of antibody that can be isolated and cloned
- antibodies that are identical – from one type of B lymphocyte
- complementary to only one antigen
91
Q
Uses of monoclonal antibodies
A
- Medical treatment – targeting drugs by attaching antibody complementary to tumour cell antigen
- medical diagnosis – pregnancy tests
92
Q
Pregnancy test
A
- ELISA test which uses 3 monoclonal antibodies and enzymes to test for hCG
93
Q
Purpose of ELISA test
A
- Detect the presence and quantity of an antigen
- used for medical diagnosis e.g. HIV
94
Q
Ethical issues with monoclonal antibodies
A
- Requires mice to produce antibodies and tumour cells
- requires a full cost-benefit analysis
95
Q
HIV structure
A
- Core = RNA and reverse transcriptase
- capsid = protein coat
- lipid envelope taken from hosts cell membrane
- attachment proteins so it can attach to Helper T cells
96
Q
HIV replication
A
- Attaches to CD4 receptor on helper T cells
- protein fuses with membrane allowing RNA + enzymes to enter
- reverse transcriptase makes DNA copy and this is inserted into nucleus
- nucleus synthesises viral proteins
97
Q
Auto Immunodeficiency Syndrome (AIDs)
A
- When HIV has destroyed too many T helper cells, host is unable to produce adequate immune response to other pathogens
- host susceptible to opportunistic infections
98
Q
Role of antibodies in ELISA
A
- First antibody added is complementary to antigen in well –attaches
- second antibody with enzyme added which attaches to first antibody as complementary
- when substrate solution added enzyme can produce colour change
99
Q
Why vaccines may be unsafe
A
- Inactive virus may become active – viral transformation
- non-pathogenic virus can mutate and harm cells
- side effects of immune response
- people may test positive for disease
100
Q
Why are antibiotics ineffective against viruses?
A
- Viruses are inside host cells where antibiotics cannot reach
- antibiotics affect parts of bacteria that viruses do not have (e.g. the cell wall)
101
Q
Why do you wash well in ELISA
A
- Removes unbound 2nd antibodies
- otherwise enzyme may be present → colour change → false positive
102
Q
Pathogens
A
- Microorganisms that cause a disease
- by releasing toxins or killing cells/tissues
103
Q
Cytokinesis
A
- Final stage in the cell cycle
- when the cytoplasm splits in two
- creates two new cells
104
Q
Uncontrolled mitosis
A
- Uncontrolled cell division can lead to the formation of tumours and of cancers
- many cancer treatments are directed at controlling the rate of cell division
105
Q
Viral replication
A
- Following injection of their nucleic acid
- the infected host cell replicates the virus particles
106
Q
Cell adaptations for rapid transport across membranes?
A
- Increase in surface area or membrane
- increase in the number of protein channels and carrier molecules in the membranes
107
Q
Antigen-antibody complex
A
- When a complementary antibody binds to an antigen
- this clumps pathogens together (agglutination)
