Topic 2 - Cells Flashcards
1
Q
Nucleus Structure
A
Nuclear envelope - double membrane
Nuclear pores
Nucleoplasm - granular, jelly-like material
Chromosomes - protein-bound, linear DNA
Nucleolus - smaller, inside, site of rRNA production and makes ribosomes
2
Q
Nucleus Function
A
Site of DNA replication and transcription (making mRNA)
Contains genetic code for each cell
3
Q
Endoplasmic Reticulum Structure
A
Rough and Smooth both have folded membranes called cisternae
RER have ribosomes on cisternae
4
Q
Endoplasmic Reticulum Function
A
RER - Protein Synthesis
SER - Synthesise and store lipids and carbs
5
Q
Golgi Apparatus Structure
A
Folded membranes making cisternae
Secretory vesicles pinch off from the cisternae
6
Q
Golgi Apparatus Function
A
Add carbs to proteins to form glycoproteins
Transport, modify and store lipids
Form lysosomes
Produce secretory enzymes
7
Q
Lysosomes Structure
A
Bags of digestive enzymes - can contain 50 different enzymes
8
Q
Lysosomes Function
A
Hydrolyse phagocytic cells
Autolysis - completely break down dead cells
Exocytosis - release enzymes to outside of cell to destroy material
9
Q
Mitochondria Function
A
Aerobic respiration
ATP production
DNA to code for enzymes needed for respiration
10
Q
Ribosomes Structure
A
Small, made up of two sub-units of protein and rRNA
80s - large ribosomes (eukaryotic cells, 25nm)
70s - smaller ribosomes (prokaryotic cells, mitochondria, chloroplasts)
11
Q
Ribosomes Function
A
Site of protein synthesis
12
Q
Chloroplast Structure
A
Surrounded by double membrane
Contains thylakoids (folded membranes embedded with pigment)
Fluid filled Stroma contains enzymes for photosynthesis
13
Q
Chloroplast function
A
Photosynthesis
14
Q
Cell Wall Structure
A
Plants - made of microfibrils of the cellulose polymer
Fungi - made of chitin, a nitrogen-containing polysaccharide
15
Q
Cell wall Function
A
Structural strength to the cell
16
Q
Plasma membrane structure
A
In all cells
Phospholipid bilayer - molecules embedded within and attached on the outside (proteins, carbs, cholesterol)
17
Q
Prokaryotic Cells compared to Eukaryotic Cells
A
Pro cells much smaller
Pro have no membrane-bound organelles
Pro have smaller ribosomes
Pro have no nucleus
Pro have cell wall made of murein
Pro may also contain plasmids, capsule and flagella
18
Q
Membrane Bound Organelles
A
Pro cells - mesosomes are in-foldings of the cell membrane that provide a large SA for the attachment of the enzymes involved in respiration
Euk cells - mitochondria, chloroplasts, ER, Golgi
19
Q
Mitochondria Structure
A
Double membrane
Inner membrane (cristae)
Fluid centre (mitochondrial matrix)
Loop of mitochondria DNA
20
Q
Vacuole Structure
A
- filled with fluid surrounded by single membrane called a tonoplast
21
Q
Vacuole Function
A
- make cells turgid and therefore provide support
- temporary store of sugars and amino acids
- pigments may colour petals to attract pollinators
22
Q
Viruses
A
Acellular and non-living
Replicate inside of host cells - difficult to destroy without harming host cell
23
Q
Viruses Structure
A
Genetic material
Capsid
Attachment protein
24
Q
Types of Microscopes
A
Optical (light) microscope - resolution determined by wavelength of light
Transmission electron microscope and Scanning electron microscope - resolution determined by wavelength of beam of electrons
25
Magnification
How many times larger image is compared to object
26
Resolution
Minimum distance between two objects in which they are still viewed as separate
27
Optical microscope
Beam of light condensed to create image
Poorer resolution due to longer wavelength
Lower magnification
Colour images
Can view living samples
28
Electron microscope
Beam of electrons condensed to create image. Electromagnets condenses beam.
Higher resolution due to shorter wavelength
Higher magnification
Black and white images
Must be non-living
29
Image Size, Actual Size and Mag Equation
Image Size = Actual Size x Mag (I=AM)
Actual Size = Image Size/Mag (A=I/M)
Mag = Image Size/Actual size (M=I/A)
30
Eye Piece Graticule
Inside optical microscope
Scale on glass disc
Measures size of objects under microscope
31
Cell Fractionation Key points
Isolate different organelles to be studied
Enables individual organelle structure and function to be studied
Cells broken open to release contents and organelles then separated
32
Why must Cells be prepared in cold, isotonic and buffered solution
Cold - reduce enzyme activity
Isotonic - same water potential to prevent osmosis as it could lead to cell shrivel or burst
Buffered - solution has pH buffer to prevent damage to organelles
33
Two steps of cell fractionation
Homogenisation
Ultracentrifugation
34
Homogenisation
Cells broken open (homogenised) in blender. Blended in cold, isotonic and buffered solution.
36
Ultracentrifugation
Filtered solution spun at different speeds in centrifuge
Organelles separate according to their densities.
37
Differential centrifugation
Low speed to high speeds
Each time supernatant (liquid) is removed, leave behind pellet of organelle
1. Nucleus 2. Chloroplasts (if plant tissue) 3. Mitochondria 4. Lysosomes 5. ER 6. Ribosomes
38
Stages of cell cycle
Interphase
Nuclear division (mitosis or meiosis)
Cytokinesis
39
Cell Division in eukaryotes, prokaryotes and viruses
Eukaryotic cells enter cell cycle and divide by mitosis or meiosis
Prokaryotic cells replicate by binary fission
Viruses don’t divide - non-living
Viruses replicate inside host cells - inject their nucleic acids into cell to replicate virus particles
39
Interphase
Longest stage
Organelles double, cell grows and then DNA replicates
40
Nuclear Division
Mitosis - two identical diploid cells, for growth and repair
Meiosis - four genetically different haploid cells, gametes
41
Cytokinesis
Final stage
Division of cytoplasm to create new cells
42
Mitosis stages
Prophase
Metaphase
Anaphase
Telophase
43
Mitosis key points
One round of division
Genetically identical cells made
Diploid cells made
Growth and repair
44
Prophase
- chromosomes condense and become visible
- centrioles create spindle fibres - released from both poles of cell to create spindle apparatus
- nucleolus disappears
45
Metaphase
- chromosomes align along equator of cell
- spindle fibres attach to centromere and chromatid
46
Anaphase
- spindle fibres retract and pull the centromere and chromatids to opposite poles
- centromere divides in two and individual chromatids pulled it each opposite pole - separated chromatids now are chromosomes
- stage requires energy (ATP) provided by respiration in mitochondria
47
Telophase and Cytokinesis
Telophase:
- chromosomes now at each pole of cell and become longer and thinner again
- spindle fibres disintegrate and nucleus starts to reform
Cytokinesis:
- cytoplasm splits in two ago create two new genetically identical cells
48
Mitotic Index Equation
Number of cells in mitosis/total number of cells x 100
49
Binary Fission in Prokaryotic Cells
Replication of circular DNA and of plasmids
Division of cytoplasm to produce 2 daughter cells - have single copy of circular DNA and variable n7mber of plasmids
50
Plasma Membranes - Fluid-Mosaic Model
All cells and organelle membranes have same structure
Fluid-mosaic model - mixture and movement of phospholipids, proteins, glycoproteins and glycolipids
All these molecules arranged into phospholipid bilayer - create partially permeable membrane (cell surface membrane)
51
Phospholipid Bilayer
Align as bilayer - hydrophilic head attracted to water and hydrophobic tail repelled by water
Extra cellular and intracellular
52
Cholesterol presence in membranes
Present in some membranes
Restricts lateral movement of other molecules in membrane - membrane less fluid at high temps and prevents water and dissolved ions leaking out of cell
53
Glycoproteins and Glycolipids
Glycoproteins - protein with carb attached
Glycolipids - lipid with carb attached
54
Protein Channels
Form tubes that fill with water to enable water-soluble (polar) ions to diffuse
55
Carrier proteins
Bind to larger molecules like glucose and amino acids and change shape to transport them to other side of membrane
56
Molecules that can pass through plasma membrane
Lipid soluble substances
Very small molecules
(CO2, O2, H2O)
57
Molecules that can’t pass through plasma membrane
Water soluble (polar) substances (Sodium Ions)
Large molecules (Glucose)
58
5 types of transport across membranes
Simple Diffusion
Facilitated Diffusion
Osmosis
Active Transport
Co-transport
59
Simple Diffusion
Net movement of molecules from area of higher concentration to area of lower concentration, until equilibrium is reached
Doesn’t require ATP - uses kinetic energy
Lipid soluble and small to diffuse across membrane
60
Facilitated Diffusion
Passive process - proteins used to transport molecules
Ions and polar molecules which can’t simply diffuse are transported across membrane using protein channels and carrier proteins
61
Osmosis
Movement of water from area of higher water potential to area of lower water potential across partially permeable membrane
62
Water potential
Pressure created by molecules
Measured in kPa
63
Pure water water potential
0
64
Isotonic Solution
Water potential same in solution and cell in solution
65
Hypotonic
Water potential of solution more positive (closer to 0) than cell
66
Hypertonic
Water potential of solution more negative than cell
67
Active Transport
Movement of substance from low concentration to high concentration using metabolic energy and a carrier protein
68
Steps of Active Transport
1. Transport through carrier protein across cell membrane
2. Molecules binds to receptor complementary shape to protein
3. ATP binds to carrier protein from inside of cell and hydrolysed into ADP+Pi
4. Causes carrier protein to change shape and release molecule to other side
5. Phosphate ion released and protein returns to original shape
69
Co-transport of glucose and sodium ions in the ileum
To absorb glucose from lumen to gut there must be a higher concentration of glucose in lumen to epithelial cell (for facilitated diffusion)
BUT
Usually more glucose in epithelial cells so active transport and co-transport are required
70
Steps of co-transport of glucose and sodium ions in the ileum
1. Sodium ions actively transported out of epithelial cell into blood
2. This reduces sodium ions concentration in epithelial cell
3. Sodium ions can diffuse from lumen down concentration gradient into epithelial cell
4. Protein, the sodium ions diffuse through a co-transported protein - glucose or amino acids also attach and transported into epithelial cells against concentration gradient
5. Glucose moves by facilitated diffusion from epithelial cells to blood
71
Adaptations for rapid transport across membranes
Increased SA
Increased number of protein channels and carrier protein molecules in their membranes
72
Lymphocytes
Cells that are part of the immune system
Identify presence of pathogens and harmful foreign substances to then destroy or neutralise them
73
Identifying self and non-self cells
Each type of cell has specific molecules on surface that identify it. These molecules, usually proteins as 3D tertiary structure allows lots of unique and identifiable shapes to be made.
If a non-self cell is identified, a response is triggered to destroy it.
74
Different surface molecules enable lymphocytes to identify:
Pathogens (bacteria, fungi, HIV)
Cells from other organisms of same species (harmful for those with organ transplants)
Abnormal body cells (cancer cells)
Toxins - some pathogens release toxins into blood (cholera)
75
Antigen
Molecules that generate immune response by lymphocyte cells when detected in body
Usually protein
Located on surface of cells
76
Antigen Variability
Pathogens DNA can mutate frequently - mutation in gene coding for antigen = change antigen shape
Previous immunity to pathogens no longer effective - all memory cells have old antigen shape (flu virus, influenza)
77
Immune Response
If pathogen gets past chemical and physical barriers (skin and stomach acid) and enters the blood then white blood cells are the second line of defence
White blood cells have specific and non-specific responses
78
Specific response
Lymphocytes
79
Non-specific response
Phagocytes
80
Phagocyte
Macrophage (WBC) that does phagocytosis
Blood and in tissues
81
Steps of Phagocytosis
Non-specific response - same response to destroy anything
1. Many receptor binding points on surface. Attach to chemicals or antigens on pathogen via these receptors.
2. Phagocyte changes shape to move around and engulf the pathogen
3. Once engulfed, pathogen contained within phagosome vesicle
4. Lysosomes within phagocyte fuse with phagosome and release its contents
5. Lysozyme enzyme released into phagosome - hydrolyses pathogen
82
T Lymphocytes
All lymphocytes made in bone marrow, but T cells mature in thymus
Cell-mediated response involves T cells and body cells
83
Cell mediated response
Involves T cells and body cells
Once pathogen is destroyed, antigens are positioned on cell surface - Antigen Presenting Cell (APC)
Helper T cells have receptors on surface which attach to antigens on APC
Once attached this activates the helper T cells to divide by mitosis to replicate and make clones.
84
Cloned helper T cells differentiate into different cells:
Some remain as helper T cells and activate B lymphocytes
Some stimulate macrophages for more phagocytes
Some become memory cells for that shaped antigen
85
B lymphocytes
B cells made and mature in bone marrow
Humoral response involves B cells and antibodies
Antibodies are soluble and transport in bodily fluids
86
B cell Activation
1. B cell is triggered when it encounters its matching antigen
2. B cells engulfs antigens on APC and digests it
3. Display antigen fragments bound to its unique MHC molecules
4. Combination of antigen and MHC attracts help of mature matching T cell
5. Cytokinesis secreted by T cell help the B cell to multiply and mature into antibody, producing plasma cells
6. Released into blood, antibodies lock onto matching antigens. Antigen-antibody complex.
87
Memory B cells
Live for decades
Don’t make antibodies - instead divide by mitosis and make plasma cells rapidly if they collide with an antigen they previously encountered
Results in large numbers of antibodies being produced so fast that pathogen destroyed before any symptoms can occur.
88
Antibodies
Quarternary structure protein (4 polypeptide chains)
Variable region
Light chain
Heavy chain
Constant region
89
Antibodies - agglutination
Antigen-antibody complex
Antibodies are flexible and can bind to multiple antigens to clump them together - easier for phagocytes to locate and destroy the pathogens
90
Passive Immunity
Antibodies are introduced into the body
Pathogen doesn’t enter the body, so plasma cells and memory cells are not made
No long-term immunity
91
Active Immunity
Created by your own immune system following exposure to the pathogen or its antigen
Natural Active Immunity - following infection and the creation of antibodies and memory cells
Artificial Active Immunity - following introduction of weakened version of pathogen or antigens (vaccine)
92
Vaccines
Small amounts of weakened pathogen or antigens introduced to body (injection)
Exposure to antigen activates B cell to go through clonal expansion and differentiation (clonal selection)
B cells undergo mitosis to make a lot of cells, these differentiate into plasma cells or memory B cells
Plasma cells make antibodies
93
Herd Immunity
If enough of population are vaccinated, the pathogen cannot spread easily amongst the population
Provides protection for those who are not vaccinated
94
HIV structure
Core - genetic material (RNA) and the enzyme reverse transcriptase, which are needed for viral replication
Capsid - outer protein coat
Envelope - extra outer layer, made from membrane taken from host’s cell membrane
Protein attachments - on exterior of envelope to enable virus to attach to host’s helper T cell
95
Replication of HIV in helper T cells
- HIV transport per around in blood until attaches to a CD4 protein on helper T cells
- HIV protein capsule fuses with helper T cell membrane - enables RNA and enzymes from HIV to enter
- HIV enzyme reverse transcriptase copies viral RNA into a DNA copy and moves to helper T cell nucleus (why it’s called a retrovirus)
- Here mRNA is transcribed and helper T cell starts to create viral proteins to make new viral particles.
96
AIDS
HIV positive is when a person is infected with HIV.
AIDS is when the replicating viruses in the helper T cells interfere with their normal functioning of the immune system.
97
Monoclonal Antibodies
Single type of antibody that can be isolated and cloned
Antibodies are proteins which have binding sites complementary in shape to certain antigens.
Used in medical traetment, diagnosis and pregnancy tests
98
Direct Monoclonal Antibody Therapy
- Monoclonal antibodies designed with binding site complementary in shape to antigens on outside of cancer cells.
- Antibodies given to cancer patients and attach to cancer cells. While bound to cancer antigens, this prevents chemicals binding to cancer cells which enable uncontrolled cell division (tumours)
- don’t cause harm to other normal cells.
99
Indirect Monoclonal Antibody Therapy
- monoclonal antibodies with drugs attached to them
- cancer drugs delivered directly to cancer cells and kill them - reduces harmful side effects that traditionally come from chemotherapy and radiotherapy
- ‘bullet drugs’
100
Monoclonal Antibodies - Medical Diagnosis
MAs can be used for:
- pregnancy
- influenza
- hepatitis
- chlamydia
- prostate cancer
(E.g. COVID 16 antibody test)
Works via an ELISA test.
101
ELISA test
ELISA - Enzyme Linked Immunosorbent Assay
Uses two antibodies
- first mobile antibody, complementary to antigen being tested for, has coloured dye attached
- second antibody complementary in shape to antigens on outside is immobilised in the test
- third antibody is immobilised and is complementary in shape to first antibody
102
Steps of ELISA test
1. Add test sample from patient to base of beaker
2. Wash to remove any unbound test sample
3. Add antibody complementary in shape to antigen testing for in the test sample
4. Wash to remove any unbound antibody
5. Add second antibody complementary in shape to first antibody, and binds to first. Second antibody has enzyme attached to it. Rinse unbound antibodies off.
6. Substrate for enzyme (colourless) is added - produces coloured products in presence of the enzyme
7. Presence of colour indicates presence of antigen in test sample and intensity of colour indicates quantity present
103
Ethical Considerations of Monoclonal Antibodies
- requires mice to produce antibodies and tumour cells - whether use of animals is justified to enable the better treatment of cancers in humans and to detect disease
