C1 - Cells and Microscopy Flashcards
1
Q
What’s a multicellular organism made up of?
A
Hundreds - Billions of cells
Each type of cell has a specific internal structure which makes it efficient for its role.
2
Q
What is compartmentalisation?
A
When the internal structure of a cell is/can be divided up into areas specialised for specific functions.
3
Q
What is a leucocyte?
A
A white blood cell - they are eukaryotic cells, meaning they possess a distinct nucleus and membrane-bound organelles.
4
Q
How can the structure of organelles be studied?
A
By using an electron microscope.
5
Q
What is an eukaryotic cell?
A
A cell that has a true nucleus (contained by a nuclear envelope) which contains membrane-bound organelles in the cytosol such as the Golgi apparatus.
6
Q
How are eukaryotic cells membrane-bound?
A
All organelles within an animal cell are contained by the cell surface membrane.
7
Q
What is the nucleus of a cell and what does it contain?
A
The most important structure of a eukaryotic cell.
It’s a large, spherical organelle 10-20 um in diameter surrounded by a double membrane, the nuclear envelope.
It contains genetic, hereditary material DNA and controls the cell’s activities.
8
Q
What is the nuclear envelope and what does it do?
A
A (porous) membrane surrounding the nucleus.
It controls the entry and exit of materials to and from the nucleus.
There are typically 3000 pores which allow the passage of large molecules out of the nucleus e.g. messenger RNA (mRNA).
9
Q
Why does the nuclear envelope have pores?
A
To allow the passage of large molecules out of the nucleus.
10
Q
What is the liquid within the nucleus?
What does it contain?
A
Nucleoplasm - it contains the chromatin (DNA) and the nucleolus (a small spherical structure that produces ribosomal RNA (rRNA) and assembles the ribosomes)
11
Q
What is nucleoplasm?
A
The liquid in the nucleus which contains chromatin (DNA) and the nucleolus.
12
Q
What’s the nucleolus?
A
A small spherical structure that produces ribosomal RNA (rRNA) and assembles the ribosomes.
Its main function is to rewrite ribosomal RNA (rRNA) and combine it with proteins. This results in the formation of incomplete ribosomes.
13
Q
What is the function of the nucleus?
A
To control the activities of the cell via the production of mRNA
To contain the genetic material in the form of DNA coiled around proteins to form linear chromosomes
To manufacture rRNA and ribosomes
14
Q
What are cristae?
A
Folds in the inner membrane of mitochondria
They increase the surface area
15
Q
What are mitochondria?
A
Rod-shaped organelles (between 1-10um in length).
They are surrounded by the mitochondrial envelope - (the outer membrane controls materials entering and exiting the mitochondrion and the inner membrane is folded to form the cristae)
16
Q
What is the purpose of cristae?
A
To provide a larger surface area for enzymes involved in the synthesis of ATP to be attached to.
17
Q
What is the matrix?
A
The liquid inside the cristae (the matrix) which contains proteins (including enzymes for the breakdown of carbohydrates), lipids and small amounts of circular DNA.
The substance between cells or in which structures are embedded
18
Q
What’s the function of the mitochondria?
A
To carry out the later stages of aerobic respiration.
To produce ATP, an energy transfer molecule.
19
Q
What is the endoplasmic reticulum?
A
The ER is a series of flattened membrane-bound tubules that spread through the cytoplasm.
The membrane bound sacs are called cisternae.
It comes in two types: SER and RER
“A network of membranous tubules within the cytoplasm of a eukaryotic cell, continuous with the nuclear membrane. It usually has ribosomes attached and is involved in protein and lipid synthesis.”
20
Q
What are cisternae?
A
A fluid-containing sac or cavity in the body of an organism. / One of the saclike vesicles that comprise the endoplasmic reticulum.
The ER consists of a network of membrane lamellae and tubules called cisternae; the internal space of the ER is called the cisternal space or the lumen.
21
Q
What is smooth endoplasmic reticulum?
What’s its function?
A
SER is cisternae that are often tubular in appearance.
It’s function is to synthesis, store and transport lipids and carbohydrates.
22
Q
What is rough endoplasmic reticulum?
What’s its function?
A
RER is cisternae which has ribosomes attached to its outer surfaces.
It is continuous with the outer nuclear membrane.
It’s function is to provide a large surface area for protein and glycoprotein synthesis and to provide a pathway for transporting proteins and other materials through the cell.
It makes proteins for the membrane or for outside the cell transported by blood (meanwhile ordinary/free ribosomes make protein for the inside of the cell)
23
Q
Are ribosomes organelles?
A
Ribosomes are not organelles.
They are not membrane-enclosed, instead they are macromolecules made of both RNA and proteins.
If you ever have trouble remembering, just recall that there are ribosomes found in bacteria even though bacteria do not contain organelles.
24
Q
What are ribosomes?
A
They are NOT membrane bound organelles - they are cytoplasmic granules made from rRNA and protein.
They’re found free in the cytoplasm or with the rough ER.
25
What is the role of ribosomes?
To join amino acids in a specific order, the order of which is dictated by messenger RNA (mRNA) molecules.
The small ribosomal subunit reads the RNA and the large subunit joins amino acids together to form polypeptide chains.
26
How are proteins made?
Messenger RNA (mRNA)
Ribosomes are the site of protein synthesis.
They are found in the cytoplasm but DNA is found in the nucleus.
The genetic code needed to make a particular protein is carried from the DNA to the ribosomes by a molecule called mRNA.
Making:
mRNA from DNA is called transcription
Proteins from mRNA is called translation
27
What are Svedberg units of measure?
| How does it relate to ribosomes?
A measure of the sedimentation rate of particles e.g. Rate for the substance to reach the bottom of a tube in centrifuge. (Unit S)
Ribosomes in eukaryotic cells are 80S 20-30nm in diameter with a ratio of 1:1 (rRNA:proteins)
Each consists of a small 40S subunit and a large 60S subunit
28
What's the Golgi apparatus?
Similar to the smooth ER in appearance, it is made from a stack of membrane bound sacs (cisternae) and small, hollow, spherical vesicles.
(Typically 40-100 stacks (3-6 cisternae per pack)).
29
What takes place within the Golgi apparatus?
Proteins and lipids made in the ER are passed to the Golgi apparatus by the addition of non-protein portions
(e.g. Oligosaccharides or glycans to form a glycoprotein or by the addition of phosphates)
The Golgi apparatus labels the proteins to enable them to be accurately sorted and transported to their correct destinations.
After modification, the proteins and lipids are packed into vesicles which bud off from the ends of the Golgi apparatus for transport around the cell.
30
What happens to the proteins and lipids produced in the endoplasmic reticulum?
They're transported to the Golgi apparatus via vesicles which then receives the proteins and lipids.
It then sends them to where they're needed via more vesicles and go to the cell membrane where the proteins make a channel so large molecules can lass through and enter the blood.
31
What are the functions of the Golgi apparatus?
To assemble polypeptides into proteins
To pack proteins and carbohydrates into vesicles for secretion by exocytosis
32
What's exocytosis?
Exocytosis describes the process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.
(E.g. Secretion)
33
What's endocytosis?
Endocytosis is the process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane, and bringing it into the cell.
(E.g. Uptake)
34
What are vesicles?
| What do they do?
Small, fluid containing, membrane-bound organelles.
They're used in processes like secretion (exocytosis), uptake (endocytosis) and transport of minerals in the cytoplasm.
They're also involved in transport within the cell, cell metabolism and enzyme storage.
35
What's phagocytosis?
A type of endocytosis
| The ingestion of bacteria or other material by phagocytes and amoeboid protozoans.
36
What are lysosomes?
Spherical membrane-bound vesicles (sacs) that are produced by the Golgi apparatus.
They contain up to 50 different types of enzymes (usually proteases and lipases)
They're typically 1um diameter and pH of 5
37
What is the function of lysosomes?
To digest unwanted materials in the cytoplasm.
They have an important role in phagocytosis where they fuse with phagocytic vesicles so the enzymes can digest engulfed pathogens.
38
What's a centriole?
Each of a pair of minute cylindrical organelles near the nucleus in animal cells, involved in the development of spindle fibres in cell division.
A centriole is a small set of microtubules arranged in a specific way.
There are nine groups of microtubules.
When two centrioles are found next to each other, they are usually at right angles.
The centrioles are found in pairs and move towards the poles (opposite ends) of the nucleus when it is time for cell division.
39
What's the plasma membrane?
A microscopic membrane of lipids and proteins which forms the external boundary of the cytoplasm of a cell or encloses a vacuole, and regulates the passage of molecules in and out of the cytoplasm.
The plasma membrane is the boundary between the cell and its environment.
It regulates what enters and exits the cell. Cells must maintain an appropriate amount of molecules to function inside them.
40
What are peroxisomes?
A small organelle present in the cytoplasm of many cells, which contains the reducing enzyme catalase and usually some oxidases.
41
What's the cytoskeleton?
A microscopic network of protein filaments and tubules in the cytoplasm of many living cells, giving them shape and coherence.
The cytoskeleton is a structure that helps cells maintain their shape and internal organization, and it also provides mechanical support that enables cells to carry out essential functions like division and movement.
There is no single cytoskeletal component. Rather, several different components work together to form the cytoskeleton.
42
What are micro villi?
Folded plasma membranes
43
What's the cytosol?
The aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended.
Cytoplasm is the cytosol and the organelles.
44
What are microtubules?
Hollow filaments of protein tubules which give structural support and are part of the cytoskeleton and form organelles e.g. Centrioles and cilia.
45
What's the chromatin?
Granular material in the nucleoplasm.
| During cell division it condenses into more tightly coiled threads called chromosomes.
46
What are erythrocytes?
Red blood cells (the most common type of cell)
They develop in the bone marrow and circulate within the blood for 100-120 days.
In humans, mature red blood cells are flexible and oval biconcave discs.
47
What is the function of erythrocytes?
To deliver oxygen from the lungs to the body.
They contain haemoglobin, an iron containing protein that can bind reversibly with oxygen to form oxyhemoglobin.
48
Erythrocytes (red blood cells) lack a cell nucleus and most organelles.
What does this enable them to do?
Have a large surface area to volume ratio
Become biconcave, enabling them to be flexible and squeeze through capillaries
49
How are erythrocytes produced?
They're produced in bone marrow from erythropoietic stem cells in a process called erythropoiesis.
Erythropoiesis is stimulated by the hormone 'erythropoietin' (EPO) which is produced by the kidney
50
What's erythropoiesis?
The process of the production of erythrocytes in bone marrow from erythropoietic stem cells.
51
What are reticulocytes?
Immature red blood cells.
They have no nucleus and can be identified in a blood smear when stained with methylene blue.
52
What are thrombocytes?
Platelets
They are biconvex discs of cytoplasm fragments / cell fragments surrounded by a cell surface membrane.
They're produced in bone marrow (by megakaryocytes) and have no nucleus
On a stained blood smear, platelets appear as dark purple spots.
53
What is the function of thrombocytes?
To assist the clotting and clot formation of the blood to prevent bleeding.
A blood clot is also known as a thrombus.
This is done by the thrombocytes binding to the injured tissue (adhesion), changing shape, connecting together and forming a bridge.
54
What is thrombogenesis?
(Coagulation) is when the blood changes into a gel.
55
What are leucocytes?
White blood cells - important for the immune system.
There are 5 types of leucocytes and they're larger than erythrocytes (but less abundant)
56
What are the two categories of leucocytes?
Granulocytes - contain granules (usually lysosomes) in their cytoplasm which all stain differently.
E.g. Neutrophils
Agranulocytes - have an absence of granules in their cytoplasm.
E.g. Lymphocytes, monocytes and macrophages
57
What are neutrophils?
Neutrophilic (readily stained by natural dyes) white blood cells.
On a blood smear, a multi lobed nucleus can be seen.
They're unable to renew their lysosomes therefore die after breaking down a few pathogens.
58
What is the function of neutrophils?
They help the body defend against fungal or bacterial infections.
They engulf and break down bacteria in the process of phagocytosis.
They have the ability to leave capillaries by squeezing through the fenestrations (pores in endothelial cells) in the capillary wall, made possible due to having a lobed nucleus which makes them flexible.
59
What are lymphocytes?
A small form of leucocyte (white blood cell).
They have a large, deeply stained nucleus surrounded by a small amount of cytoplasm.
60
What are the two groups of lymphocytes?
B-Lymphocytes: produce immunoglobulin a.k.a antibodies
T-Lymphocytes: (have several types)
- 'helper T cells' produce cytokines and help coordinate the immune response
- 'cytotoxic T cells' bind to antigens on virus infected cells or tumour cells and destroy them
- Natural killer cells
(Both look the same on blood smears)
61
What are monocytes?
The largest type of leucocyte (white blood cells)
They carry out phagocytosis, similar to neutrophils, but they live much longer.
Eventually, they leave the blood stream and differentiate into tissue macrophages (which remove dead cell debris and attack microorganisms) (macrophages are found in the lungs, liver and lymph nodes.
They have a kidney bean shaped nucleus and are typically agranulated so the cytoplasm appears clear.
62
How is magnification calculated?
Total magnification = eye piece magnification * objective magnification
Magnification = size of image / size of object
63
How do you calculate the size of one eyepiece graticule unit?
Distance of one eyepiece graticule unit = stage micrometer / eyepiece graticule units
64
What's the structure of a palisade mesophyll cell?
Upper epidermis
Palisade mesophyll cells
Spongey mesophyll cells
Lower epidermis
The palisade mesophyll cells are the main site for photosynthesis and are also eukaryotic cells with organelles the same as animal cells as well as additional organelles found in plants:
Chloroplasts
Vacuole
Cell wall
65
What are chloroplasts?
An organelle in green plant cells which contains chlorophyll and in which photosynthesis takes place.
They're usually disc shaped, 2-10um long and 1um in diameter.
66
What are the three membrane systems of chloroplasts?
The outer chloroplast membrane - this outer layer of the envelope allows small molecules and ions to easily diffuse across but not large proteins
The inner chloroplast membrane - is in contact with the fluid filled centre of the chloroplast (the stroma) and controls the passage of materials in and out of the stroma.
It's also the site of fatty acids, lipids and carotenoids synthesis.
The inner membrane is continuous with the thylakoid system.
The thylakoid system - are suspended in the stroma. They're made from a collection of membrane bound sacs called thylakoids. Chlorophyll molecules and other photosynthetic pigments are found embedded in the thylakoid membranes.
67
What's the stroma?
The fluid filled centre of the chloroplast where the second stage of the process of photosynthesis occurs (light independent stage).
It contains DNA, chloroplast ribosomes (70s), starch granules and many proteins.
68
What are vacuoles?
Large vesicles that contain mainly water.
Its contents is separated from the cytoplasm by a membrane called the tonoplast.
Salts, sugars and organic acids are dissolved in the water.
Mature plant cells usually have a large central permanent vacuole which plays an important role in cell turgidity and overall plant support
69
What is the cell wall made of?
What's its importance?
The polysaccharide cellulose.
Within the wall, cellulose microfibrils are held together by hydrogen bonds. The microfibrils form cross links which gives the cell wall strength and prevents it from bursting when water enters by osmosis.
It also allows water to pass along the microfibrils to aid the passage of water through the plant
70
What is a prokaryotic cell?
A cell that does not have a true nucleus, nuclear envelope or any true membrane-bound organelles, such as bacteria like Escherichia Coli and blue-green algae.
They are usually smaller than eukaryotic cells with smaller volumes however they have features which are unique to them.
71
Where is the genetic information found in prokaryotic cells?
In the circular DNA which contains the genetic information for replication and protein synthesis
72
What are plasmids?
Very small circular pieces of DNA, physically separate from the main DNA within the cell.
Plasmids can replicate independently from the main DNA and carry genes that increase the survival of the bacteria e.g. The genes to produce enzymes that break down antibiotics
73
What's the mesosome?
It has been proposed as the possible site for respiration but more recent studies suggest that such structures might be artefacts produced during the preparation of specimens for electron microscopy.
The mesosome is formed by invagination of the cell surface membrane.
74
What are pili?
Hair-like structures made of protein which extend through the cell wall
They help bacteria to stick (adhere) to each other or to other surfaces however they are not found in all bacteria
75
What is a flagellum?
Like a tail, used for locomotion.
Some prokaryotic cells have a flagellum which is used for movement.
Bacterial flagellum rotate due to the presence of a rotating bearing at the base of the flagellum (smallest known motor)
E.g. The Helicobacter pylori, which causes stomach ulcers, uses multiple flagella to propel itself.
76
Advantages and disadvantages of light microscopes:
```
Adv:
It enables the observation of a wide range of specimens me living organisms e.g. Daphnia and euglena.
Easy to use
Quite cheap
Easily transported
```
Disadv:
Due to limited resolution, most intercellular structures cannot be seen
77
Some animal cells are 50um in diameter.
If a cell is observed under a microscope that can magnify the specimen by 1500, calculate the diameter of the cell in the image in mm
Magnification = image size / object size
50 * 1500 = 75,000
75,000 / 1000 = 75 (um to mm)
75 mm
77
At a magnification of 14,000x a structure appears 8mm long
Calculate the actual length of the specimen in um:
Magnification = image size / object size
8 mm = 8000um
8,000 / 14,000 = 0.57
= 0.6 um
77
What's EM?
Electron microscopy is a more complex type of microscope that creates an image using a beam of electrons as the form of radiation.
Using a beam of electrons which have a shorter wavelength results in a much greater resolving power (0.1nm)
78
Advantages and disadvantages of electron microscopy:
Adv:
- Greater resolving power (0.1nm)
- This is a significant advantage over the light microscope as higher magnifications can be achieved, enabling smaller objects and finer details to be seen.
Disadv:
- They are large and expensive
- They require a trained person to use them as well as a specially designed room to be used in the electrons are negatively charged so the beam of electrons can be focused using electromagnets which make up the condenser
- Specimens must be placed into a near vacuum as air molecules absorb the electrons. This means the specimens must be dehydrated and dead.
- A complex staining process is also needed to prepare specimens.
As the human eye is not able to detect electrons electrons a focus on to a fluorescent screen which emits visible light where the electrons hit.
The visible image on the screen is called a photomicrograph.
Black and white
79
What's a TEM?
Transmission electron microscope
Specimens observed must be thinner than those observed by light microscopes as electrons cannot penetrate materials as well as light.
Heavy metals stain the specimens as their atoms have large, positively charged nuclei that scatter the electrons.
Those scattered don't hit the fluorescent screen so leave a dark area in the image.
2D black and white
80
What's an SEM?
Scanning electron microscope
Electrons don't pass though the actual specimen.
The electron beam is passed backwards and forwards over the specimen surface in a regular pattern.
The pattern of scattered electrons reflects the contours of the specimen and this information is used to produce a 3D image with computer analysis.
81
What's CLSM?
Confocal laser scanning microscopy
Obtains high resolution 3D reconstructions. It's main advantage is it's ability to produce focused images of thick specimens, known as optical sectioning.
(Point light source, point fluorescent light, scan object, combine optical sections.)
82
What is the sequence of protein synthesis?
1) The gene for the production of the protein is located in the nucleus
2) The genetic info for the production of the specific protein is copied into mRNA by transcription
3) The mRNA leaves the nucleoplasm via the nuclear pore and enters the cytoplasm
4) The mRNA attaches to a ribosome (from the RER or free)
5) The ribosome reads the RNA in the mRNA and translates them into a polypeptide chain
6) The assembled protein in the RER is pinched off in a vesicle and is transported to the Golgi apparatus through the cis face
7) The G.A. packages the protein
8) The Golgi vesicle moves to the cell surface membrane by the cytoskeleton from the trans face where it is secreted out by exocytosis
83
What are the three main types of cytoskeleton filaments?
What's their purpose?
Micro filaments - made from actin and are the thinnest filaments
Intermediate filaments - more stable than micro filaments. They are made of proteins such as keratin
Micro tubules - made from a specialised protein called tubulin arranged in hollow cylinders.
They maintain the cells structure and shape and are important for intra cellular transport and mitosis.
Molecules called motor proteins provide the driving force to move organelles and chemical substances along these filaments.
84
Where are cell membranes found?
What do cell membranes do within eukaryotic cells?
They exist around cells and around eukaryotic cell organelles.
```
They:
Control the entry/exit of molecules in organelles
Isolate organelles
Provide a transport system
Concentrate and isolate enzymes
Maintain specific conditions
Provide surfaces for chemical reactions
```
85
What are the components of cell membranes?
Phospholipids
Cholesterol
Proteins
86
What are lipids?
Substances (fats) that are insoluble in water, cytosol and other aqueous solutions but are soluble in organic solvents e.g. Ethanol.
They're present in all living cells as they're an essential part of the cytoplasm.
Most are found in the adipose tissue (used for storing fats) of animals and in oily seeds in plants e.g. Peanuts.
Fats and oils are the same however fats are solid at 20° meanwhile oils are liquid.
87
What are the roles of lipids?
Heat insulation - in mammals, adipose tissue beneath the skin helps reduce heat loss
Energy - twice as much as carbohydrates
Protection - adipose tissue around delicate organs e.g. the kidneys acts as a cushion against impact
88
What's a fatty acid?
A carboxylic acid (COOH) with a long unbranched hydrocarbon tail (the length of which differs)
Most fatty acids which naturally occur have an even number of carbon atoms in the hydrocarbon tail, from 4-28.
They can be saturated (all single bonds) or unsaturated (double bonds).
89
What is a triglyceride?
An ester formed from glycerol and 3 fatty acids by a condensation reaction.
They are completely hydrophobic and aren't found in cell membranes.
A condensation reaction removes water from between the glycerol molecules (CH2OH) and fatty acids (COOH /\/\/\) to form ester bonds.
```
O
||
CH2O - C /\/\/\/\/\/\/\
O
||
CH2O - C /\/\/\/\/\/\/\
O
||
CH2O - C /\/\/\/\/\/\/\
```
& H2O
90
What are properties of saturated fatty acids?
Have even numbers of carbon atoms e.g. Butter C3H7COOH
They're all straight compounds with NO double bonds
Solid at room temp
Do not react with bromine
91
What are properties of unsaturated fatty acids?
Has 1+ double bond
Low melting points
Turn bromine water colourless
Oleic acid is the most common (in olive oil)
A double bond in the chain causes a kink in he hydrocarbon chain
```
H
|
C=O
/
\__ __/
\__ __/
\__/
```
92
What are phospholipids?
The main component of cell membranes.
Each molecule has a hydrophilic phosphate head and a hydrophobic hydrocarbon tail.
They're made when one of the fatty acid groups in a triglyceride is replaced with a phosphate group.
93
What is a phosphate bilayer?
Spheres, micelles or sheets formed due to the hydrophilic and phobic parts of the phospholipid molecule.
They allow lipid-soluble molecules to cross the membrane
They prevent water-soluble molecules crossing the membrane
Allows the membrane to be flexible
Allows the membrane to be stable
94
What's cholesterol?
A lipid like substance (steroid) found throughout the cell surface and membranes.
Most of the molecule is hydrophobic so is attracted to the hydrophobic hydrocarbon tail in the centre of the membrane.
However one end is hydrophilic and attracted to the phosphate heads of the phospholipids.
95
What's the significance of cholesterol?
Provides strength to the cell membrane which is important in the absence of the cell wall and is important in regulating the fluidity of the membrane.
It prevents water and water-soluble ions leaking out of the cell and reduces lateral movement of the p.lipids within a mono layer.
96
Where are proteins found?
Floating within p.lipid bilayers as:
- Integral/intrinsic proteins within the bilayer
- Peripheral/extrinsic proteins found at the edges of the bilayer
Some extrinsic proteins are modified and have a carbohydrate portion added to them to form a glycoprotein. The carbohydrate molecules on the glycoproteins and glycolipids form a region called the glycocalyx. This has a role in adhesion of the cell.
97
What's the glycocalyx?
Some extrinsic proteins are modified and have a carbohydrate portion added to them to form a glycoprotein.
The carbohydrate molecules on the glycoproteins and glycolipids form a region called the glycocalyx.
This has a role in adhesion of the cell.
98
What are functions of membrane proteins?
Structural support
Carry molecules
Form ion channels for active transport
Help adherence of cells
Act as receptors for hormones and neurotransmitters
Act as antigens allowing cells to recognise one another
99
What's the fluid mosaic model?
A model showing where all of the components of the cell membrane are arranged.
It is described as:
- fluid as the individual phospholipid molecules can move laterally within a monolayer or flip between monolayers.
- mosaic as the proteins floating in the phospholipid bilayer vary in shape, size and structure, making a pattern?
100
What are the components of the fluid mosaic model?
| cross section of a cell membrane
Protein molecule spanning the phospholipid layer (and the pore in the centre) (intrinsic and extrinsic)
Hydrophilic heads of phospholipid molecules
Hydrophobic tails of phospholipid molecules
Cholesterol - adds strength
Glycolipid - acts as a recognition site e.g. for cholera toxins
Glycoprotein - branching carbohydrate portion of a protein acting as a recognition site for chemicals e.g. hormones
101
Which part of the cell surface membrane enables the passage of:
i) a molecule that is soluble in lipids
ii) a mineral ion
i) phospholipid
| ii) intrinsic layer
102
Explain what would happen to plasma membranes that had:
i) too much cholesterol
ii) too little cholesterol
i) The membrane would be too fluid and there would be a loss of control entering and exiting the cell
ii) The membrane would not be fluid enough therefore movement of the cell and substances within it would be restricted
103
What's a passive process?
One which doesn't require additional energy input e.g. simple diffusion.
104
What is simple diffusion?
The net movement of molecules from an area of high to low concentration down the concentration gradient. (passive)
Molecules [gas] collide with each other, resulting in movement and kinetic energy.
They spread out and become equally spaced out until they still have kinetic energy however there is no longer a concentration gradient so no more diffusion occurs.
There is no diffusion but the actual position of the molecules has changed, known as a dynamic equilibrium. (no net movement)
105
What affects the rate of diffusion?
```
Concentration gradient
Surface area
Diffusion distance
Size of the molecule
Cell membrane composition
```
106
What is facilitated diffusion?
A form of passive diffusion using channel proteins or carrier proteins.
Molecules that are water-soluble are not able to cross the cell membrane via simple diffusion (due to the phospholipid bilayer) so require specialised proteins to carry the molecules across the membrane.
107
What are channel proteins?
Specialised proteins used in facilitated diffusion.
They form selective 'pores'/aqueous 'tunnels' through the hydrophobic lipid bilayer, enabling ions to pass through.
Some channels are 'gated' meaning they can be opened or closed depending on the presence of a potential difference across the membrane or the presence of another molecule (the ligand)
108
What are carrier proteins?
Specialised proteins with a specific shape used in facilitated diffusion.
When the molecule binds to the protein it undergoes a conformational change (allostery) and passes the molecule to the other side of the membrane.
e.g. with the uptake of glucose and amino acids in the small intestine.
109
Why can't glucose molecules simply diffuse through the phospholipid bilayer?
They are water-soluble molecules and cannot diffuse through the hydrophobic centre of the bilayer easily.
110
What is an active process?
One which requires an additional input of energy.
Some molecules being transported across the membrane must be transported against the concentration gradient.
For this to occur, energy has to be added as the kinetic energy of molecules is insufficient.
This extra energy is supplied by the hydrolysis of ATP produced during cellular respiration.
111
What's active transport?
How does it work?
An active process enabling molecules to be transported across a membrane by the use of energy and specialised carrier proteins.
The carrier proteins embedded in the membrane span the whole membrane. Each is specific for a few molecules.
The molecule binds to a complementary binding site on the carrier protein.
ATP also binds to a separate binding site on the carrier molecule. The energy released from the hydrolysis of ATP is used to change the structure of the carrier protein which moves the molecule across the membrane.
The carrier protein has undergone a conformational change. Once the molecule is released, the carrier protein returns to its original shape.
e.g. uptake of iodine by blood or minerals by plants
112
What is bulk transport?
Mass movement of substances from one side of the cell membrane to the other in large quantities, not possible with active transport, by endocytosis and exocytosis.
113
What is endocytosis?
Bulk movement of material into the cell
114
What is exocytosis?
Bulk movement of material out of the cell
115
What are the 2 main types of endocytosis?
Pinocytosis - cells engulf liquid material
Phagocytosis - cells engulf solid material
116
What occurs during endocytosis?
Large quantities of materials are taken into the cell
The cell surface membrane folds around the materials outside the cell.
The ingested material is trapped in a membrane-bound vesicle or vacuole.
117
What occurs during exocytosis?
Large quantities of materials are removed from the cell.
It releases hormones from the cells that produce them (e.g. gastrin from G-cells of the stomach and duodenum, insulin from beta-cells of the pancreas)
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What's the radiation source of the different types of microscope?
Light microscope - light bulb focussed by lenses
Scanning electron microscope - high voltage tungsten filament (electron source) focussed by electromagnets
Transmission E.M. - high voltage tungsten filament (electron source) focussed by electromagnets
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What's the image produced from the different types of microscope?
Light microscope - 2D in colour
Scanning electron microscope - 3D in black and white
Transmission E.M. - 2D in colour
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What is 'sectioning'?
When biological specimens are cut into sections.
| They can be cut into longitudinal, transverse and oblique sections.
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What are the stages in preparing a temporary and permanent slide?
Temporary: sectioning, fixation, staining and mounting. (used for light microscopy, its quite quick and simple)
Permanent: fixation, dehydration, clearing, embedding, sectioning, staining and mounting.
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What is differential staining?
A method used on various plant tissues.
A differential stain makes some structures appear darker or a different colour to other structures.
E.g. in vascular tissue in plants, toluidine will stain lignified cell walls blue and cellulose cell walls purple, allowing xylem vessels to be distinguishable.
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What occurs in the differential staining of blood cells?
What stains are used?
There are 2 main types of cell: erythrocytes and leucocytes.
Erythrocytes can be clearly seen under a microscope but stains must be used to differentiate the types of leucocyte.
Romanowsky stains are used:
Leishman's stain - the blood is dried then fixed with methanol before being diluted with water and washed until pale pink.
Wright's stain - used for differential white blood cell counts
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How is a blood smear prepared?
1) A small drop of blood is placed at the end of a sterile, clean, dry microscope slide
2) A spreader is held at 30' and is pushed along the slide to spread the blood back over the slide, forming a smear
3) The microscope slide is labelled
4) The slide is allowed to dry in the air to enable the cells to stick to the slide.
5) A fixative is used to preserve the cells.
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Suggest why latex-free gloves are worn when preparing blood smears
To prevent contamination of the blood sample, protect the pathologist from any pathogens present and latex-free reduces allergies and skin reactions.
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Why must the slide be grease free?
To allow cells to adhere to the microscope slide
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What is meant by cryosectioning and when may it be used?
It means freezing the specimen before sectioning the tissue/specimen which is used in oncology (studying cancerous cells)
However freezing may distort the cell/damage the cell membrane
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What is the name of the specialised slide/counting chamber used to count cells?
A haemocytometer
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What rule is used when using a haemocytometer?
The North-West rule where cells lying on the north and west boundaries are counted and those on the south and east are ignored
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What is flow cytometry?
An electronic counting apparatus using a laser-beam passing over a stream of blood to count cells.
This allows analysis of the physical and chemical characteristics of the blood while counting thousands of particles per second.
It uses a: flow cell (liquid stream carrying cells single file), measuring system, detector, amplification system and computer.
Antibodies can be tagged to different fluorochromes which recognise and target specific antigens inside or on the surface of cells.
Lamps or lasers with various wavelengths excite the fluorochromes which causes the tagged cells to fluoresce so it can be counted.
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What is the purpose of vesicles?
They transport polypeptides to the Golgi body from the RER or transport substances out of the cell.
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Where do light dependent reactions occur within a plant cell chloroplast?
The granum (stacked thylakoids)
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Where do light independent reactions occur within a plant cell chloroplast?
The stroma (the fluid filled centre of the chloroplast)
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Is ATP required for simple diffusion, facilitated diffusion and active transport?
Simple - no
Facilitated - no
Active - yes
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Pathogenic proteins can be detected via diagnostic methods.
| Outline the role of antibodies in the detection of these proteins [in food samples]:
Use flow cytometry
The bacteria are tagged by antibodies labelled with fluorescent markers.
- The antibodies are immobilised (have a fixed location) and bind to antigens of the protein such as p60.
These antibodies would be linked to enzymes which produce colour reactions, identifying the presence of the proteins.
