Flashcards in 3. Cells And Movement Deck (98):
What are microscopes?
Instruments which magnify an image of an object.
What is the basic unit of life?
What is the material placed under a microscope referred to as?
What is the appearance of the object under a microscope called?
What is the equation relating magnification, image size and object size?
Object (actual) size =image size/magnification
What is the resolution of a microscope?
The minimum distance apart that two objects can be in order for them to appear as separate items.
What does resolving power depend on?
The wavelength or form of radiation used.
What is the resolution of a light microscope?
0.2 micrometers (ym)
What happens after the limit of resolution?
Increasing the magnification no longer leads to increased resolution - the object will just be more blurred.
What is cell fractionation?
The process where cells are broken up and the different organelles they contain are separated out.
What kind of solution is the tissue placed in before cell fractionation?
Cold - to reduce enzyme activity that might break down organelles
Isotonic - to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.
Buffered - to maintain the pH
What are the two stages in cell fractionation?
Homogenation and ultracentrifution
What happens in homogenation?
The cells are broken up by a homogeniser. This releases the organelles from he cells. The resultant fluid (homogenate) is filtered to remove any complete or large pieces of debris.
What happens in ultracentrifugation?
The tube of filtrate is placed in the ultra centrifuge and spun at a low speed.
Heaviest organelles, the nuclei, are forced to the bottom where they form a thin sediment.
Fluid at the top of the tube (supernatant) is removed leaving the sediment.
The supernatant is put in another tube and spun in the ultracentrifuge faster.
The whole process is repeated.
Which force do the organelles in an ultracentrifuge experience?
Order of organelles separated out (heaviest first) in an ultracentrifuge...
Nuclei - 1000 gravitational force - duration 10 mins
Mitochondria - 3500 "" - duration 10 mins
Lysosomes - 16500 "" - duration 20 mins
Ribosomes - 100000 "" - duration 60 mins
Why do light microscope have poor resolutions?
Long wavelength of light
What are the two main advantages of the electron microscope?
The electron beam has a very short wavelength and so the microscope has a high resolving power.
As electrons are negatively charged the beam can be focused using electromagnets.
Why in an electron microscope should there be a near vacuum?
Because electrons are absorbed by molecules in the air
What are the two types of electron microscope?
The transmission electron microscope (TEM)
The scanning electron microscope (SEM)
What is the resolution of a SEM?
20nm (as electron beam has shorter wavelength)
What is the resolution of a TEM?
0.1 nm (shorter wavelength)
What is the depth of focus on a SEM?
What is the depth of focus on a TEM?
What is the depth of focus on a light microscope?
How hard is specimen preparation for a light microscope?
How hard is specimen preparation for a SEM?
Easy – the object must be thin but not as thin as in the TEM
How hard is specimen preparation for a TEM?
Skilled (object must be very thin)
Advantage of light microscope
We can view live specimens ( and in colour)
Disadvantage of light microscope?
Poor resolution - light has a long wavelength
What is the main advantage of a SEM?
Can view 3D structure
What is the main advantage of a TEM?
Very high resolution to view the smallest organelles.
What are the limitations of SEM and TEMs?
Black and white images
The whole system must be in a vacuum
Complex staining process required
Specimens must be thin (particularly for TEM)
Artefacts can be seen on photomicrograph (not part of the original specimen).
The internal structure which suits the function of the cell.
What is the role of the nucleus? (Short)
The nucleus contains the organisms hereditary material and controls the cells activities
List and describe the different parts of the nucleus
The nuclear envelope : a double membrane surrounding the nucleus. It's outer membrane is continuous with the endoplasmic reticulum and often has ribosomes on its surface. It controls the entry and exit of materials in and out of the nucleus and contains reactions
Nuclear pores: allow large molecules such as messenger DNA out of the nucleus.
Nucleoplasm: granular jelly-like material making up bulk of nucleus.
Chromatin: loosely coiled DNA
Nucleolus: manufactures ribosomes
What are the three functions of the nucleus?
Control protein synthesis
Retain the genetic material of the cell
What is the function of mitochondria?
Site of aerobic respiration
Describe the mitochondrion
They have a double membrane
Inner: forms extensions known as cristae which provide a large surface area for the attachment of enzymes involved in respiration.
Outer: controls entry and exit of materials
Large numbers of mitochondria where...
High metabolic activity e.g muscle cells - need higher levels of ATP and so more mitochondria with more cristae
What does the rough endoplasmic reticulum do?
Makes proteins - large surface area
(Has ribosomes on surface)
What does smooth endoplasmic reticulum do?
Makes,stores and transports lipids
Makes stores and transports carbohydrates
Lacks ribosomes on its surface
What kind of cells have extensive ERs?
Ones that need to manufacture and store large quantities of carbohydrates, proteins and lipids. E.g liver cells and epithelial cells in the lining of the intestines (epithelial is secretory)
What are the functions of the Golgi apparatus?
Add carbohydrate to proteins to form glycoproteins
Produce secretory enzymes (such as those in the pancreas)
Secrete carbohydrates such as those used in making cell walls in plants.
Transport modify and store lipids
In which cells is the Golgi apparatus especially well developed?
Secretory cells, like the epithelial cells which line the intestines
What are lysosomes?
Lysosomes are formed when the vesicles produced by the Golgi apparatus contain enzymes such as proteases and lipases.
How many enzymes can be contained in a single lysosome?
50 different enzymes
Where do lysosomes release their enzymes?
Either to the outside or into a phagocytic vesicle within the cell.
What are the functions of a lysosome?
Break down material ingested by phagocytic cells
Release enzymes to the outside of the cell in order to destroy material around the cell.
Digest worn out organelles so that the useful chemicals they are made of can be re-used.
Completely breakdown cells after they have died (autolysis)
In which cells are lysosomes particularly abundant?
Secretory cells such as epithelial cells and in phagocytic cells.
What do ribosomes do?
What are the two types of ribosome?
80s and 70s
Which type of cell do you find 80s ribosomes?
In eukaryotic cells
In which type of cell do you find prokaryotic cells?
70s (smaller than 80s)
What size and how many sub units do ribosomes have?
Two - one large and one small
What do ribosomes contain?
Ribosomal RNA and protein
Which organelle can account for up to 25 per cent of the dry mass of the cell?
Which synthesis are ribosomes important to?
What are microvilli? (Short definition)
Microvilli are finger-like projections of the epithelial cell that increase it's surface area to allow for more efficient absorption.
What elements do lipids contain?
Carbon, hydrogen and oxygen
Are lipids soluble or insoluble in water?
What solvents are lipids soluble in?
Organic solvents like alcohols and acetone.
What are the three main groups of lipids?
Triglycerides (fats and oils), phospholipids and waxes
What is the main role of lipids?
They form the plasma membrane (phospholipids contribute to the flexibility and the transfer of lipid soluble substances across them).
What are the roles of lipids? (5)
Lipids act as an energy source. How much energy do they provide?
When oxidised lipids provide more than twice the energy as the same mass of carbohydrate.
Why can lipids contribute to waterproofing?
They are insoluble in water. Plants have waxy cuticles to conserve water and mammals produce oily secretion from the sebaceous glands in the skin.
How do lipids function in insulation?
Fats are slow conductors of heat and help to retain body heat.
How does fat protect?
Delicate organs like such as the kidneys are surrounded by fat for protection.
What state is fat in at 10-20 degrees?
What state is oil in at 10-20 degrees?
What are triglycerides made up of?
Three fatty acids and a glycerol
Each fatty acid forms a bond with glycerol in what reaction?
What is the process called where you split up a triglyceride?
Where do the differences in properties of different fats and oils come from?
The different fatty acids. (The glycerol molecule is the same in all triglycerides)
How many fatty acids are there and chat group do they all have in common?
There are over 70 different fatty acids and they all have a carboxyl group -COOH with a hydrocarbon chain attached
When the hydrocarbon chain of a fatty acid has no carbon to carbon double bonds what is it described as?
If there is a single double bond on a hydrocarbon chain on a fatty acid what is it called?
If there is more than one double bond on a hydrocarbon chain of a fatty acid what is it called?
How is a phospholipid different from a lipid (triglyceride)?
One of the fatty acid molecules is replaced by a phosphate molecule.
Are fatty acid molecules hydrophobic or hydrophilic?
Are phosphate molecules hydrophobic or hydrophilic?
How many parts is a phospholipid made out of?
Describe the parts of a phospholipid.
A hydrophobic head - interacts with water but not fat
A hydrophilic head - mixes with fat readily but orientates itself away from water
Molecules which have two ends are...
Polar (when placed in water they position themselves in accordance with hydrophobic/hydrophilic parts.)
What is the test for lipids?
Take a completely dry and grease free test tube
To 2cm of the sample being tested add 5cm of ethanol
Shake the test tube thoroughly to dissolve any lipid in the sample
Add 5cm of water and shake gently
A cloudy-white colour indicates the presence of a lipid
As a control repeat the procedure using water instead of the sample - the final solution should remain clear.
In the test for lipids why does a cloudy white colour appear?
The lipid in the sample is finely dispersed in the water to form an emulsion. Light passing through the emulsion is refracted as it passes from oil droplets to water droplets.
What is the basic structure which makes up membranes?
The plasma membrane
What do cell-surface membranes form a boundary between?
Cell cytoplasm and the environment
What is the function of the plasma membrane?
It controls the movement of substances in and out of the cell.
What type of sheet do phospholipids form in the cell-surface membrane?
A bilayer sheet
Why are phospholipids important components of the cell-surface membrane?
One layer of phospholipids has it's hydrophilic head pointing inwards (interacting with water in the cell cytoplasm) the other has it's head pointing out wards (interacting with the water which surrounds all cells).
The hydrophobic tails of both phospholipid layers point into the centre of the membrane.
The functions of the phospholipids in the membrane are to...
Allow lipid-soluble substances to enter and leave the cell
Prevent water-soluble substances entering and leaving the cell
Make the membrane flexible
Aside from phospholipids what else is in the cell-surface membrane?
In which two main ways are proteins embedded in the phospholipid bilayer of the cell-surface membrane?
Extrinsic proteins - occur on the surface or only partly embedded in it but never completely across it. They act to give mechanical support or in conjunction with glycolipids as cell receptors for hormones.
Intrinsic proteins - completely span the phospholipid bilayer from one side to the other. Some act as carriers to transport water-soluble material across the membrane and others are enzymes.
What is the function of the proteins in the cell-surface membrane?
Provide structural support
Act as carriers transporting water-soluble substances across the membrane
Allow Clive transport across the membrane by forming ion channels for sodium, potassium etc
Form recognition sites by identifying cells
Help cells adhere together
Act as receptors e.g for hormones
What is the arrangement of phospholipids and proteins called in the cell-surface membrane?
The fluid-mosaic model