MODULES 1 and 2 Flashcards
What are prokaryotic organisms?
They are just one prokaryotic cell ( single cellular) Eg. bacteria
What are Eukaryotic organisms?
Made up of many eukaryotic cells (multi cellular) Eg. plants and animals
Differences between a plant and animal cell?
Plant has all organelles in an animal cell plus: Cell wall with plasmodesmata Vacuole Chloroplasts
Description and function of plasma (cell surface) membrane?
Found on surface of animal cells, and inside cell wall of plant cells and prokaryotic cells. Made up mainly of lipids and protein Regulates movement of substances in and out of the cell Has receptor molecules that allow it to respond to chemicals like hormones
Description and function of cell wall?
Rigid structure that surrounds plant cells it’s mainly made of cellulose Supports plant cells
Description and function of the nucleus?
A large organelle surrounded by a nuclear envelope (double membrane) which contains many pores Contains chromatin (made up from DNA and proteins), and a structure called the nucleolus Controls the cells activities by controlling the transcription of DNA DNA contains instructions to make proteins The pores allow substances to move between the nucleus and the cytoplasum The nucleolus makes ribosomes
Description and function of lysosomes?
A round organelle surrounded by a membrane Contains digestive enzymes which are kept separate from the cytoplasm by the surrounding membrane Used to digest invading cells or to break down worn out components of the cell
Description and function of a ribosome?
Very small organelle which either floats free in the cytoplasm, or is attached to the rough endoplasmic reticulum Site where proteins are made
Description and function of Rough endoplasmic reticulum?
A system of membranes covered with ribosomes Folds and processes proteins which have been made at the ribosomes
Description and function of smooth endoplasmic reticulum?
Similar to RER except no ribosomes Synthesises and processes lipids
Description and function of a vesicle?
Small fluid filled sac in the cytoplasm surrounded by a membrane Transports substances in and out of the cell
Description and function of the golgi apparatus?
Fluid filled membrane bound flattened sacs Processes and packages new lipids and proteins Also makes lysosomes
Description and function of a mitochondrion?
Have a double membrane Inner one is folded to form cristae Inside is the matrix which contains enzmyes for respiration Site of aerobic respiration and where ATP is produced
Description and function of a choroplast?
Surrounded by a double membrane, and has membranes inside thylakoid membranes, which stack into grana Grana are linked together by lamellae Site of photosynthesis
Description and function of centrioles?
Small hollow cyclinders made of microtubules Involved in seperation of chromosomes
Description and function of Cilia?
Hair like substances found on the surface membrane of some animal cells Cross section has a ring of 9 pairs of protein microtubules inside with a pair in the middle aswell Allows movements of substances on the cell surface
Description and function of a flagellum?
Like Cilia except longer Propels cells
How are organelles involved in protein production?
Proteins are made at the ribosomes The Ribosomes on the rough endoplasmic reticulum make proteins that are excreted or attached to the cell membrane New proteins produced at the rough endoplasmic reticulum are folded and processed (sugar chains added) by the rough endoplasmic reticulum Then they are transported from the rough ER to the golgi apparatus in vesicles At the golgi apparatus the proteins undergo further processing Proteins enter more vesicles and are secreted out of the cell
What is the cytoskeleton of a cell?
Network of protein threads running through a cell, arranged as microfilaments (small solid strands) and microtubules (tiny protein cylinders)
4 Main functions of the cytoskeleton?
The microtubules and microfilaments support the cell’s organelles, keeping them in position. Helps strengthen the cell and maintain it’s shape Responsible for movement of materials within the cell, eg. chromosomes when they separate during cell division, relies on contraction of microtubules in the spindle Can cause the cell to move, eg in cillia or flagellum
How does a prokaryote’s cell size comapare to a eukaryote’ss cell size?
prokaryote’s cell size is very small (less than 2 um diameter Eukaryotes much larger, (10-100 um)
What’s the DNA like in a prokaryote’s cell compared to a eukrayotes cell?
prokaryote’s cell DNA is circular, whilst a eukaryotes is linear
Where is the DNA found in a prokaryote’s cell compared to a eukaryotes cell?
In a prokaryote’s cell there is no nucleus, so DNA is free in the cytoplasm Whereas in a eukaryote, nucleus is present so it’s found within the nucleus
What’s the cell wall in prokaryote’s cell like compared to a eukaryotes cell?
In a prokaryote’s cell it’s made of a polysaccharide, but not cellulose or chitin No cell wall in animal cells, cellulose in plants and chitin in fungi
How do the amount and type of organelles in a prokaryote’s cell compare to a eukaryotes cell?
In a prokaryote’s cell very few organelles and none are membrane bound In a eukaryotes cell, many membrane bound organelles present
How do the ribosomes differ in a prokaryote’s cell compared to a eukaryotes cell?
Small ribosomes in a prokaryote’s cell, and larger ribsomes in a eukaryotic cell
Structure of a bacterial cell?
Flagellum to propel cell DNA (bacterial chromosome) Plasmid (ring of DNA) Plasma membrane Cell wall Ribosomes
Magnification definition and formula?
How much bigger the image is than the specimen Magnification = image size / object size
Resolution definition?
How well a microscope can distinguish between 2 points that are really close to each other
How to convert between mm, um and nm?
mm = 1m x 10^-3 um= 1m x 10^-6 nm= 1m x 10^-9
Features of a light microscope?
Uses light Have lower resolution that electron microscopes (0.2um) Maximum magnification of a light microscope is x1500
Features of a scanning confocal microscope?
Use laser beams on a specimen tagged with fluorescent dye Laser causes dye to fluoresce, which is directed through a pinhole onto a detector connected to a computer which can produce a 3D image Pinhole creates a clearer image, as all out of focus light is blocked Can look at specimens at different depths
Features of a transmission electron microscope?
Uses electromagnets to focus a beam of electrons which is transmitted through the specimen, in which denser parts of the specimen absborb more electrons, which then appear darker in the image Only work on thin specimens Resolution of 0.0002 um Magnification of more than 1,000,000
Features of a scanning electron microscope?
Scans a beam of electrons across the specimen, knocking electrons off, which are collected in a cathode ray tube to form an image. Image can be 3D Resolution 0.002 um Magnification x 500,000
Using a light microscope, how do prevent the problem of the sample being transparent so the electrons pass straight through?
Can stain the sample, different parts take more up than others the contrast makes different parts show up
How do you stain samples for an electron microscope?
Objects are dipped into a solution of heavy metal, the metal ions scatter the electrons creating contrast again
How do you prepare a dry mount?
Use tweezers to put specimen on a slide, and put a cover slip on top
How do you prepare a wet mount?
Pipette a small drop of water onto the slide, use tweezers to put your specimen on top of water drop Put a cover slip on avoiding air bubbles Add a stain to one side of your specimen and put paper towel opposite side to draw it in
How do you find the value of each eye piece unit of an eyepiece graticule?
Use a stage micrometer, to measure what eyepiece unit is worth, need to re calibrate for different magnifications
Functions of water inside and outside of cells?
Water is a reactant in many important chemical reactions It’s a solvent, so allows biological reactions to take place in solution Water transports substances, liquid and a solvent so very useful can transport substances such as glucose and oxygen Helps temperature control as has a high specific heat capacity and high latent heat of evaporation It’s a habitat`
Why is water a polar molecule and what does this allow it to do?
Oxygen has a higher electronegativity than hydrogen, so attracts the electrons more making the oxygen delta negative, and the hydrogen’s delta positive Hydrogen bonding, as the delta positve hydrogen’s are attracted to the delta negative electrons of other water molecules
How can hydrogen bonding give water a high specific heat capacity?
Specific heat capacity is the energy required to raise the temperature of 1 gram of substance by 1 degree Hydrogen bonds between water molecules can absorb a lot of energy, meaning water requires a lot of energy to heat up Meaning it has a very stable temperature
How do hydrogen bonds give water a high latent heat of evaportation?
Hydrogen bonds mean that it takes a lot of energy to break the intermolecular forces between water molecules, so a lot of energy used up when water evaporates Good for cooling organisms, as when sweat evaporates it cools the surface of the skin
What’s cohesion and why are water molecules very cohesive and what does this help them do?
Is the attraction water molecules of the same type Occurs in water molecules as they are polar Helps them flow so they are good for transporting substances
How does water’s polarity make it a good solvent?
It can dissolve salts as the delta positively charged hydrogen’s will surround the negatively charged ions, and the delta negative oxygens will surround the positively charged ions, seperating out the salt causing it to dissolve
Why is water less dense when it is a solid?
Water molecules are held further apart in ice than they are in liquid, because each water molecule forms 4 hydrogen bonds to other water molecules making a lattice shape This is why ice floats
Why is ice floating useful to living organisms?
Ice acts as an insulating layer on top of the water, so the water bellow doesn’t freeze killing the living organisms
Most carbohydrates are polymers, what’s a polymer?
A molecule made up of many similar, smaller monomers bonded together
Structure of glucose?
It’s a hexose ( 6 carbon) monosaccharide Alpha glucose: starting at top right then going clockwise C1 bonded to CH2OH O C2 bonded to H above and OH bellow C3 bonded to H above and OH bellow C4 bonded to OH above and H bellow C6 OH bellow and H above Beta: the same as alpha, except on C2 OH is above, and H is bellow
How is glucose’s structure related to it’s function?
It’s the main energy source in animals as it’s structure makes it soluble, so can be transported easily, and it’s chemical bonds contain a lot of energy
What’s ribose?
Monosaccharide with five carbon atoms so it’s a pentose sugar Structure starting from Top of pentagon: O C1 OH above and H bellow C2 H above and OH bellow C3 H above and OH bellow C4 H bellow and CH2OH above
What elements do carbohydrates consist of?
Carbon Oxygen Hydroged
How do 2 monosaccharides bond together?
Via a condensation reaction A hydrogen atom from one monosaccharide binds to the OH group of another monosaccharide releasing a molecule of water, and forming a glycosidic bond (both molecules binded to each other by an oxygen) This a condensation reaction Forms a disaccharide
What’s the reverse of a condensation reaction?
A hydrolysis reaction, water is removed to split a molecule
What does the disaccharide maltose consist of?
2 molecules of alpha glucose binded to each other via a glycosidic bond
What does the disaccharide sucrose consist of?
When alpha glucose and fructose join together via a glycosidic bond
What does the disaccharide Lactose consist of?
When Beta glucose is bonded to galactose
What’s a polysaccharide?
When more than 2 monosaccharides join together
What do plants store excess glucose as?
Starch, when a plant needs energy breaks it down into glucose
What does starch consist of?
A mixture of the 2 polysaccharides of alpha glucose amylose and amylopectin
Describe the structure of amylose?
A long unbranched chain of alpha glucose. The angles of glycosidic bonds give it a coiled structure Condense structure makes it good for storage as can fit more into a smaller space
Describe the structure of amylopectin?
A long branched chain of alpha glucose, it’s side chains allow the enzymes that break down the molecule to get at the molecule to break the glycosidic bonds. So glucose can be released quickly
How do animal cells store glucose?
Store it as glycogen, another polysaccharide of glucose
Structure of glycogen?
Polysaccharide of alpha glucose, similar to amylopectin, except that it has far more side branches coming off it, so energy can be released more readily, which is good for animals
Why is it useful that starch is insoluble in water?
Means it doesn’t cause water to enter cells via osmosis, which would make them swell
Describe the structure and function of hydrogen bonds?
Long unbranched chains of beta glucose, the cellulose chains are linked by hydrogen bonds to form strong fibres called microfibrils The strong fibres provide strucutral support for the cell, eg. in plant walls
Explain the general structure of a triglyceride?
Glycerol bonded to 3 fatty acid chains Fatty acid chains are made of hydrocarbons (compounds that only contain hydrogen and carbon) The tails are hydrophobic, meaning the tails are insoluble in water
What elements do lipids contain?
Carbon, Oxygen and Hydrogen
How are triglycerides synthesised?
By the formation of an ester bond between each fatty acid and the glycerol molecule A condensation reaction occurs, between the OH group on the glycerol (prop-tri-ol) and the OH of the carboxylic group at the end of the hydrocarbon chain.
What’s the process of synthesising a triglyceride called?
Esterfication
What’s the type of reaction called which breaks down a triglyceride?
Hydrolysis
What’s a saturated fatty acid?
Hydrocarbon chain containing no double carbon carbon double bonds (saturated with hydrogen)
What’s an unsaturated fatty acid?
Hydrocarbon chain which has at least one carbon carbon double bond, causing it to kink
Structure of phospholipids?
The same as a triglyceride, except missing a fatty acid chain, in replace for a phosphate group in the other direction. The phosphate group is hydrophillic (attracted to water) and the and the fatty acid chains are hydrophobic
Why are triglycerides good energy storage molecules in animals and plants?
The hydrocarbon tails contain a lot of chemical energy when they are broken down They are insoluble, so don’t affect water potential of cell, causing water to move in via osmosis, they are insoluble as Triglycerides bundle together as insoluble droplets, as glycerol shields hydrophobic fatty acid chains as they all face inwards to form a sphere
Describe the structure and function of a phospholipid bilayer?
Formed from a double layer of phospholipids, tails facing inwards as hydrophobic and phosphate heads facing outwards as hydrophillic Centre of the bilayer is hydrophobic, preventing water soluble substances passing through
What are the monomers of proteins?
Amino acids
What is a dipeptide?
When 2 amino acids join together
What is a a polypeptide?
When more than 2 amino acids join together
What are proteins made up of?
One or more polypeptides
General structure of an amino acid?
Carbon in centre Amine group to the left (NH2) Carboxylic group to the right (COOH) Hydrogen bellow R group above
What separates all amino acids?
They have different R groups
How are amino acids joined together?
A condensation reaction occurs between the OH of the Carboxylic group and the H of the amine group, removing water and forming a peptide bond
How do you split 2 amino acids?
Via a hydrolysis reaction
What’s the primary structure of a protein?
The sequence of amino acids in the polypeptide chain
What’s the secondary structure of a protein?
When hydrogen bonds form between nearby amino acids This makes it coil into an alpha helix, or fold into a beta pleated sheet, this is the secondary structure
What’s the tertiary structure of a protein?
The coiled or folded chain of amino acids is often coiled and folded further. More bonds form between different parts of the polypeptide chain, forming their final 3D structure
What’s the Quaternary structure of a protein?
When a protein is made of several different polypeptide bonds held together by bonds, the quartenary structure is the way these polypeptide chains are assembled together Eg. haemoglobin is made up of 4 polypeptide chains
What bonds are present in the primary structure of a protein?
Peptide bonds
What bonds are present in secondary structure?
Hydrogen bonds
What bonds are present in tertiary structure?
Ionic bonds between negatively charged R groups, and positively charged charged R groups Disulfide bonds, forms between 2 amino acids of csyteine, as it’s sulphur containing Hydrophobic and hydrophillic interactions Hydrogen bonds
What elements do proteins contain?
All contain Oxygen, Hydrogen, and Nitrogen Some contain sulphur
Structure of a globular protein?
Hydrophillic R groups on the outside, making them soluble, so they’re easily transported in fluids
Structure and function of the globular protein haemoglobin?
Carries oxygen around the body in red blood cells It’s a conjugated protein meaning it’s a protein with a non protein group attached (prosthetic group) So each prosthetic group has a prosthetic group called haem, which contains iron, which oxygen binds to
Structure and function of the lipid cholesterol?
Has a hydrocarbon ring structure, attached to a hydrocarbon tail. The ring structure has a polar hydroxyl OH group attached to it Helps strengthen the cell membrane, by interacting with the phopholipid bilayer Has a small size and flattened shape, so can fit in between the phospholipid molecules in the membrane They bind to hyrophobic tails of the phospholipids, causing them to pack together more closely, this helps the membrane be less fluid and more rigid
Structure and function of the globular protein insulin?
Hormone secreted by the pancreas, helps regulate blood glucose level. Solubility important, as it can be transported in the blood to the tissues where it acts Consists of 2 polypeptide chains which are held together by disulphide bonds
Structure and function of the globular protein amylase?
Enzyme, that catalyses the breakdown of starch in the digestive system Made of a single chain of amino acids, it’s secondary structure contains both alpha helix, and beta pleated sheets
3 Types of fibrous proteins?
Collagen Keratin Elastin All insoluble, strong and structural
Structure and function of the fibrous protein collagen?
Found in animal connective tissue (bone, muscle) Very strong, minerals can bind to increase it’s rigidity
Structure and function of the fibrous protein keratin?
Found in external structures of animals, eg skin, hair and nails Can be flexible or very tough
Structure and function of elastin?
Found in elastic connective tissue, such as skin and large blood vessels Elastic so allows tissues to return to their original shape after being stretched
What’s an ion with a positive charge called?
Cation
What’s an ion with a negative charge called?
Anion
What does the inorganic ion Ca2+ do?
Involved in the transmission of nerve impulses Involved in release of insulin from pancreas Acts as a cofactor for many enzymes Important for many enzymess
What does the inorganic ion Na+ do?
Important in generating nerve impulses for muscle contraction Regulating fluid balance in the body
What does the inorganic ion K+ do?
Important in generating nerve impulses for muscle contraction Regulating fluid balance in the body Activates essential enzymes needed for photosynthesis
What does the inorganic ion H+ do?
Affects the pH of substances Important for photosynthesis reactions that occur in the thylakoid membranes inside chloroplasts
What does the inorganic ion NH4+ do?
Absorbed from soil by plants as an important source of Nitrogen
What does the inorganic ion NO3 - (nitrate) do?
Absorbed from soil by plants, and is an important source of Nitrogen
What does the inorganic ion HCO3- (hydrogen carbonate) do?
Acts as a buffer, which helps maintain the pH in the blood
What does the inorganic ion Cl- do?
Involved in the chloride shift, which helps maintain the pH of the blood during gas exchange Acts as a cofactor for amylase
What does the inorganic ion PO4(3-) do?
Involved in photosynthesis and respiration reactions Needed for synthesis of nucleotides
What does the inorganic ion OH- do?
Affects the pH of substances
What are reducing sugars?
All the monosacchardies, and the disacharides maltose and lactose
How do you test for a reducing sugar?
Add benedict’s reagent and heat, will go from blue to brick red The higher the concentration of the reducing sugar, the further the colour change
How do you test for a non reducing sugar?
If the test for the reducing sugar is negative, then add dilute HCl and heat in a water bath Nuetralise it with Sodium Now do the Benedict’s test again
What can be used to test for glucose?
Test strips
How can you test for starch?
Add Iodine dissolved in potassium iodide solution, if present, sample will change from browny orange to a dark blue/black colour
Can you test for proteins?
Use the Biruet test Solution needs to be alkaline, so add a few drops sodium hydroxide solution Add some copper sulphate solution, if it goes stays blue there’s no protein, if goes purple protein is present
How do you test for lipids?
The emulsion test Shake the substance with ethanol then pour into water Solution will go milky if a lipid is present
How do you use calorimetry to measure the concentration of a glucose solution?
Create glucose concentrations using dilution factor 2 on 40m/M to create a 20, 10, 5 and 2.5 and a negative control of water You will have added benedict’s reagent, so the higher the concentration gradient of glucose, the lower the absorbance as more benedict’s reagent used up, as will have also remove precipitate by centrifuging it Now create a calibration curve by plotting absorbance on y axis, and concentration on x axis (use red filter) Now can use graph to find link the absorbance of a solution with an unknown concentration, with it’s concentration
What’s a biosensor?
A device that uses a biological molecule such as an enzyme
How would you use paper chromatography to identify unknown amino acids?
Have a mobile phase, a liquid solvent which allows the amino acids to move Have a stationary phase, where the molecules can’t move eg chromatography paper Put concentrated dots of the amino acids at the end of the chromatography paper, put in solvent and they’ll move up the paper at different rates so they’ll seperate out Spray with ninhydrin spray, to make them purple so more visible Calculate the R value of each value (distance moved by amino acid/ distance moved by solvent) then compare R value with a data base to work out what amino acids they are)
Function of an enzyme?
To speed up metabolic reactions, by acting as a biological catalyst
An example of an intracellular enzyme (works within cells)?
The enzyme catalase breaks down hydrogen peroxide to harmless oxygen and water Hydrogen peroxide is the toxic by product of some cellular reactions, and can kill cells
2 Examples of extracellular enzymes (work outside cells)?
The enzyme Amylase is found in saliva and is secreted into the mouth by cells in the saliva gland, it catalyses the hydrolyses of starch into maltose The enzyme trypsin catalyses the hydrolysis of peptide bonds so breaks down large polypeptides. It’s produced in the pancreas, and secreted into the small intestine
What type of protein are enzymes?
Globular
What do enzymes have which makes them specific to certain molecules?
An active site with a specific shape, which is where the molecule binds to, so they have to be complementary
What level of structure determines the active site?
Tertiary structure
How do enzymes reduce activation energy and therefore speed up the rate of reaction?
When a substance binds to an enzyme, an enzyme substrate complex is formed, this then lowers the activation energy (amount of energy that needs to be supplied to the chemicals before the reaction will start) If 2 substrate molecules need to be joined, then attaching the enzyme holds them closer together, reducing any repulsion between the molecules so they can bind more easily If the enzyme is catalysing a break down reaction, fitting into the active site puts a strain on the bonds in the substrate, this strain means the substrate molecule breaks up more easily
Describe the lock and key model?
The substrate binds to the active site of the enzyme as complementary , and forms an enzyme substrate complex An enzyme product complex is then formed and products are released, leaving the enzyme unchanged after the reaction
What does the induced fit model add to the lock and key model?
That when the substrate binds to active site, the active site changes shape slightly to fit the substrate more closely
Explain the process of heating an enzyme up to denaturation?
Initially rate of reaction will increase, as the increase in thermal energy means an increase in kinetic energy, meaning molecules move faster so more frequent collisions and also more successful collisions, so more enzyme substrate complexes formed per unit time. However if temperature reaches a certain point, starts to denature. The rise in temperature makes the molecules vibrate more, which then starts to break bonds in tertiary structure (weakest to strongest). Causes tertiary shape to change, and enzyme and substrate are no longer complementary
What is the temperature coefficient (Q10)?
Shows how much the rate of reaction changes when there’s an incresase of 10 degrees Before the optimum enzymes have a value of around 2
What can a different pH do to the optimum, do to an enzyme?
H+ ions and OH- ions can disrupt the hydrogen and ionic bonds, causing the tertiary structure to change and therefore the active, decreasing the rate of reaction
What does increasing the enzyme concentration do?
Makes it more likely for a substrate and an enzyme to collide and for an enzyme-substrate complex, therefore increases the rate of reaction, but only up to a certain point as if there’s a limited amount of substrate
What’s the saturation point?
When adding more substrate doesn’t make a difference, as all the active sites are taken up
2 ways to measure the rate of an enzyme controlled reaction?
Measure how fast the product of the reaction appears, eg in the reaction of catalase on hydrogen peroxide, measure how much Oxygen is produced in an upside down cylinder in water Can measure the disappearance of substrate, eg the enzyme amylase catalyses the reaction of starch to maltose, so during the reaction can keep adding sample to pottasium iodide and iodine solution, untill it doesn’t go blue/black, then you know all starch has disappeared.
What’s a cofactor?
Non protein substance, that attaches to an enzyme allowing it to work
Example of a inorganic cofactor?
Chloride ion, helps amylase enzyme bind to starch Aren’t affected during the reaction
What can an organic cofactor be known as?
Coenzymes, usually are sources from vitamins
What do coenzymes do during a reaction?
They participate in the reaction, so are changed Often act as carries, moving chemical groups between different enzymes
What’s a cofactor known as if it’s tightly bound to an enzyme, and an example?
Prosthetic group, eg Zn(2+) in cabonic anhydrase (which catalyses the production of carbonic acid, from water and CO2)
Explain what a competitive inhibitor is and how it works?
They are molecules that have similar shape to that of substrate molecules They compete with the substrate molecules to bind to the active site, but no reaction takes place, so they block the place for the substrate to react
Explain what a non competitive inhibitor is and how it works?
Molecules that bind to the enzyme at the alosteric site Causes the active site to change the shape so the substrate molecules can no longer bind to it
What makes an inhibitor reversible or non reversible?
Reversible if they’re bonded via weaker bonds such as hydrogen bonds Irreversible if they are bonded via strong hydrogen bonds
Examples of enzyme inhibitors?
Some drugs, and metabolic poisions
How are metabolic pathways regulated by end-product inhibition?
Metabollic pathway is a series of connected metabolic reactions, so the product of the first reaction takes part in the second reaction, each reaction is catalysed by a different enzyme Many enzymes are inhibited by the product of the reaction they catalyse, this is known as product inhibition End product inhibition is when the final product of the metabolic pathway, inhibits an enzyme which acts earlier on in the pathway So when there’s too much of final product will inhibit an earlier enzyme more, preventing too much being made
Why are some enzymes sometimes synthesised as inactive precursor enzymes?
So they don’t damage the cells they are synthesised in
Functions of membranes at the surface of cells (plasma membranes)?
They are barriers between the cell and the environment They’re partially permeable and control what substances enter and leave the cell They allow recognition by other cells They allow cell communication
Functions of membranes within cells?
Compartmentalises organelles, acting as a barrier between the organelle and cytoplasm Can form vesicles to transport substances between different areas of the cell They control which substances enter, and leave the organelle Can be the site of a chemical reaction
What are cell membranes made up of?
Lipids (mainly phospholipids) Proteins Carbohydrates (usually attached to proteins or lipids)
Describe the basic structure of a cell membrane?
Phospholipid molecules form a continuous double layer (bilayer) Bilayer is fluid as phopholipids are continuously moving Cholesterol molecules are present in the bilayer Proteins scattered thoughout the bilayer (like tiles) Some proteins have carbohydrates attached = glycoproten Some lipids also have a polysaccharide chain attached = glycolipid
How do phopholipids form a barrier to dissolved substances?
They have a head and a tail, the head is hydrophillic (attracts water) and the tail is hydrophobic (repels water) They arrange themselves in a bilayer, heads on outside, tails on the inside The centre of the bilayer is hydrophobic, so the membrane doesn’t allow water-soluble substances through it, however does allow fat-soluble substances through
What cholesterol do to the membrane?
Fits between the phospholipids, and bind to the hydrophobic tails, causing them to pack more closely
