biology-they could ask you to compare these...

cellulose-- polysaccharide
glycogen- polysacharide

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starch- the energy storage in plants

consits of a mixture of long straght chain amylose molecules and branched amylopeptin. in plant is a mixture of both amylose and amylopeptin.
-stored in chloroplast and elsewhere in the plant cell in membrane bound starch grains.
-starch can be broken down to glucose molecules which may then respire to release energy.
-dont disolve in water as it made up of thousands of large a-glucose molecules therefore the stored glucose doesnt effect the water potential of the cell= vital feature in plants as glucose store stored in a cell as free molecules would dissolve and dramatically reduce the water potential. 
- joined by a condensation reaction.- forms grains/granules

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glycogen-energy storage in animals

-sometimes refered to as animal starch.
-made of large a-glucose. can be broken to release the glucose to be respired.
- differs from  starch because the 1-4 glucose chains in glycogen tend to be shorter + have many more branches extending from its chain- means glycogen is more compact then starch and forms glycogen granules in animal cells 

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cellulose- helps form/support cell wall

fibres are arrange in specific way to form the cell wall.
- large molocules of many b-glucose joined by condensation reactions-insouble inwater and is very  strong.
- glucose monomers contain many OH groups many hydrogen groups form between them.
-about 60-70 cellulose molocules become crosslinked by hydrogen bonds to form bundles called microfibrils.
--> these are held together by more hydrogen bonds to form larger bundles called macrofibrils- have great mechanical strength- almost like steel. they are embedded in polysaccaride glue of substances called pectins to form cell walls.

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structure+ function of plant cell walls

- arrangement  of macrofibrils allows water to move through and along cell walls and water can pass in and out of the cell easily.
- water moving into plant cells doesnt cause the cells to burst as it does in animals. it prevents it bursting and in turgid cells it helps to support the whole plant.
- arrangement of macrofibris in cell walls determines how cells can grow or change shape. e.g guard cell walls have arrangements of macrofibrils that result in the opening and closing of the stomata as water moves in or out of cells.
-cell walls can be reinforced with other substances to provide extra support or to make the walls waterproof.

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Globular proteins

roll up to form balls-usually soluble-usually have metabolic roles-
e.g enzymes found in all organisms-plasma proteins and antibodies found in the blood of mammels

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Fibrous proteins

forms fibres-usually insoluble- usually have structural roles-
e.g collagen found in bone and cartilage-keratin found in fingernails and hair

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Haemoglobin-a transport protein

its quaternary structure consists of 4 polypeptide subunits – 2 are called a- chains and other 2 are b-chains- 4 subunits together form one haemoglobin molecule form 1 haemoglobin molecule which is a water soluble globular protein.
- the tertiary structure of each subunit is held in place by a number of bonds and interactions which give the subunits and hence the complete molecule a very specific shape which is vital for the molecule to function.
- in this case its function is to carry oxygen from the lungs to the tissues. It binds o2 in the lungs and releases it in the tissues. A specialised part of each polypeptide called a haem group containing an iron FE+2 ion. The haem group is responsible for the colour of the haemoglobin.
- Haemoglobin+o2
purple-red                   bright red

-an oxygen molecule cans bing to the iron in the haem group= one complete haemoglobin molecules can bind up to 4o2 molecules.
- The haem group isn’t made up of amino acids- it is an essential part of the molecule-found in many proteins known as a prosthetic group

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Collegen- a structural protein

-fibrous protein- made up of 3 polypeptide chains wound around each other. Each of the 3 chains is itself a coil made up of around 100 amino acids. Hydrogen bonds form between the chains giving the structure strength.
- strength of molecule is increased further as each collagen molecule forms covalent bonds called cross links with other collagen molecules next to it. The cross links that form are staggered along the collagen molecules adding to the strength of the molecule- this result in a structure called a collagen fibril which together forms a collagen fibre.
- function is to provided structural strength for a no. of things:
-in the walls of arteries a layer of collagen prevents blood that is being pumped from the heart at high pressure from bursting the walls.
- tendons connect skeletal muscles to the bones- mostly collagen and form a strong connection that allows muscles to pull bones for movement.
cartilage and connective tissue are also made from collagen.     

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Differences between collagen and haemoglobin:

haemoglobin               collagen
globular                        fibrous

soluble in                     insoluble

wide range of             approx 35% of the molecules primary structure is one type of amino acid- glycine
amino acid
in primary structure

Contains a               doesn’t have a prosthetic group

Much of the       much of molecule consists for left- handed helix structure.
Molecule is
wound into alpha
helix structure

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consits of 1 glycerol molcule bonded to 3 fatty acid molocules- all joined in the same way- a condensation reaction between the acid group of fatty acid molocule and one of the OH groups of the glycerol molocule forms a colvelant bond.

new bond formed= ester. new molocule produced=monoglyceride. condensation reactions between acid groups of 2 more fatty acid molocules with the 2 remaining OH groups on the glycerol form triglyderide=.....................................
- insoluble inwater= hydrophobic. because the charges on the molocule  are distrubuted evenly around the molocule. this means that H bonds cant form with water molocules so the 2 types of molocules cannot mix.

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saturated or unsaturated?

term unsaturated often used when promoting healthier foods. To much saturated fat= poor diet. it refers to hydrocarbon chain and whether it is saturated with hydrogen or not. if all the possible bonds are made with hydrogen the fatty acid= saturated.

unsaturated fatty acids have c=c bonds- fewer H atoms can be bonded to the molcule. a single c=c double bond gives a mono unsaturated fatty acid.

introducing c=c double bonds changes shape of hydrocarbon chain- shape changes makes the molocule in a lipid push apart= making them more fluid. means lipids containing many unsaturated fatty acids are often oilds- those with mainly saturated fatty acids are often fats.

many animal lipids contain great deal of saturated fatty acids. they are solid at room temp- fats. many plant lipids contain unsaturated fatty acids. they are liquid at room temp and are called oils. animal lipid lard is solid but plat lipid olive oil=liquid.

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glycerol and fatty acids

glycerol and fatty acids are found in all the fats and oils thay perform roles in energy storage and supply+ those found in membranes. glycerol is always the same- fatty acid molcules found in lipids can differ. amino acids-animals cant make some of the fatty acids they need from the raw materials taken from thier bodies= essential fatty acids and they must be taken in complete as part of the diet.

fatty acids- similar but different
all fatty acids have acid group at 1 end- same as that found on amino acid- rest of molocule-hydrocarbon chains. hydrocarbon can be anything from 2-20 carbons long. fatty acids found most commonly have around 18 carbons in the hydrocarbon chain.

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essential oils-phospholipids-basis of biological m

almost idential to a triglycerid- but the 3rd fatty caid isnt added. instead a phosphate group is covalently bonded to the 3rd OH group on the glycerol. bonding of the phosphate group occurs by condensation reasction and so water molcule is released.

phosphate head is hydrophilic- hydrocarbon chain fatty acid tails are hydrophobic.  majority of a phospholipid is insoluble in water like all lipid molocules. water solubility of head group gives phosophlipids thier characteristics in terms of the capacity to form membranes.

phosophlipds and membrane fluidity
fatty acids that make up a phosopholipid may be saturated or unsaturated- organisms can control fluidity of membrane usuing this feature- e.g organisms in colder climates have increase no. of unsaturated fatty acids in thier phosopholipid molocules- ensures the membranes remain fluid despite low temp.  

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lipids and respiration-cholestrol+steriod hormones

respiration of lipids requires hydrolosis of ester bonds. both glycerol and fatty acids can then be broken down completely to co2 and h20.  this releases energy which is used to generate ATP molcules.
repsrtation of 1g of lipid gives about 2wice as much energy as the respiration of 1g og carbohydrate. because lipids are insoluble in water- can be stores in a compact way and dont effect water potential of cell content- makes triglyceride excellent energy storage. respiration of lipid gives out gr8 deal more water than the respiration of carbohydrates. this metabolic water is vital for some organisms.

cholesteral and steroid hormones.
cholesteral  form of lipid- not formed from fatty acids +glycerol. it is small molecule made form 4 carbon based rings. its found in all biological membranes- small narrow structure+ hydrophobic nature allow it to sit betweeen phospholipid hydrocarbon tails and help regulate the fluidity and strength of membrane.
steriod hormone testosterone,oestrogen and vitmin D are made from cholesteral. lipid nature of steriod Hormone means they can pass directly through phospholipid bilayer. this usually inside the nucleus so they also pass through the lipid bilayer of nuclear envelope.
cholestral is vital-many cells e.g liver can make it. excess cholesteral  is problem e.g:
-bile-cholestral can stick together making gallstones
- blood chloestreal can be depostied in inner linning of blood vessel-atherosclerosis.
hypercholesterolaemia is genetic disorder where cells manufacture+secrete cholesteral  even though there is already sufficent in the blood to provide for organism requirements. happens because the cells dont obey signal to stop cholesteral production as they lack cell surface receptors. - can suffer heart attacks and strokes by age of 2.

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