Carbohydrates, Proteins & Lipids Flashcards
Describe the structure structure of carbohydrates
- organic compounds containing carbon, hydrogen and oxygen
- in carbohydrates the basic unit is a monosaccharide
- monosaccharide + monosaccharide = disaccharide
- many monosaccharides = polysaccharide
What are monosaccharides?
Small organic molecules and the building blocks for the larger carbohydrates
How many carbon atoms does a triose sugar have?
3
Define the term isomer
Same formula but different structural arrangement e.g alpha and beta glucose
Name some of the functions of monosaccharides
- source of energy
- building blocks for larger molecules
- intermediates for reactions
- constituents of nucleotides
What are disaccharides?
Two monosaccharide units bonded with the formation of glycosidic bind and the elimination of water
Glucose + glucose =
Glucose + fructose =
Glucose + galactose =
Maltose
Sucrose
Lactose
What is the test for reducing sugars?
Benedict’s test
How do you carry out the Benedict’s test for reducing sugars?
1) add equal volumes of the reagent to the solution
2) boil
3) colour change from blue to brick red
Test for non reducing sugars
1) add solution to HCL
2) boil
3) neutralise with alkali (sodium hydrogencarbonate)
4) add Benedict’s reagent
5) colour change from blue to brick red
What is another way to detect sucrose?
1) add sucrase enzyme
2) hydrolysed sucrose into glucose and fructose
3) add Benedict’s reagent
What are polysaccharides?
Large complex polymers formed from large numbers of monosaccharide units
Why is glucose converted to starch?
- insoluble so has no osmotic effect
- cannot diffuse out of the cell
- compact molecule that can be stored in a small space
What are the two polymers that starch is made up of?
Amylose and amylopectin
What is the structure of amylose?
- linear, unbraced
- alpha 1,4 glycosidic bonds
- this is repeated forming a chain which coils into a helix
What is the structure of amylopectin?
- 1,4 & 1,6 glycosidic bonds
- branched
What is the test for starch called?
Iodine test
How do you test for starch?
1) add iodine
2 colour change from brown to blue/black
What is the main storage in animals?
Glycogen
Describe the structure of glycogen?
- alpha 1,4 and 1,6 glycosidic bonds
- more branched than amylopectin
Where is cellulose found?
Plant cell walls
Describe the structure of cellulose
- long parallel chains of beta glucose
- better 1,4 glycosidic bonds
- adjacent glucose molecules rotated 180 degrees
- hydrogen bonds form
- molecules become tightly crosslinked to form microfibrils
- bundles of microfibrils = fibres
Where in chitin found?
- exoskeleton of insects
- fungal cell walls
Describe the structure of chitin
- beta 1,4 glycosidic bonds
- adjacent molecules rotated 180 degrees
- long parallel chains
- linked together by hydrogen bonds forming microfibrils
What are groups derived from amino acids added called?
Heteropolysaccharides
What do elements lipids contain, briefly describe their relative proportions?
Carbon, hydrogen and oxygen
But in proportion to carbon and hydrogen they contain much less oxygen
Describe some properties of lipids
- non poplar
- insoluble on water
- dissolve on organic solvents (such as proanone and alcohols)
How are triglycerides formed?
1 glycerol molecule and 3 fatty acid molecules join together during a condensation reaction and 3 molecules of water are removed and ester bonds are formed
What is an ester bond?
An oxygen atom joining two atoms one of which is a carbon atom attached by a double bond to an oxygen atom
What is an unusual property of phospholipids?
Each molecule has one end that is soluble in water, (in the glycerol group, the phosphate and the choline and so has a lot of oxygen atoms)
What part of a phospholipid is hydrophilic?
The phosphate group
What does a phospholipid consist of?
1 Glycerol molecule + 2 fatty acid molecules
- (this is the polar head of the molecule)
Why are the fatty acid tails non-polar?
The fatty acid tails do not have any oxygen atoms and do not interact with water so they are hydrophobic and non-polar
What are waxes?
Lipids and melt above 45°.
- they have a waterproofing role in both animals, such as insect exoskeleton and plants, in the leafs cuticle
Define saturated
- If the hydrocarbon chain has only single carbon-carbon bonds
- all the carbon atoms are linked to the maximum possible number of hydrogen atoms
Describe the structure and state of saturated lipids
- the fatty acid chain is a straight zig-zag
- the molecules can align readily so the fats are solid
- remain semi-solid at body temperature and so are useful for storage in mammals
•animal lipids often contain saturated fatty acids
Define unsaturated
- if any carbon-carbon bond is not a single bond
- not bonded to maximum number of hydrogen atoms
Describe the structure and shape of unsaturated lipids
- the molecules cannot align uniformly
- the lipid does not solidify readily
- unsaturated lipids are oils which are liquid at room temperature
•plant lipids are often unsaturated and occur as oils
What is a monounsaturated lipid?
If a lipid contains many carbon-carbon double bonds it is called?
- a lipid with one carbon-carbon double bond
- polyunsaturated
Roles of Phospholipids: (BE)
- In BIOLOGICAL MEMBRANES
* ELECTRICAL INSULATION- the myelin sheath that surrounds the axons of nerve endings
Roles of Triglycerides: (MPET)
- METABOLIC WATER-water released during chemical reactions in the body (triglycerides produce a lot of metabolic water when oxidised)
- PROTECTION-fat is often stored around delicate internal organs (e.g. The kidneys) to protect against physical damage
- ENERGY RESERVES-in both plants and animals because lipids contain more carbon-hydrogen bonds than in carbohydrates
- THERMAL INSULATION-when stored under the skin lipids insulate against heat loss in the cold or head gain when it’s very hot
Roles of Waxes: (W)
• WATERPROOFING-in terrestrial organism, waxes reduce water loss such as in the insect exoskeleton and in cuticle of plants
Test for fats and oils- the emulsion test
1) the sample is mixed with ethanol (it dissolves any lipids present
2) it is shaken with equal volumes of water
3) the dissolved lipids come out of solution because they are insoluble I water
4) they form an emulsion making the sample cloudy white
What are the main causes of heat disease?
- fatty deposits in the coronary arteries (atherosclerosis)
- high blood pressure (hypertension)
- a diet high in saturated fats
- smoking
- lack of exercise
- ageing
How are lipoproteins made?
When food has been absorbed at the small intestine lipids and proteins combine to make lipoproteins which travel around the body in the bloodstream
What happens if your diet is high in saturated fats ?
- (LDL) build up and cause harm
- fatty material (atheroma) gets deposited in the coronary arteries restricting blood flow therefore oxygen delivery to the heart
- can result in angina and if the vessel is completely blocked a myocardial infarction of heart attack occurs
What happens if your diet has a high proportion of unsaturated fats?
- the body has a high proportion of HDL which carries harmful fats away to the liver for disposal
- the higher the proportion of HDL to LDL in a persons blood the lower their risk of cardiovascular and coronary heart disease
How do proteins differ from carbohydrates?
- In addition to carbon, hydrogen and oxygen they always contain nitrogen
- many proteins also contain sulphur and some contain phosphorus
Proteins are polymers made of monomers called…
Amino acids
What are the chains of amino acids called?
Polypeptides
Around how many amino acids are used to make up proteins?
20
The proteins shape is determined by…
The specific sequence of amino acids in the chain
Describe the basic structure that all amino acids have
- Amine group-NH2 at one end of the molecule called N terminal
- Carboxyl group-COOH at the other end of the molecule called the C-terminal
- A hydrogen atom
- R group (which is different in each amino acid)
The amino group is alkaline, acidic or basic?
Basic
How does a zwitterion form?
- The amino group is basic
- At pH7, the pH of the cell it gains a H and becomes positively charged
- the carboxyl group is acidic and at pH7 it looses an H becoming negatively charged
- this is a zwitterion
How does a peptide bond form?
The amino group of one amino acid e
Reacts with the carboxyl group of another with the elimination of water. The bond that is formed from the condensation reaction is a peptide bond and the resulting compound is a dipeptide
Describe the primary structure of proteins:
•the order of amino acids in a polypeptide chain
- can be joined together in any number order and combination so there are many possible polypeptide
- the primary structure is determined by the base sequence on one strand of the DNA molecule
Describe the secondary structure of proteins:
•the shape that the polypeptide chain forms as a result of hydrogen bonding in the peptide bonds along the chain
- causes long polypeptide chain to be twisted into a 3D shape
- coils/ spirals to form alpha helix or folds to form beta pleated sheet
-
Secondary structure of Keratin
Secondary structure of silk
- keratin has a high proportion of alpha helix
- silk has a high proportion of beta pleated sheet
Describe the tertiary structure of proteins:
• further folding of the secondary structure into a more complex 3D shape which is maintained by:
- hydrogen bonds
- ionic bonds
- disulphides bridges
- hydrophobic interactions
Describe the quaternary structure of proteins:
- Many polypeptide chains joined together
- they many be associated with non-protein groups and form large complex molecules such as haemoglobin
What are the two main types of proteins?
Globular & Fibrous proteins
Are fibrous proteins soluble in water?
No they are insoluble
Describe the shape of fibrous proteins
- Fibrous proteins have Long, thin molecule
- the polypeptides are in parallel chains or sheets with many cross-linkages forming long fibres e.g keratin
What kind of functions do fibrous proteins have?
Structural functions e.g in bone
Properties of fibrous proteins
Strong and tough
What is the fibrous protein in hair?
Keratin
What is collagens function?
To provide strength and toughness in tendons
Describe the structure of collagen
- A single fibre (sometimes called tropocollagen) consists of three identical polypeptide chains twisted around each other like a rope
- the three chains are linked by hydrogen bonds making the molecule very stable
Describe the shape of globular proteins
Compact and folded into spherical molecules this makes them soluble in water
Give some examples of globular proteins
Enzymes, antibodies, plasma proteins and hormones
Describe the structure of haemoglobin
4 folded polypeptide chains at the centre of which is the iron containing prosthetic group (haem)
What is the test for proteins called?
The biuret test
Briefly describe how you would test for proteins
1) add a few drops of biuret reagent (sodium hydroxide and copper sulphate)
2) the sodium hydroxide and copper sulphate react to make copper hydroxide which interacts with the peptide bonds present in the protein to make biuret which is purple
Why is the test qualitative?
The more concentrated the protein the darker the purple colour
What is the problem at low protein concentrations
The colour is difficult to detect by eye
What could help you to overcome the problem of low protein concentration?
A colorimeter gives an estimate of relative concentration of proteins present in a sample
To detect the concentration of a specific protein, a biosensor would be required
