Carbohydrates

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What are the functions of carbohydrates?
They can be used to store and supply energy and can also be structural.
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What are the functions of proteins?
They are used for transport and structure; they're also the basic components of all enzymes, hormones, antibodies, haemoglobin, ribosomes and many more materials.
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What are the functions of lipids?
They are insulators and protection (shock absorption), part of cell membranes, and also act as a minor energy supply.
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What are the functions of water?
It is important in the formation of many molecules, and also metabolic reactions.
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What are the functions of nucleic acids?
They are made of nucleotides and form DNA and RNA.
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What are the functions of enzymes?
They are biological catalysts.
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What are carbohydrates?
They are a group of substances containing carbon, hydrogen and oxygen that are important in many biological processes to provide energy and build body structures.
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What is the formula for a carbohydrate?
C (H O)
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What are sugars made up of?
Either monosaccharides (single sugar units), disaccharides (two sugar units joined by a condensation reaction), or polysaccharides (long chains of sugar units).
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What is the formula of a monosaccharide?
(CH O)
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If n=3, the monosaccharide is:
triose (glyceraldehyde)
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If n=5, the monosaccharide is:
pentose (fructose, ribose)
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If n=6, the monosaccharide is:
hexose (glucose, galactose)
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Monosaccharides are used for:
energy and building blocks.
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What is the structure of a disaccharide?
They are formed from two monosaccharides joined by a glycosidic bond, which occurs through a condensation reaction.
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Which disaccharide is formed by joining glucose and glucose?
Maltose
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Which disaccharide is formed by joining glucose and galactose?
Lactose
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Which disaccharide is formed by joining glucose and fructose?
Sucrose
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What is the structure of polysaccharides?
They are polymers formed from many monosaccharides linked by glycosidic bonds.
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What are the three important examples of polysaccharides?
Starch (amylose and amylopectin), glycogen and cellulose.
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What are reducing sugars?
They can donate electrons to other chemicals; all monosaccharides and some disaccharides are reducing sugars.
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What is Benedict's Reagent?
It is an alkaline solution of copper sulphate. When heated with a reducing sugar it forms an insoluble red precipitate of copper oxide.
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How do we break polysaccharides into their monosaccharide components to test for sugars?
We can do this using hydrochloric acid.
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How do we test for starch?
Starch is easily detected using potassium iodide solution. The iodine in the potassium iodide changes colour when it meets starch - from yellow to blue black.
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What is an assay?
It is a calibration curve - we take readings using a colorimeter of solutions in which we already know the concentrations and plot these results on a graph.
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What is starch?
It is an insoluble store of glucose in plants formed from two glucose polymers, amylose and amylopectin.
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What is the structure of amylose?
It consists of alpha glucose joined by 1,4 glycosidic bonds in a spiral structure.
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What is the structure of amylopectin?
It consists of alpha glucose joined by 1,4 and some 1,6 glycosidic bonds in a branched structure.
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How is starch structure suited to energy storage?
It is insoluble, large, and compact; as well as this, the monomer is alpha glucose and amylopectin is branched.
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Why does being insoluble mean starch is suited to its function?
It means that the water potential of the cell isn't affected.
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Why does being large mean starch is suited to its function?
It does not diffuse out of cells.
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Why does being compact mean starch is suited to its function?
A lot of it can be stored in a small place.
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Why does the fact it is made up of alpha glucose mean starch is suited to its function?
It is easily transported and readily used in respiration.
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Why does the fact amylopectin is branched mean starch is suited to its function?
There are many ends that can be hydrolysed by enzymes simultaneously so that glucose is released rapidly.
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What is the structure of glycogen?
It is insoluble and consists of alpha glucose units joined by 1,4 and 1,6 glycosidic bonds which give it a branched structure.
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Why is glycogen a better store of energy than starch?
It is more highly branched than starch so more rapidly broken down into glucose - this is important as animals have a higher metabolic rate and therefore respire more than plants.
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Where is glycogen stored?
It is stored in the muscles and liver.
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Why is the mass of carbohydrate stored in animals relatively small?
Because fat is the main storage molecule in animals.
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What is cellulose?
A structural polysaccharide made of beta-glucose.
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What is the structure of cellulose?
It is made up of straight, unbranched chains in which every other glucose is inverted. These chains are stacked parallel on top of each other allowing hydrogen bonds to form cross-links between chains, strengthening the molecule.
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How is cellulose suited to its function?
It is made up of beta glucose, contains hydrogen bonds, and the chains group to form microfibrils which in turn group to form fibres.
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What is cellulose's function?
To provide support and rigidity.
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Why does consisting of beta glucose mean cellulose is suited to its function?
It forms long, straight, unbranched chains.
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Why does consisting of hydrogen bonds mean cellulose is suited to its function?
Cellulose chains run parallel to each other and are cross-linked with lots of hydrogen bonds which add collective strength.
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Why does consisting of fibres mean cellulose is suited to its function?
Chains are grouped to form microfibrils which are in turn grouped to form fibres. Grouping provides strength.
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Why is cellulose a major component of plant cells?
It prevents the cell wall from bursting when water enters via osmosis. It exerts an inward pressure that stops further influx of water. As a result, living plant cells are turgid and push against one another – makes non-woody parts of a plant rigid.
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Why is it vital that stems and leaves are kept upright?
It is important for maximum light gain for photosynthesis.
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What is a lipid?
The main groups of lipids are triglycerides and phospholipids. They contain carbon, hydrogen and oxygen (but the portion of oxygen is smaller than in carbs). They are insoluble in water but soluble in organic solvents like alcohols and acetone.
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What is one triglyceride made up of?
One glycerol molecule and 3 fatty acids.
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What are the bonds formed in a triglyceride?
The bonds formed are ester bonds.
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What are the roles of lipids?
1) A source of energy. 2) For waterproofing. 3) As insulation. 4) As protection.
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Why are lipids good as a source of energy?
When oxidised provide more than twice the energy as the same mass of carbohydrate. They also release valuable water.
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How are lipids used as waterproofing?
Plants and insects have waxy lipid cuticles. Mammals produce oily lipid secretions from glands in the skin.
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Why can lipids be used as insulation?
They are slow conductors of heat so retain body heat when stored under the skin. They also act as electrical insulators around nerve cells.
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How are lipids used as protection?
Fat is often stored around delicate organs and act as shock absorbers.
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What is the difference between saturated and unsaturated fatty acids?
Saturated fatty acids only contain C-C bonds; unsaturated fatty acids contain one or more C=C double bonds.
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What is the structural difference between saturated and unsaturated fatty acids?
Unsaturated fatty acids have kinks in their chains because of the double bonds; the more double bonds there are, the kinkier the chain.
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What does saturated fatty acid mean?
It means every carbon atom is bonded to as many hydrogen atoms as possible (i.e. no more can be added), meaning it is saturated with hydrogen.
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Where do we find saturated fatty acids?
They are mainly found in animal fats from meat and dairy products.
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Are saturated fatty acids solid or liquid at room temperature?
Saturated fatty acids can pack together to form solid fat at room temperature.
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Where do we find unsaturated fatty acids?
They are mainly found in vegetable oils, nuts and fish.
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Are unsaturated fatty acids solid or liquid at room temperature?
Unsaturated fatty acids do not pack together easily and form liquid oils at room temperature.
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What is the structure of a phospholipid?
It is the same as a triglyceride but one of the fatty acid molecules is replaced by a phosphate molecule. It has a hydrophilic head and a hydrophobic tail.
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What do phospholipids do when exposed to water?
They form a micelle or bilayer.
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How does the phospholipid's polarity relate to its function?
It allows lipid soluble substances to enter and leave the cell, prevents water soluble substances entering and leaving and to make the membrane flexible.
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How does the phospholipid's polarity relate to its function?
It forms a bilayer within cell membranes and thus a hydrophobic barrier is formed between the inside and the outside of the cell.
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How does the phospholipid's ability to combine with carbohydrates relate to its function?
It combines with carbs to form glycolipids which are important in cell recognition.
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What are the functions of proteins?
Enzymes, transport, movement, cell recognition, channels (membrane proteins), structure, hormones and protection (antibodies).
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What are the properties of proteins determined by?
The amino acid sequence.
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What are proteins and what are they made of?
They are long chains of amino acids made from carbon, hydrogen, oxygen, nitrogen and sometimes sulphur.
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How many amino acids are there?
There are 20 amino acids.
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What are the three groups in an amino acid?
NH3, CH+R and COOH
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What is the R group in an amino acid?
This is the variable group.
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The reaction to bond two amino acids is called a _______ reaction.
condensation.
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What is the bond between two amino acids called?
A peptide bond.
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What do we call several amino acids bonded together?
A polypeptide.
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What is the primary structure of protein described as?
The sequence of amino acids.
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What is the secondary structure of protein described as?
Within the long protein chains there are regions in which the chains are organised into regular structures known as alpha-helixes and beta-pleated sheets.
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What is the tertiary structure of protein described as?
The alpha-helixes and beta-pleated sheets fold in on themselves to form a 3D folded protein. These are held together by hydrogen bonds, ionic bonds, covalent bonds and polar interactions.
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What is the quarternary structure of protein described as?
The 3D arrangement of more than 1 tertiary protein held together by hydrogen bonds.
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Why are hydrogen bonds form in a protein's secondary structure?
The amino and carboxylic acid groups in the chain carry small amounts of charge, negative on the CO of the carboxylic group and positive on the NH of the amino group. These charges result in hydrogen bonds.
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What are the two types of protein?
Fibrous proteins (rarer than globular) and globular proteins.
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Name the properties of fibrous proteins.
Insoluble, structural and forms fibres. Some examples are collagen, keratin and haemoglobin.
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Name the properties of globular proteins.
Soluble, functional and rolls up into balls. Some examples are enzymes and antibodies.
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What is the test for proteins?
The Biuret Test: add pale blue Biuret solution to a sample and shake. If the solution turns purple, it contains protein.
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What is deamination?
Deamination converts the amino acids into urea which is then removed in the urine.
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Why can't animals store excess amino acids?
The amino group makes them toxic if too much is present - this has to be removed in the liver by deamination.
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What is the test for lipids?
The test for lipids is the Emulsion Test. Add the food sample to 2cm3 of ethanol and shake well. Then add water; if there are lipids present, a milky white emulsion will be formed.
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What is activation energy?
The minimum energy needed for a given chemical reaction to take place.
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What is a catalyst?
A substance which speeds up a rate of reaction but is not used up or changed itself.
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What is an enzyme?
They are biological catalysts that speed up the rate of reaction in the body. They are found all over the body, not just in the digestive system.
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What is the active site?
The area of catalytic activity of the enzyme.
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Why is the reaction an enzyme can catalyse specific and individual?
The shape of the active site is specific and individual to the substrate.
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How do enzymes work? (Lock and key theory)
Enzymes react with another molecule called the substrate. Each enzyme has its own special shape, with an active site, onto which the substrate molecules bind.
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How do enzymes work? (Induced fit hypothesis)
In the presence of the substrate, the active site of the enzyme may change slightly in order to select the substrate's shape.
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Enzymes have a high turnover number - what does this mean?
This means that they can convert many molecules of substrate per unit time. Therefore enzymes are very efficient.
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Why is there an activation energy?
It is needed to break the existing chemical bonds inside molecules.
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How do enzymes work in speeding up a chemical reaction?
They lower the activation energy of a reaction and so reduce the input of energy needed and allow reactions to take place at lower temperatures.
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What does a low temperature mean for the rate of reaction and why?
It means a low rate; enzymes have too little energy and move slowly. Few successful collisions between enzymes and substrates leads to low rate of reaction.
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What does an optimum temperature mean for the rate of reaction and why?
It means a high rate; enzymes have a lot of kinetic energy and move quickly. Lots of successful collisions between enzymes and substrates leads to high rate of reaction.
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What does a high temperature mean for the rate of reaction and why?
It means a low rate of reaction; heat breaks the hydrogen bonds maintaining the tertiary structure of the enzyme. The active site becomes denatured and the substrate no longer fits. No successful collisions leads to low rate of reaction.
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What does a too low/too high pH mean for the rate of reaction and why?
It means a low rate of reaction; the acidity/alkanity breaks the ionic and hydrogen bonds maintaining the tertiary structure of the enzyme. The active site becomes denatured & the substrate no longer fits. No successful collisions lead to a low rate.
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What does an optimum pH mean for the rate of reaction and why?
It means a high rate because many collisions between working enzymes and substrates means a high rate of reaction.
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What does a low substrate concentration mean for the rate of reaction and why?
It means a low rate because few substrate molecules limits the chance of successful collisions between enzymes and substrates.
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What does a high substrate concentration mean for the rate of reaction and why?
It means a high rate because more substrate molecules increase the chance of successful collisions between enzymes and substrates.
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Why are enzymes effective in small quantities?
They are not used up in the reaction and so can be reused repeatedly.
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What are competitive inhibitors?
These have a similar shape to the substrate; they bind to the active site of the enzyme and block the substrate from entering.
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What does it mean for competitive inhibitors if the substrate concentration is increased?
It will reduce the effect of the inhibitor as the more substrate molecules present, the greater the chance of finding active sites, leaving fewer to be occupied by the inhibitor.
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What are non-competitive inhibitors?
These bind to the enzyme (not in the active site because they are a different shape to the substrate) and change its shape; this occurs because it changes the bonding in the tertiary structure of the enzyme. This means the substrate no longer fits.
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What does it mean for non-competitive inhibitors if the substrate concentration is increased?
As the substrate and inhibitor molecules attach to different parts of the enzyme they are not competing for the same sites. The rate of reaction is therefore unaffected by substrate concentration because the substrate doesn't fit.
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