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Terms in this set (61)
What is covalent bonding?
Atoms share a pair of electrons to form a molecule
What is ionic bonding?
Ions with opposite charges attract each other to form electrostatic attraction called an ionic bond (weaker than covalent)
What is hydrogen bonding?
The negative region of a polarised molecule attracts the positive region of another, it is a weak electrostatic bond (individually weak)
What are characteristics of monosaccharides?
They are sweet-tasting and soluble
What is the general formula of monosaccharides?
What are examples of monosaccharides?
Glucose, galactose and fructose
What are isomers of hexose?
Alpha glucose and beta glucose
What is a reduction?
A chemical reaction involving the gain of electrons and hydrogen
What does a reducing sugar do?
Donates an electron to another chemical
How do you test for a reducing sugar?
Obtain 2cm3 of a food sample (and add water) and add Benedict's reagent and heat for 5 minutes, and the solution turns red
Glucose and glucose
Glucose and fructose
Glucose and galactose
How do monosaccharides join?
Via condensation reactions to form a glycosidic bond
How do you break a disaccharide?
Hydrolysis (add water)
What is the test for non-reducing sugars?
Have a negative reducing sugars test first, and then add dilute HCl to 2cm3 of the food sample, and put it in a water bath for 5 minutes (hydrolyse disaccharide). Add sodium hydrogen carbonate to neutralise. Add 2cm3 of Benedict's and put in a water bath for 5 minutes. Solution turns orange-brown if it's a non-reducing sugar
What are polysaccharides?
Polymers from monosaccharides, joined via condensation reactions
What are characteristics of polysaccharides?
Very large molecules that are insoluble, so good for storage
How do you test for starch?
Add 2cm3 of food sample to a test tube and add two drops of iodine and shake. If starch is present the sample turns blue-black
What is starch found in?
Plants, as small grains
What are characteristics of starch?
Made of chains of alpha glucose, it can be branched or unbranched, the unbranched chain is wound into a tight molecule making the molecule very compact
What's the main role of starch?
Why is starch good for energy storage?
It's insoluble so doesn't affect water potential, so water doesn't get drawn into cells by osmosis
It's large and insoluble so can't diffuse out cells
It's compact so a lot can fit in a small space
When hydrolysed it forms alpha glucose which is easily transported and used in respiration
The branched form has many ends which are acted on by enzymes simultaneously, so glucose monomers are released rapidly
What is glycogen found in?
Animals (and bacteria), as small granules
What's the main role of glycogen?
Major carbohydrate storage product
Why is glycogen good for storage?
It is insoluble so water isn't drawn in and it can't diffuse out of cells
It's compact so a lot can fit a small space
It's more highly branched than starch so has more ends acted on by enzymes simultaneously, which are broken down rapidly into glucose monomers which is used in respiration (animals have a higher metabolic rate than plants, so are more active)
What are characteristics of cellulose?
Made of beta glucose monomers forming long, straight, unbranched chains
Why is cellulose a good source of strength?
The chains run parallel to each other, cross linked by hydrogen bonds to add collective strength
The molecules are grouped to form microfibrils, which are grouped to form fibres to add strength
Why are plant cell walls rigid?
The cellulose means the cell doesn't burst as water enters. This exerts inward pressure which stops a further influx of water, causing it to be turgid and push against one another. This keeps stems and leaves turgid, giving the maximum surface area for photosynthesis
What are characteristics of lipids?
They contain C, O, H (proportion of O lower than carbs), insoluble in water and soluble in organic solvents
What is the role of lipids?
Energy source- oxidised to provide two times the energy as carbs of the same mass and release valuable water
Waterproofing- insoluble in water
Insulation- slow conductors of heat and below body surface they retain body heat (act as electrical conductors in myelin sheath)
Phospholipids- flexible membranes and transfer or lipid soluble substances across it
Protection- fat around delicate organs
What are triglycerides?
Three fatty acids combined with glycerol- each fatty acid forms an ester bond with glycerol in a condensation reaction
How is the structure of triglycerides related to their properties?
High ratio of energy storing C-H bonds to C atoms make it a good energy source
Low mass to energy ratio make it a good storage molecule, so lot of energy stored in a small space
Large and non-polar so insoluble in water, so doesn't affect osmosis in cells and the water potential of them
High ratio of H to O atoms, releasing water when oxidised so it's an important water source
What's the structure of phospholipids?
A fatty acid molecule is replaced by a phosphate molecule, so hydrophobic tail and hydrophilic head
How is the structure of phospholipids related to their properties?
Polar, so in aq environments form a bilayer in cell-surface membranes to form a hydrophobic barrier inside and outside the cell
'Heads' help to hold at the surface of cell-surface membranes
What is the test for lipids?
Add 2cm3 of sample and 5cm3 of ethanol in a dry and grease free test tube. Shake to dissolve the lipid and add 5cm3 of water and if lipid present, turns cloudy white
How many amino acids are there?
100, 20 occur naturally in proteins
What is the structure of amino acids?
Central C atom with four different chemical groups attached to it
Amino group (NH2)
Carboxyl group (COOH) acidic part
R (side) group- variety of different chemical groups
How does a peptide bond form?
Condensation reaction between OH of carboxyl group in one amino acid and H from amino group of another
What is the primary structure of a protein?
Sequence of amino acids determined by DNA
How important is shape in protein?
Shape determines function, change in amino acid can alter it
What is the secondary structure of proteins?
The polypeptide chain is twisted into a 3D structure, due to hydrogen bonds between the NH and CO groups
What is the tertiary structure of proteins?
Alpha helices of secondary structure are twisted and folded to give a complex 3D structure
How is a tertiary structure maintained?
By three bonds
Disulfide bridges are strong, not easily broken
Ionic bonds between COOH and NH not involved in the peptide bond are weaker than disulfide bridges and are broken by changes in pH
H bonds are numerous but easily broken
How is the 3D structure of proteins important to function?
The protein is distinctive and recognises and is recognised by other molecules and interacts with them in a specific way
What is the quaternary structure of proteins?
A combination of a number of different polypeptide chains
What is the test for proteins?
Equal volumes of test solution and sodium hydroxide in a test tube. Add a few drops of dilute copper (II) sulfate solution and mix gently. If it turns purple there are peptide bonds, otherwise it remains blue
What is the point of enzymes?
Act as catalysts, lowering the activation energy, so allow reactions to take place at lower temperatures like 37 degrees
What is the enzyme structure?
Active site made from a small number of amino acids
How does a substrate attach to the active site?
By bonds that temporarily form between the amino acid of the active site and groups on the substrate
What is the induced fit model?
The enzyme is flexible and moulds itself around the substrate. As the shape changes, the enzyme puts a strain on the substrate molecule which distorts bonds in the substrate, that lowers the activation energy to break the bond
What is the effect of temperature on enzymes?
As the temperature increases the kinetic energy increases, so the molecules move more rapidly and collide more often
What happens to enzymes if the temperature is increased a bit too much?
H and other bonds break, so the active site changes shape
What happens to enzymes if the temperature is too high?
Why is body temperature 37 degrees?
Other proteins denature at a higher temperature
What affect do pH changes have on enzymes?
Alters charges on amino acids that make the active site so the substrate can't bind, and the enzyme substrate complex can't form. It can cause bonds maintaining tertiary structure to break so the active site changes shape
What is the effect of enzyme concentration?
If there is an excess of substrate, increase enzyme concentration to increase the rate of reaction. Soon the enzyme is in excess so graph levels off
What is the effect of substrate concentration?
If enzyme concentration is fixed and substrate concentration increases, the rate of reaction increases. With excess of substrate, the graph levels off
What is enzyme inhibition?
It interferes with the functioning of the active site, so the activity of the enzyme
What is a competitive inhibitor?
Binds to the active site of an enzyme
What is a non-competitive inhibitor?
Binds to the enzyme at a position other than the active site
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