Topic 1

Question 1

What are monosaccharides?

Answer 1

simple sugars with the general formula (CH2O)n. They are reducing sugars (have the ability to reduce other molecules)

Question 2

What are triose sugars?

Answer 2

C3H6O3

important in mitochondria where glucose is broken down into triose sugars during respiration.

Question 3

What are pentose sugars? What is the structure of Ribose?

Answer 3

• C5H10O5

- e.g ribose and deoxyribose are important in nucleic acids DNA and RNA.

Question 4

What are Hexose Sugars? What is the structure of alpha and beta glucose?

Answer 4

C6H12O6

- e.g glucose, galactose and fructose.

Question 5

how is maltose formed. Where is it found?

Answer 5

α glucose + α glucose

Germinating seeds

Question 6

What are disaccharides?

Answer 6

These are two monosaccharides joined together by a condensation reaction producing a glycosidic bonds. They can be split through hydrolysis.

Question 7

How is lactose formed? Where is it found?

Answer 7

α glucose + β galactose.

Sugar in milk

Question 8

How is sucrose formed? Where is it found?

Answer 8

α glucose + fructose

plants e.g sugar cane

Question 9

What are polysaccharides?

Answer 9

these are made up of many repeating units of monosaccharides. (they are polymers)

Question 10

What is the form, structure and function of starch?

Answer 10

• made of two polymers of α glucose: amylose and amylopectin
• amylose: glucose molecules joined by α 1,4 glycosidic bonds. helix.
  Amylopectin: glucose molecules joined by α 1,4 glycosidic bonds BUT after every 25 adjacent chains are connected by α 1,6 glycosidic bonds e.g branched
• main storage polysaccharide in plants.
  insoluble in H2O therefore good storage compound e.g in stoma of chloroplasts.
  Helix forms compact shape allowing tight packing.
  many protruding ends can be hydrolysed rapidly- rapid release of glucose to provide energy.

Question 11

What is the form, structure and function of glycogen?

Answer 11

• polymer of α glucose.
• similar structure to amylopectin but has more branches which are shorter.
  very very compact.
• Main storage polysaccharide of animal and fungal cells.
  Structure allows faster hydrolysis than starch. as animals may need emergency glucose faster than plants.

Question 12

What is the form, structure and function of cellulose?

Answer 12

• polymer of glucose
• long unbranched chains of glucose linked by β 1,4 glycosidic bonds. individual chains linked by hydrogen bonds.
• structural polysaccharide in plants
  H+ bonding prevents H2O entering molecule hence resistant to enzyme hydrolysis making it good structural polysaccharide.

Question 13

What is a triglyceride?

Answer 13

Triglyceride: an ester derived from glycerol and three fatty acids. Triglyceride are the main constituents of body fat in animals as well as vegetable fat.

Glycerol + 3 fatty acids -> triglyceride + 3 H2O

When glycerol combines with 3 fatty acids a triglyceride forms. An ester bond is formed in a condensation reaction between the (-OH) of the glycerol and the (-COOH) of the fatty acids. A molecule of water is removed and the resulting bond is known as an ester bond.

Question 14

what is a saturated fatty acid?

Answer 14

saturated fatty acid: each carbon atom is joined to the one next to it in the hydrocarbon chain by a single covalent bond

Question 15

What is an unsaturated fatty acid?

Answer 15

unsaturated fatty acid: the carbon atoms in the hydrocarbon chain have one or more double covalent bonds in them.

Question 16

What are the functions of lipids?

Answer 16

energy storage: when lipids are oxidised in respiration, the bonds are broken and carbon dioxide and water are the ultimate products. This reaction can be used to drive the production of a lot of ATP. Lipids store about three times as much energy as the same mass of carbohydrates.

waterproofing: the hydrophobic nature of lipids allows them to be waterproof. Oils are important in waterproofing the fur and feathers of mammals and birds, while insects and plants use waxes for waterproofing their outer surfaces.

Insulation: insulating animals against heat loss. fatty sheath insulates nerves so electrical impulses travel faster.

Question 17

What is a phospholipid?

Answer 17

Phospholipid: a chemical in which glycerol bonds with two fatty acids and an inorganic phosphate group.

The phosphate is ionised and therefore soluble in water (polar)
The two fatty acid chains are insoluble in water (non polar)

The polar phosphate part is hydrophilic and dissolves readily in water. The lipid tails are hydrophobic so they do not dissolve in water. If the molecules are tightly packed in water they either form a monolayer, with the hydrophilic heads in the water and the hydrophobic lipid tails in the air. Or clusters called micelles, all the hydrophilic heads point outwards and all the hydrophobic tails are inside.

Question 18

What is the structure of amino acids? Diagram?

Answer 18

all amino acids have the same basic structure. There is always an amino group (-NH2) and a carboxyl group (-COOH) attached to a carbon atom. The R group varies between amino acids. The structure of the R group affects the way the amino acid bonds with others in the protein.

Question 19

What is a dipeptide and polypeptide?

Answer 19

amino acids join together in a condensation reaction between the amino group of one amino acid and the carboxyl group of another. A peptide bond is formed to join the amino acids together. When more and more amino acids join, a polypeptide is formed. When the polypeptide folds or associated with another polypeptide a protein is formed.

Question 20

what do hydrogen bonds do in proteins?

Answer 20

Hydrogen bonds: negative charges are present in the oxygen on the carboxyl group and positive charges are present on the hydrogen atoms of the amino groups. A weak hydrogen bond forms between two amino acids next to each other. These are important in the folding of polypeptide chains.

Question 21

What doe disulphide bonds do in proteins?

Answer 21

Disulphide bonds: These form when two cysteine molecules are close together in a polypeptide. They are important in holding the folded polypeptide chains in place.

Question 22

What do ionic bonds do in proteins

Answer 22

Ionic bonds:these from between the strongly positive and negative amino acid side chains found in protein molecules.

Question 23

Describe the structure levels of proteins. What bonds are used in each level?

Answer 23

Primary: Sequence of amino acids that make up the polypeptide chain. Peptide bonds.

Secondary: arrangement of polypeptide chain into regular repeating structure. Hydrogen bonds.

Tertiary: 3D folding of secondary structure. e.g globular proteins. Hydrogen, disulphide and ionic bonds.

Quaternary: 3D arrangement of more than one tertiary polypeptide. e.g haemoglobin. Hydrogen, disulphide and ionic bonds.

Question 24

What is the function, structure, solubility and examples of globular protein?

Answer 24

Function: varied function:
Hold molecules in position in the cytoplasm
immune system
form enzyme and some hormones that are involved in maintaining structure of cytoplasm.

Structure: Tertiary and sometimes quaternary.
Fold into spherical shapes.
Large.

Solubility: although they have ionic properties( carboxyl and amino ends) they are so big so do not dissolve in water but form collides.

Examples: antibodies and haemoglobin

Question 25

what is the function, structure, solubility and example of fibrous proteins?

Answer 25

Function: Structural function.
They appear in structures of connective tissue in tendons, strict of bones and silk of spiders webs.

Structure: Little or no tertiary structure.
Long parallel polypeptide chains with occasional cross linkages that form fibres.

Solubility: insoluble

Example: collagen and keratin (hair and nails)

Question 26

what is the structure of DNA?

Answer 26

DNA (deoxyribonucleic acid) is genetic material stored in the nucleus. nucleotides are the single unit of DNA. Containing sugar, phosphate and a base.

A strand of nucleotides are joined by covalent bonds. This gives a sugar phosphate backbone. Hydrogen bonds hold the base pairs together and also hold the structure of the double helix together.

Question 27

What are purines and pyrimidines?

Answer 27

Purines = double nitrogen ring. Adenine and Guanine.

Pyrimidines = single nitrogen ring. Thymine and cytosine.

Question 28

What is DNA replication and how does it occur?

Answer 28

DNA replication occurs in the S-phase of interphase, shortly before cell division. Each copies of all the DNA are made to enable production of two genetically identical daughter cells. DNA replication produces the sister chromatids which will be separated in anaphase of mitosis. Replication is semiconservative. (each new DNA molecule formed consists of one new strand and one old strand)

1. A portion of the DNA double helix is about to be replicated.
2. The enzyme DNA Helices moves along the DNA double helix unwinding and unzipping it by breaking the hydrogen bonds between the bases.
3. Free nucleotides are attracted to the exposed complementary bases. DNA polymerase aligns the free nucleotides and new hydrogen bonds form.
4. DNA ligase forms the sugar phosphate backbone forming phosphodiester bonds.
5. Replication is complete with two identical strands of DNA.

Question 29

What is the structure of mRNA?

Answer 29

The structure of mRNA is very similar to that of DNA. However the deoxyribose sugar is replaced with ribose sugar. Additionally thymine is replaced with uracil.

Question 30

What is the structure of tRNA?

Answer 30

Clover leaf shape.
The Anticodon; part of tRNA molecule, that has a sequence of three bases that are complementary to the bases in the mRNA codon.
Binding site: allows the tRNA to pick up one specific amino acid from the vast numbers in the cytoplasm.

Question 31

Explain how protein synthesis occurs?

Answer 31

1. DNA strands separate at one gene. mRNA strand copied from template strand of DNA. (This strand is known as the antisense strand, the sense strand has the same base sequence as the mRNA)
2. Process is catalysed by RNA polymerase enzyme.
3. mRNA moves out of the nucleus and into the cytoplasm, and becomes attached to a ribosome.
4. Molecules of tRNA carry individual amino acids to the surface of the ribosome.
5. tRNA anticodon lines up alongside a complementary codon, in the mRNA, held in place by hydrogen bonds, while enzymes link the amino acids together.
6. tRNA breaks away, and returns to the cytoplasm to pick up another amino acid.
7. The ribosomes move along the molecule of mRNA until it reaches the end, leaving a completed polypeptide chain.

The events in the nucleus involve the transcription of the DNA message. In the cytoplasm the message is Translated into polypeptide molecules and hence into proteins.

Question 32

What is the nature of the genetic code?

Answer 32

Triplets code for amino acids. A sequence of three bases is known as a codon. Some codons code for particular amino acids. Others code for the beginning or end of an amino acid sequence. (Start and stop codons.) The code is degenerate, many codons code for the same amino acid. Hence a mutation may not change the protein. The code is not overlapping.(although this is less economical it is also less limiting)

Question 33

what are mutations?

Answer 33

This is a permanent change in the DNA structure, arrangement or chromosome number of a cell.

Gene point mutation: error in DNA copying before cell division. substitution, deletion, insertion, inversion of bases.
e.g sickle cell anaemia: deficiency of healthy red blood cells.
there is a single base substitution: CTC -> CAC. this means that instead of Glutamic Acid being form Valine is formed. This alters the tertiary protein structure of beta haemoglobin.
This means less oxygen can be transported around that body. But causes resistance to malaria.

Chromosome mutations: this involves changes in the positions of genes within the chromosomes. Or an entire chromosome is lost or duplicated. e.g down’s syndrome is caused by 3 copies of chromosome 21.

Question 34

What are enzymes?

Answer 34

Enzymes are globular proteins that act as biological catalysts of chemical reactions. Catalysts alter the rate of chemical reactions without being changed or used up themselves.
Substrate + enzyme <=> enzyme substrate complex <=> enzyme + products

Enzymes catalyse a wide range of intracellular reactions as well as extracellular ones.

Question 35

What are the enzyme theories?

Answer 35

Lock and key theory: substrates ‘fit’ into the enzyme’s active site. This explains specify in which the specific characteristics of an enzyme means that each enzyme will only catalyse a specific reaction.

Induced fit theory: The active site is not completely rigid. Conformational change in enzyme she to better fit the substrate. Stresses bonds within the substrate -> lowering activation energy. Explains how an enzyme can catalyse a few different substrates.

Question 36

Factors affecting enzyme activity?

Answer 36

Temperature: More kinetic energy -> more successful collisions. Denature at extreme temps as images tertiary structure as peptide bonds break.

PH: Active site changes shape as PH changes.

Substrate concentration: more particels per cm3

Enzyme concentration: more particles per cm3

Question 37

How do you measure the reaction rate in an enzyme experiment?

Answer 37

to investigate the way a factor affects the rate of reaction, measure the initial rate of reaction each time the independent variable is changed. The initial rate of reaction is when the reaction proceeds at its fastest rate because there are no limiting factors. This gives the maximum reaction rate for an enzyme.

Question 38

What is reversible inhibition of enzymes?

Answer 38

When an inhibitor affects an enzyme in a way that does not permanently damage it, this is reversible inhibition. Reversible inhibition is a common feature of metabolic pathways, and it provides a key way of controlling reactions.

Competitive Inhibition:
These have a similar molecular shape to the substrate. And hence are able to occupy the active site, preventing the substrate from binding. It competes with the substrates to bind with active site.

Non-competitive inhibition:
These bind to the enzyme at a site which is NOT the active site. (allosteric site) The attachment causes a conformational change in shape of enzyme molecule, meaning that the active site can no longer accommodate the substrate. It is non-competitive as not competing for the same site.

Question 39

What is irreversible inhibition of enzymes?

Answer 39

In irreversible inhibition the inhibitor combines with the enzyme by permanent covalent bonding to one of the groups vital for cattily to occur. It changes the shape and structure of the molecule in such a way that it cannot be reversed. E.g cyanide

End-product inhibition:
this is a form of negative feedback. The product of a metabolic cycle or chain can regulate the rate of its own production by inhibiting an earlier enzyme in the metabolic pathway.

Question 40

What is the role of nitrate in plants?

Answer 40

to make DNA and amino acids

Question 41

What is the role of magnesium in plants?

Answer 41

to produce chlorophyll

Question 42

What is the role of calcium in plants?

Answer 42

to form calcium pectate for the middle lamellae

Question 43

What is the role of phosphate in plants?

Answer 43

to make ADP and ATP

Question 44

What are the properties and hence functions of water?

Answer 44

High specific heat capacity: it is slow to absorb and release heat as the hydrogen bonds between the molecules need lots of energy to break them. This helps living animals maintain a constant body temperature (due to the high water content of cells in which water acts as a buffer) maximising enzyme efficiency and metabolism.

Polar Solvent: it has both positively and negatively charged areas. This means water molecules are attracted to each other and hydrogen bonds form between hydrogen and oxygen of two molecules. This makes water very stable and it remains liquid over large range of temperatures. H2p can be used in metabolic reactions world wide and prevents aquatic animals freezing.
Also: because H2O is a polar solvent it is good at dissolving ionic substances due to attraction of opposite charges between molecules and ions. Important as all essential substances e.g glucose can be transported in a solution. most chemical reactions occur in water in cells.

maximum density at 4C: as it cools further the molecules become more widely spaced. hence ice is less dense than water and so floats. This forms an insulating layer preventing water beneath freezing so aquatic animals can still live in very cold places.

cohesion ( h+ bonds stick water molecules together) and adhesion (H2O sticks to other substances): Therefore water used in transport by plants in transpiration stream to supply mineral ions through xylem from roots to leaves and to give H2O to leaf cells for photosynthesis.

incompressibility: water is liquid so can not be compressed. important in hydraulic mechanism in organisms.

Surface tension: because of attraction between water molecules is greater that attraction between water and air. This forms a ‘skin’ so small animals can skate across ponds etc.