Sl The Chemistry Of Life

Front 1

State that the most frequently occurring chemical elements in living things are carbon, hydrogen, oxygen and nitrogen

Back 1

The most frequently occurring chemical elements in living things are carbon, hydrogen, oxygen and nitrogen.

Front 2

State that a variety of other elements are needed by living organisms, including sulfur, calcium, phosphorus, iron and sodium

Back 2

A variety of other elements are needed by living organisms, including sulphur, calcium, phosphorous, iron and sodium.

Front 3

State one role for sulfur, calcium, phosphorus, iron and sodium

Back 3

Sulfur: Prokaryotes - proteins, lants - proteins, Animals - proteins
Calcium: Prokaryotes - flagella movement, Plants - forms plate during cytokinesis, Animals - Shells, bones and teeth
Phosphorus: Prokaryotes - Nucleic acids and ATP, Plants - Nucleic acids and ATP, Animals - Nucleic acids and ATP
Iron: Prokaryotes - cytochrome (used in respiration), Plants - cytochromes (used in mitochondrial respiration), Animals - cytochromes (used in mitochondrial respiration) and Haemoglobin
Sodium: Plants - cation in cytoplasm, Animals - transmission in nerve impulses

Front 4

Draw and label a diagram showing the structure of water molecules to show their polarity and hydrogen bond formation

Back 4

.

Front 5

Outline the thermal, cohesive and solvent properties of water

Back 5

Thermal - Water requires a high input of energy to break the hydrogen bonds and turn it from the liquid state to the vapour state, evaporation of water off the surface of an organisms allows it to lose heat.
Cohesive - Hydrogen bonds link water molecules together
Solvent - Water is a good solvent due to its polarity

Front 6

Distinguish between organic and inorganic compounds

Back 6

Compounds containing carbon that are found in living organisms (except hydrogencarbonates, carbonates and oxides of carbon) are regarded as organic.

Front 7

Explain the relationship between the properties of water and its uses in living organisms as a coolant, medium for metabolic reactions and transport medium

Back 7

Coolant (thermal property) - Mammals sweat for thermoregulation, plants in the desert increase transpiration when in danger of over-heating
.
Medium for metabolic reactions (solvent) - Metabolic reactions can take place easily between substances dissolved in a liquid medium.

Transport medium (cohesive) - As molecules evaporate from the surface of a leaf further water molecules are pulled from behind creating the transpiration stream in the xylem. Dissolved substances are transported in the transpiration stream.

Front 8

Identify amino acids from diagrams showing their structure

Back 8

.

Front 9

Identify glucose from a diagram showing its structure

Back 9

.

Front 10

Identify ribose from a diagram showing its structure

Back 10

.

Front 11

Identify fatty acids from diagrams showing their structure

Back 11

.

Front 12

List three examples each of monosaccharides, disaccharides and polysaccharides.

Back 12

Monosaccharides:glucose, galactose and fructose

Disaccharides: maltose (glucose + glucose), lactose (glucose + galactose) and sucrose (glucose + fructose)

Polysaccharides: starch, glycogen and cellulose

Front 13

State one function of glucose, lactose and glycogen in animals

Back 13

Glucose - Broken down in respiration to release energy

Lactose - Sugar in milk produced by mammals

Glycogen - Energy store in liver and skeletal muscles

Front 14

State one function of fructose, sucrose and cellulose in plants

Back 14

Fructose - Energy source and component of sucrose

Sucrose - Unreactive and so transported around the plant

Cellulose - Main component of the cell wall

Front 15

Outline the role of condensation and hydrolysis in the relationship between monosaccharides, disaccharides and polysaccharides

Back 15

.

Front 16

Outline the role of condensation and hydrolysis in the relationship between amino acids and polypeptides

Back 16

.

Front 17

Outline the role of condensation and hydrolysis in the relationship between fatty acids, glycerol and triglycerides

Back 17

.

Front 18

State three functions of lipids

Back 18

1. Energy storage in plants and animals
2. Thermal insulation in animals as sub-cutaneous fat
3. Main component of myelin sheath of neurons

Front 19

Compare the use of carbohydrates and lipids in energy storage

Back 19

Carbohydrates:
- 17KJ of energy released per gram
- Easily built up for storage
- Easily broken down to release energy quickly
- Glycogen in animals, starch in plants
- Both of these converted to glucose when energy is required

Lipids:
- 38KJ of energy released per gram
- Hence, much more efficient energy store
- Storage efficiency increased because lipids are hydrophobic and less mass is taken up by storing water
- Metabolic pathways to build up and break down more complex, and therefore slower
- Converted to fatty acids and glycerol when energy required
- Both of these converted to coA

Front 20

Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate

Back 20

.

Front 21

State the names of the four bases in DNA

Back 21

Adenine, Thymine, Cytosine and Guanine

Front 22

Outline how DNA nucleotides are linked together by covalent bonds into a single strand

Back 22

.

Front 23

Explain DNA replication

Back 23

1. The DNA double helix is unwound and separated into strands by breaking the hydrogen bonds. The main enzyme involved is helicase.
2. The single strands act as templates for new strands. Free nucleotides are present in large numbers around the replication fork. The bases of these free nucleotides form hydrogen bonds with the bases of the parent strand through complementary base pairing. The bases ae all linked together to form the new strand. DNA polymerase is the main enzyme involved.
3. The daughter DNA molecules each rewind into a double helix. The two daughter DNA molecules are identical in base sequence to each other, and the parent molecule because of complementary base pairing.

Front 24

Explain the significance of complementary base pairing in the conservation of the base sequence of DNA

Back 24

- DNA carries the genetic code
- This code is the linear sequence of bases
-Thus, this sequence must be preserved
-In the original sequence of DNA A is paired with T, and C is paired with G
- When the new strand is built on to the original, they remain with the same base pairs

Front 25

State that DNA replication is semiconservative

Back 25

DNA replication is semi-conservative.

Front 26

Compare the structure of RNA and DNA

Back 26

DNA: Feature: RNA
Deoxyribose: Sugar: Ribose
A, T, C, G: Bases: A, U, G, C
2: Number of Strands: 1

Front 27

Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase

Back 27

Note: Only one side of the DNA is copied, RNA nuclotides are used (there is a pool of these in the nucleoplasm), the enzyme is RNA polymerase.

1. DNA is unzipped by RNA polymerase.
2. RNA polymerase builds mRNA by base pairing mRNA nucleotides onto the strand of DNA opposite the gene.
3. Uracil (U) is used instead of Thymine (T).
4. mRNA is released and leaves the nucleus.

Front 28

Describe the genetic code in terms of codons composed of triplets of bases

Back 28

- A codon is composed of three mRNA bases
- Most codons codes for an amino acid
- There is a table of 64 codons, but only 61 code for amino acids. The remaining three are stop codons, they do not have an amino acid, and so mark the end of the 'message' on the mRNA.
- All but two amino acids have more than one codon. This is called degeneracy.
- All organisms use the same code, so it is called universal.

Front 29

Explain the process of translation, leading to polypeptide formation

Back 29

1. mRNA moves from the nucleus and attaches to ribosome in cytoplasm.
2. First tRNA with amino acid joins to first codon by base pairing codon and anticodon.
3. Second tRNA with amino acid joins to second codon by base pairing codon and anticodon.
4.The two amino acids are now alongside each other and a peptide bond forms between them.
5. Ribosomes shift along one mRNA triplet.
6. In comes the thirds tRNA and step 4 is repeated.
7. Steps 5 and 6 are now repeated until the stop codon is reached.
8. mRNA and ribosome spate and the completed polypeptide breaks free.

Note: Sequence of DNA nucleotides --> transcription --> sequence of mRNA nucleotides --> translation --> sequence of amino acids (polypeptide)

Front 30

Define enzyme and active site

Back 30

Enzyme: globular proteins used to catalyze chemical reactions.
Active site: The binding site on the surface of an enzyme where catalysis occurs.

Front 31

Explain enzyme–substrate specificity

Back 31

Enzymes fold to form a three dimensional globular structure. The folding creates a specifically shaped three-dimensional pocket on the surface into with the substrate or substrates can fit. The shape of an active site exactly matches the shape of the substrate(s). This brings substrates together in the correct orientation.

Front 32

Explain the effects of temperature on enzyme activity

Back 32

There is an approximately exponential increase up to the optimum temperature and then a sharp drop. As the temperature rises, reacting molecules have more kinetic energy. This increases the likelihood that a reaction rate will occur. Beyond the optimum temperature the amino acids within the protein are moving so much that the weak bonds are broken and the molecule begins to break down.

Front 33

Explain the effects of substrate concentration on enzyme activity

Back 33

As substrate concentration increases between A and B more collisions occur with enzyme and so more reactions occur. At point B, all the active sites are occupied by substrate at one time and so there can be no further increase in reaction rate.

Front 34

Explain the effects of pH on enzyme activity

Back 34

Enzymes are large protein molecules folded into a complex 3D shape. This is held in place by bonds, and these are strongest at the optimum pH. Changing the pH affects these bonds and so the shape of the molecule, and hence the active site, changes. If the substrate can no longer bind to the active site then the reaction rate drops.

Front 35

Define denaturation

Back 35

Denaturation is a structural change in a protein that results in the loss (usually permanent) of its biological properties. Refer only to heat and pH as agents.

Front 36

Explain the use of lactase in the production of lactose-free milk

Back 36

- Lactose is a disacchirade, which cannot at times be absorbed by the gut.
- Milk is treated with lactase, and this breaks down the lactose to the monosaccharides glucose and galactose which are easily absorbed by the gut.
- The lactase is often immobilised and the milk is passes over it. This prevents the lactase from being in the product, and is more economical, as the lactase can be used repeatedly.
- Lactase is obtained from the fungus kluyveromyces lactis (a yeast).
- Lactose-free milk is used in the production of ice cream, as the use of lactose makes it crystalise and become granular.
- In yoghurt and cheese production, bacteria ferment lactose slowly, but ferment glucose and galactose quickly, making production faster.
- Lactose-free products are sweeter than those containing lactose.

Front 37

Define cell respiration

Back 37

Cell respiration is the controlled release of energy from organic compounds in the form of ATP.

Front 38

State that, in cell respiration, glucose in the cytoplasm is broken down by
glycolysis into pyruvate, with a small yield of ATP

Back 38

In cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP

Front 39

Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP

Back 39

If no oxygen is available, the pyruvate remains in the cytoplasm and is converted into a waste product that can be removed from the cell. The waste product is lactate (lactic acid) in humans. In yeast and plants the waste products are carbon dioxide and ethanol. There is no further yield of ATP.

Front 40

Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP

Back 40

In aerobic cell respiration, oxygen is present in abundance. Pyruvate can be broken down further in mitochondria into carbon dioxide and water, with a large yield of ATP.
C6H12O6 + 6O2 --> 6CO2 + 6H2O + ATP

Front 41

State that photosynthesis involves the conversion of light energy into chemical energy

Back 41

Photosynthesis involves the conversion of light energy into chemical energy.

Front 42

State that light from the Sun is composed of a range of wavelengths (colours)

Back 42

Light from the Sun is composed of a range of wavelengths (colours).

Front 43

State that chlorophyll is the main photosynthetic pigment

Back 43

Chlorophyll is the main photosynthetic pigment.

Front 44

Outline the differences in absorption of red, blue and green light by chlorophyll

Back 44

Chlorophyll can absorb some colours or wavelengths of light better than others. It absorbs most at the red and blue ends of the spectrum. The green light that cannot be absorbed is reflected. This makes chlorophyll, chloroplasts and plant leaves green, as we see this green reflected light.

Front 45

State that light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen

Back 45

Light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen.

Front 46

State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules

Back 46

ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.

Front 47

Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass

Back 47

Production of oxygen: volume of oxygen released by photosynthesis can be measured using a small measuring cylinder or syringe.
Uptake of CO2: As carbon dioxide is taken out of the solution the pH increases. This can be measured be a pH probe.
Increase in biomass: Equal sized samples are taken at specific time intervals and percentage increase in the dry mass measured the rate of photosynthesis can be determined.

Front 48

Outline the effects of temperature on the rate of photosynthesis

Back 48

Many of the reactions of photosynthesis are enzyme controlled and hence the rate of photosynthesis shows the same shape as the graph representing temperature’s effect on enzymes.

Front 49

Outline the effects of light intensity on the rate of photosynthesis

Back 49

As the intensity increases, there comes a point when all the chlorophyll molecules are saturated and cannot accept any more light. A minimum intensity is required before photosynthesis starts.

Front 50

Outline the effects of carbon dioxide concentration on the rate of photosynthesis

Back 50

This is a substrate for an enzyme controlled reaction, and once all the enzyme active sites are used up the reaction cannot go any faster. A minimum concentration of carbon dioxide is required before photosynthesis starts.