Biology Unit 3 Chemistry of Life Bite Size

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Properties of Water

Water molecules are polar

Oxygen atoms (negative charge) are attracted to hydrogen atoms = HYDROGEN BOND

Thermal Properties - heat capacity, high boiling and freezing points, cooling effect of evaporation

Water has a large heat capacity - needs a considerable amount of energy to increase temperature. Hydrogen bonds strength is not easily broken. TEMPERATURE OF WATER TENDS TO REMAIN STABLE - good for animals that use water as a habitat. 


Cohesion Properties - Hydrogen bonds hold water molecules together, water moves up plants because of cohesion. Long columns of water can be sucked up from roots to leaves without columns breaking


Solvent Properties - different substances can dissolve in it because of the polarity

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Role of condensation and hydrolysis in carbohydrat

When 2 monosaccharides combine they form a disaccharide and water. 

This is called a CONDENSATION REACTION. It produces water

The reverse of this is called HYDROLYSIS

Glucose + glucose = maltose + water

Glucose + fructose = sucrose + water

Glucose + galactose = lactose + water

Adding more monosaccharides will produce polysaccharides 

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Role of condensation and hydrolysis in Lipids

Lipids are made with glycerol and 1, 2 or 3 Fatty acids

Triglycerides = glycerol and 3 datty acids formed by a CONDENSATION REACTION of glycerol and 3 fatty acids. 

Glycerol + 3 fatty acids = triglyceride + 3 water 

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Role of condensation and hydrolysis in proteins

Two amino acids can combine to form a DIPEPTIDE 

This is a special bond called a Peptide Bond 

Amino Acid 1 + Amino acid 2 = dipeptide + water 

As more amino acids are added they produce a polypeptide and more water

A polypeptide can be a protein  by itself, or combine with another one to be a protein

Example: Hemoglobin - 4 polypeptide chains: 2 alpha and 2 beta

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The Structure of the DNA nucleotide

DNA is found in the nucleus (deoxyribonucleic acid)

RNA is found in the cytoplasm. (ribonucleic acid) 

DNA sugar - deoxyribose

RNA sugar - ribose 

Nucleic acids - long chain molecules (similar to proteins) building blocks are called nucleotides.

Nucleotides - Sugar, phosphate PO4-3 group, organic base (nitrogenous base) 

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DNA nucleotides - covalent bond linkage

DNA is composed of two polynucleotide chains

Phosphate + sugar + organic base = nucleotide + 2 water

This is a condensation reaction.

The chains are formed through Covalent Bonds between the phosphate of one nucleotide to the sugar of the next nucleotide. 

This forms a "backbone" made up of phosphate and (deoxy)ribose and an organic base attached to every ribose. 


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Significance of comp. base pairing

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

Every organic base can only fit with one other one. (complementary base pairing) 

The "new" strand of DNA that is coded off of the "old" strand is identical (during DNA replication

In theory: the process could continue forever without any change to genetic material. 

Sometimes mistakes occur, and these are called mutations.

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DNA transcription (protein synthesis part 1)

Transcription - similar to DNA replication. 

Takes place in the nucleus, and involves a section of DNA that needs to "unzip". 

Only ONE of the two strands of DNA is transcribed. (The anti-sense strand) 

From the anti-sense strand, a complementary RNA strand is made. 

This is called messenger RNA (mRNA)

It has the same sequence of nucleotides (as the "sense" strand) except for uracil instead of thymine binding to adenine. 

After transcription, mRNA leaves nucleus, and goes into cytoplasm. 

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The genetic code

Genetic code - based on sets of 3 nucleotides called codons.

There are 20 amino acids commonly found in cells. 

Not possible to have 4 different nucleotides to code for all of them. 

If you use 2 sets of nucleotides 4 x 4 = 16  This is still not enough as it is only 16 different combinations and we need 20. 

The next best solution is 3 nucleotides 4 x 4 x 4 = 64. 

This is more than the required 20, but it means that more than one codon can code for a single amino acid. 

They can also have codons that are "stop" and "start" codons. 

The sequence of the codons in the mRNA determinws the sequence of the amino acids in the polypeptide

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One gene, one polypeptide relationship

"one gene - one polypeptide" concept - EVERY POLYPEPTIDE CHAIN IS CODED FOR BY ONE GENE. 

ie. a gene can only code for one polypeptide chain. 

Example: Hemoglobin (4 chains - 2 alpha, 2 beta) to code for this, you need 2 genes. 

This theory, like so many in biology has exceptions. e.g.

1) Some genes code for types of RNA which do not produce polypeptides.

2) Some genes control the expression of other genes.

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Anaerobic cell respiration

Oxidation of organic compounds without oxygen (less efficient than aerobic respiration) 

glycolysis is carried out first, to continue pyruvate needs to be changed into another substance. 

Human: Used when we run a sprint, as we suddenly require a lot of energy. 

location: cytoplasm

Substrate: glucose

Product: lactate + ATP

Yeast: used in breadmaking so dough will rise. CO2 creates bubbles (this is the rise) 

location: cytoplasm

Substrate: glucose

Product: ethanol + CO2 + ATP

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Aerobic cell respiration

If oxygen is present -> pyruvate produced in cytoplasm during glycolysis will move to the mitochondria. 

Pyruvate will be broken down into CO2 + water and a lot of ATP. 

(a lot more than glycolysis and anaerobic respiration)

1. Glucose in cell (initial substrate for respiration

2. Glycolysis occurs - breaks down into pyruvate

3. Pyruvate is broken down and oxidised further in the mitochondria where alot of ATP is produced. 

4.  Oxygen is required for (3) to occur. It is transported by haemoglobin found in red blood cells. 

5. CO2 is a waste product from aerobic respiration, diffuses into blood -> lungs -> exhaled

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Absorption of light

The main colour of light absorbed by chlorophyll is red and blue

The main colour reflected (not absorbed) is green.

Hence why so many plants are seen as green, the light is reflected from the chlorophyll to your eye

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Effects of variables on rate of photosynthesis

Photosynthesis needs: chlorophyll, light, carbon dioxide, water, good temperature. 


biological reactions require enzymes. Enzymes have "optimal" temperatures for most effectiveness. 

Rate of photosynthesis increase as temperature rises to "optimal" level

Decreases when enzymes denature because of too high temperature. 

CO2 Concentration: 

CO2 is a reactant, as concentration increases rate of reaction increases. Once it reaches "maximum" level, photosynthesis rate stays the same. 

Light intensity: 

at very low levels, plant is respiring not photosynthesising, as the light intensity increase, rate increases, and stays the same at maximum level. 

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