Gcse B3 OCR gateway biology

Gcse B3 OCR gateway biology - Enzymes and stuff

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  • Created by: Jess
  • Created on: 23-02-12 22:21


Respiration occurs in every cell in our body (mitochondria)

It's the process of releasing energy from within glucose.

This energy cannot be used directly, so it is used to make a substance called ATP.

ATP acts as the energy source for many cell processes and transports energy to where it's needed.

Respiration is controlled by enzymes, this means the rate of respiration is affected by pH and temp.

Here are two types; anaerobic and aerobic.

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Aerobic respiration

Aerobic = with oxygen

This occurs when there's plenty of oxygen.

It's the most efficient way of releasing energy from glucose.

This respiration is used most of the time.


Glucose + oxygen -> cardon dioxide + water + energy

C(6)H(12)O(6) + 6O(2) -> 6CO(2) + 6H(2)O + energy.

Respiration rate increase = increase in oxygen comsumption and carbon dioxide production

Rate of oxygen consumption cann allow for an estimate of the metabolic rate (amount of energy being used)

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Anaerobic Respiraton

Anaerobic = without oxygen

When you do vigorous exercise, your body cannot supply the muscles with enough oxygen for aerobic respiration.

Your heart rate and breathing rate increase, but you still have to begin anaerobic respiration.

It releases less energy per glucose molecule. In anaerobic respiration, the glucose is only partially broken down. Lactic acid is also produced, this then builds up in your muscles and causes muscle fatigue and can become painful.

Equation = glucose -> lactic acid + energy

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Anaerobic pt II

Advantage to anaerobic is that you still get to use your muscles.

After resorting to anaerobic, you'll have an oxygen debt after the exercising.

You need extra oxygen in order to break down the lactic acid that has built up and to allow aerobic respiration to happen again.

This means your breathing rate is still increased for a while after exercising, so you can repay the oxygen debt.

Your heart rate will stay high also because the lactic acid has to be transported to the liver to be broken down.

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The respiratory quotient

The respiratory quotient tells you whether someone is respiring aerobically or anaerobically.

RQ = Amount of carbon dioxide produced / amount of oxygen used

The RQ Is usually between 0.7 and 1 ( aerobic)
If RQ is above 1.0 then the person is short of breath and is repairing anaerobically as well.

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Animal Cell

Nucleus - Contains DNA in the form of chromosomes.

Cell membrane - holds cell together and controls what goes in and out

Ribosome- where proteins get synthesised

Cytoplasm - where most chemical reactions take place

Mitochondria - where most of the reactions involved in respiration take pleace. Cells that need lots of energy contain many mitochondria...

Liver cells - needed for metabolic reactions

Muscle Cells - need energy to contract

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Plant Cell

Nucleus - Contains DNA in the form of chromosomes.

Cell membrane - holds cell together and controls what goes in and out

Cytoplasm - where most chemical reactions take place.

Chloroplasts - where photosynthesis happens

Vacuole - a large starcture containing cell sap (sugar and salt solution)

Cell wall - made of cellulose. It supports the cell. 

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Bacteria Cell

Cytoplasm - where most chemical reactions take place.

Cell membrane - holds cell together and controls what goes in and out

Cell wall - made of cellulose. It supports the cell.

Singular circular starnd of DNA - floats freely in cytoplasm

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Chromosomes are long molecules of coiled DNA.

DNA is divided into short sections - genes

DNA = a double helix shape made up of small groups called nucleotides

Nucleotides contain bases

Bases = A,C,T,G

A+T = complimentary base pairing

C+G = complimentary base pairing

each base forms cross links to the other strand where it joins with it complimentary base pair - this keeps the DNA tightly wound.

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Watson and Crick

first scientists to build a model of DNA in 1953

They used data from other scientists

X-ray data showing the two strands and double helix

Other data showing bases were in pairs.

By putting this data together they could build the model of DNA

This wasnt accepted at first, but more research has confirmed this by making sure reliable results were used.

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DNA replication

DNA copies itself every time a cell divides.

The DNA 'unzips' itself to form two single strands.

New nucleotides join on using complimentary base pairing. This makes an exact copy on the DNA on the other strand.

The reulst is two double stranded DNA molecules that are identical.

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DNA contrains the protein production in a cell by controlling protein synthesis.

A section of DNA that codes for a particular protein is called a gene

Proteins = chains of molecules called amino acids.

Unique protein = unique number and order of amino acids

This gives each protein a different shape giving it a different function.

The order of bases in a gene decides the order of amino acids in a protein

One amino acid is coded for by three bases

The amino acids are joined together to make the protein, following the order of the bases in a gene.

Different sequence = unique protein.

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proteins are mad ein the cell cytoplasm by ribosomes.

to make a protein: Ribosomes use the code in DNA but DNA cannot exit the nucleus because its too big. The cell needs to get the code from DNA -> ribosome

This is done by using a molecule called mRNA - which is made by copying the code from DNA.

The mRNA acts as a messenger between the DNA and the ribosome as it carries the code between the two

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DNA controlling the cell

The proteins produced in a cell affect how it functions.

Some of them determine cell structure or cell reactions.

Different types of cell = different functions because the make different proteins

They only make certain proteins because only some of the full set of genes is used in any one cell.

Some genes are 'switched off' which means the proteins they code for arent produced.

The genes that are switched on determines the function of the cell...

Muscle cell = muscle cell proteins are switched on, nerve/ skin celll proteins are switched off, allowing it to function.

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Functions of proteins

Carrier Molecules - used to tarnsport smaller molecules e.g. Haemoglobin transporting oxygen

Enzymes - control cell reactions

Structural proteins - physically strong e.g. collagen strengthens connective tissues.

Hormones- carry messages around the body e.g insulin released pancreas to regulate blood sugar levels.

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Enzymes & Cell reactions

Cells have lots of chemical recations going on, like photosynthesis, protein synthesis and respiration.

These reactions must be controlled to allow the right amount of substance to be produced

Raising the temp can often speed up reactions but there is an optimum.

Living things produce enzymes which act as biological catalysts. A catalyst speeds up a reaction without being changed or used up itself.

We only have enzymes to speed up useful chemical reactions and reduce the need for heat.

Every biological reaction has its own ezyme.

Each enzyme is coded for by a gene and has a unique shape.

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Enzyme specifity

Chemical reactions involed; things being split apart or joined together.

substrate = thing changed in the reaction.

Every enzyme has an active site, this is where the substrate joins and the reaction is catalysed.

Enzymes are highly specific and usually only fit with one substrate. This is known as being highly specific for their substrate.

The substrate must fit the active site. If it doesnt fit the recation wont be catalysed.

THis is called the lock and key mechanism.

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Optimum Temperature

Changing the temp can change the rate of reaction.

more heat -> more energy -> higher collision rate

less heat -> less energy -> lower collision rate

Is its too hot, some of the bond sin the enzyme can be broken. The enzyme can lose its shape and its active site shape, so it can no longer catalyse a reaction.

This is denaturing and its an irreversible reaction.

Each enzyme has its own optimum temperature, when the reaction is at its fastest.

Most human enzymes function best at 37 degrees celsius.

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Enzymes & pH

If pH is too high, or too low, It interferes with the bonds.

This can also change the shape of the enzyme and can lead to denaturing

All enzymes have an optimum pH, its often pH 7 (neutral)

But some enzymes are used to break down proteins in the stomach (pepsin) and it works best at pH 2 so it functions best in acidic conditions.

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The Q(10) Value

The Q(10) value for a reaction shows how much the rate changes when the temperature is raised by 10 degrees celsius.

Q(10) = Rate at higher temperature / Rate at lower temperature

If the Q(10) is 2, then the reaction doubles, if its 3, the reaction rate has trebled.

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Gene Mutations

A gene mutation is a change in the DNA base sequence.

 If this occurs within a gene, it can stop the production of a protein or produce a different one.

Producing the wrong or no protein can seriously affect your health.

If a mutation occurs in a reproductive cell, the offspring might develop abornamlly or die.

If a mutation occurs in body cells, the mutant cells can often divide uncontrollably and spread to other parts of the body, this is cancer.

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Beneficial and other Mutations

Sometimes the mutations can actually be of benefit to an organism.

This can give the organism a survival advantage, this can then pass on to the offspring and spread its way through the population.

This is what evoution and natural selection is based around.

Ths is what can happen to bacterium strands that become resistant to antibiotics, the mutant gene lives and creates a resistant strain of the baceria.

Soem mutations have no effect on the protein being coded for so they have no effetc on the organism.

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Radiation and chemical effects on DNA

Mutations can occur spontaneously when the the chromosome doesn tcopy itself properly, these chances can increase if you're exposed too;

IONISING RADIATION: x-rays, ultraviolet lights together with the radiation from the radioactice substances. The gerater the dosage of radiation, the greater the risk of mutation.

CHEMICALS: cigarette smoke, this contains mutagens or carcinogens. These can cause mutations.

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Being multicellular

Advantages: being multicellular can make you bigger, travel further and get nutrients in a variety of ways. Fewer threats, e.g. eaten, killed.

Cell differentiation - different cells do different jobs, so they can be specialists in what they do.

Multicellualr = More complex. Specialised organs, different shapes, different behaviour, special adaptations to their environment.

But, being multicellular means you have to have specialised organ systems, such as;

- Communication system between different cells, e.g. nervous system.

- A supply system to give the cells the nutrients they need e.g. circulatory system

- A system that controls the exchange in substances with the environment e.g. respiratory system

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Mitosis is when a cell reproduces itself by splitting to form two identical offspring.

Mitosis is used for growth and repair, the offspring can be used to replace old cells

1) Before mitosis starts, the DNA in the cell is replicated.

2)Then at the beginning of mitosis, the DNA coils into double-armed chromosomes. These are exact copies of eachother.

3)The chromosomes line up at the centre of the cell and then divide as cell fibres pull them apart. The two arms of each chromosomes go to opposite poles of one cell. Membranes form around each of these two different sets of chromosomes.

4)The cytoplasm divides and gets two new cells containing the exact same genetic material

5) You've ended up with two new cells that are genetically identical, Before these divide again, the DNA has to replcate itself to give each chromosome two arms.

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brilliant - just what i needed. thank you!!! 


Thank you! very helpful!!!


thank you so much, this really helped with my revision!


Very helpful! Thank you :)


This helped me a lot, thank you!! :-)

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