B2 Biology

B2 Biology- Edexel course

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  • Created by: charlotte
  • Created on: 01-06-11 11:26

DNA and Chromosomes

In normal human cells there are 23 pairs of chromosomes.

Chromosomes consist of long, coiled molecules of DNA (deoxyribonucleic acid)

Genes have codes for a particular inherited characteristis such as attached/unattached earlobes.

A DNA molecule consists o two strands, which are coiled to form a double helix. The strands are linked by a series of paired basis :

Adenine-Thymine (A-T)

Cytosine-Guanine (C-G)

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How DNA works

DNA contains the instructions for how the cells will join amino acids together in order to make specific proteins.

The instructions are in the form of a code and the order they are in should assemble amino acids to make protein.

There are about 20 amino acids in total which can be arranged in different orders and combinations to produce different proteins.

Proteins are molecules that the body requires to make hormones, skin and hair etc.. and also for growth and repair.

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Making Proteins

Organelles are specialised structures found in the cytoplasm of cells. Organelles called ribosomes are involved in protein synthesis.

The information needed to make the protein is stored in the DNA gene. The bases in DNA occur as triplets (eg ACG or ACC)

Each triplet codes for a single amino acid in a protein.

This code is stored in the coding strand of DNA and is copied to produce a molecule of messanger RNA (mRNA) This is called TRANSCRIPTION.

RNA is similar to DNA but unlike DNA it only has one strand and it can move outside the nucleus of the cell into the cytoplasm.

The RNA contains the code for linking the amino acids; the ribosomes interpret this code to link the acids to form a polypeptide (protein). This process is called TRANSLATION .

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Genetic Engineering

Sections of DNA that code for a specific protien can be transferred into microorganisms.

The microorganisms reprodue and make large quantities of the protein.

This is used for bacteria to produce large quantities ps the hormone insulin.

Fermentation-is the process by which microorganisms take food from their environment as an energy source and excrete waste substances like carbon dioxide, changing the substances in the surrounding medium over time.

A fermenter is a controlled environment -providing ideal conditions for the microorgainisms to produce the proteins they need.

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... is a large vessel used to cultivate microorganisms...it requires;

  • aseptic conditions (cannot be contaminated)
  • nutrients-(so they can grow)
  • an optimum temperature (to produce rapid growth)
  • correct pH level
  • oxyegnation- (need oxygen so they can respire)
  • agiatation (stirring) maintain an even temperature

microorgnisms are used in some food production

eg bread, beer and wine- yeast is used and yoghurt- bacteria is used

Yeast- is a single celled microorgansim. when oxygen is present it converts glucose to water and carbon dioxide. in the absence of oxygen it converts glucose to ethanol and carbon dioxide- this is called fermentation.

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Aerobic Resperation...

  • Energy is produced
  • Blood transports oxygen and food in the form of glucose
  • special enzymes in the cells cause the glucose and oxygen to react and energy is released.

Diffusion- glucose, oxygen and carbon dioxide move between the capillaries and respiring cells.

Ventilation-provides the oxygen needed for aerobic respiration

Glucose + oxygen -> carbon dioxide + water + energy

when exercising you heart rate increases so more oxygen can enter the body and more carbon dioxide removed

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Anaerobic Respiration...

  • during vigorous exercise the lungs and bloodstream cant always deliver enough oxygen to the muscle cells to respire the avaliable glucose and meet energy requirements.
  • the glucose can only be partly broken down (anerobic respiration)
  • anerobic respiration produces only a little bit of energy very quickly- and most of the glucose is changed to lactic acid - a waste product

oxygen debt- the build up of lactic acid cauing the muscles to stop contracting efficently

Amino Acids- a building block of a protein- they link up to form proteins

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Natasha Naeem


Helpful thanks. :-)



Thats ok :) i need to finish them !

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