Translation

This is the process that converts mRNA into functional proteins.

1. The mRNA molecule moves into the cytoplasm and attaches itself to a ribosome at its' 'start' codon.
2. The ribosome moves along the mRNA strand, 3 bases at a time.
3. As this happens, tRNA molecules base pair with the mRNA strand. These carry with them amino acids.
4. Adjacent amino acids will then bond, forming a protein.
5. The remaining tRNA and mRNA molecules will then split

Terms and Definitions

• Degenerative Code - This means that some amino acids are coded for by more than one codon
• Non-overlapping - Specific 'start' codons ensure that ribosomes 'read' the mRNA in the correct way.
• Introns - Reigons of non-coding DNA, removed from mRNA before translation
• Semi-conservative replication - When only half/one strand of the DNA is replicated. This produces exact copies of the origional DNA.
• Gene - A length of DNA that codes for a single protein.

Introns and Exons

Intron - Reigons of non-coding DNA. They are copied onto the nRNA during transcription then removed before they are used to code for proteins in the ribosome.

Exon - The coding reigon of DNA.

Transcription

This is the process that produces a molecule of mRNA from DNA.

1. The DNA helix unwinds as the hydrogen bonds between the base pairs break.
2. Free DNA nucleotides in the nucleus, pair with the exposed DNA bases on the sense strand.
3. These are held together using the enzyme DNA polymerase
4. This new strand of DNA nucleotides (mRNA) then separates from the sense strand and leaves the nucleus.

Bits Involved in Protein Synthesis

• DNA - Carried the code for all the proteins that a cell can make.
• mRNA - Messenger RNA copies the code for a single protein from DNA (transcription) and transports it to the ribosome in the cell's cytospasm.
• Ribosome - 'Reads' the mRNA code and assembles amino acids in their correct sequence to make a functional protein. This is called translation
• tRNA - Transfer RNA brings individual amino acids to the ribosome from the cytoplasm.

Methods of Enzyme Production

Fermentation

• The fermenter is filled with a sterile nutrient solution
• A fresh batch of a bacterium or fungus is then added to the fermenter.
• The paddles rotate to ensure the mixture is evenly spead
• As nutrients are used up, more are added. This is controlled by probes which detect the internal conditions
• The water jacket keeps the temperature down in the fermenter as it increases due to respiration of the microorganisms
• Air/Carbon dioxide is removed from the fermenter via an exhaust pipe.

Downstreaming Process

The stages carried out to isolate and purify an enzyme produced in a fermenter.

1. Growth of a large number of microorganisms
2. If enzymes are intracellular, they must be broken up first.
3. Enzymes are separated from incact cells, debris and other particles
4. Dilute impure solution os the enzyme (water is removed)
5. Concentrated, impure solution of the enzyme (impurities removed)
6. Concentrated purified solution or enzyme
7. Packaged
8. Distributed
9. Sold

Cereals and Crop Plants

A crop plant is one that humans grow for a specific purpose. Cereals are crops that are grown for their grain. They include:

Rice -Maize - Sorghum

Each are grown in different conditions and have specific requirements.


Rice

• CONDITIONS: warm swamps.
• PROBLEM: waterlogged soil with low oxygen concentration.
• SOLUTIONS:

1. Rice respires anaerobically producing ethanol. Plant tissue is tollerant of high concentrations.
2. Stems contain aerenchyma. These allow oxygen diffusion to the roots, enabling aerobic respiration. They also provide buoyancy keeping photosynthesising leaves near the light.

Maize

• CONDITIONS: Hot
• PROBLEM: Stomatas close preventing water loss, BUT CO2 cannot enter the plant
• SOLUTIONS:

1. C4 Pathway allows plant to take in CO2 at low concentrations, and photosynthesise using a 4-C compound. This uses lots of ATP and so occurs in high light intensities.

SORGHUM-A Xerophyte

• CONDITION: Hot and Dry
• PROBLEM: Water Loss
• SOLUTIONS: increase water uptake and reduce water loss.

1. Extensive root system enables uptake over a large area of soil
2. Thick waxy cuticle on upper surface of leaf reduced water evaporation
3. Very few stomata in the leaf
4. Leaves roll inwards in dry conditions to trapping a layer of moist air
5. Tollerant of high temperatures

Aseptic Conditions

Aseptic conditions are required to ensure that no baceria microorganisms enter the fermenter. If they did, it could cause the entire culture to be destroyed. The fermenter, and process is therfore adjusted to ensure they cannot enter the system:

• Washing: Removed the majority of the culture medium
• Disinfecting: Kills microorganisms
• Steam Cleaning: The heat kils the microorganisms and gets into all parts of the fermenter.

Specific parts are also designed to keep microorganisms and bacteria out:

• Inlet and outlet pipes all have filters
• All joints are sealed
• The surfaces of the fermenter are smooth and polished so that there are no rough surfaces for microorganisms to enter and hide in.

Finally, the culture medium is also sterilised to ensure there are no live microorganisms in it before it is put into the fermenter.

Immobilised enzymes

An immobilised enzyme is one that is bound immovably to a surface rather than being dissolved in solution. They offer certain advantages and disadvantages.

Advantages

• Reactions can be run continually
• They can be recovered and used over and over again which is particularly useful when an enzyme is difficult or expensive to produce
• Products won't be contaminated by the enzymes
• The matrix makes the enzymes more stable so that they can be used over a wider range of temperatures and pH's

Disadvantages

• Immobilisation can affect the shape and properties of the enzymes so the substrate may not bind as effectively. This causes a reduced rate of reaction.
• This disadvantge may be offset however by the increase in temperature, or the ability to run the reaction continuously.