Page 2
WE SHALL LOOK AT PROTEIN SYNTHESIS.
CONSIDER PROTEIN STRUCTURE AT THE MOLECULAR LEVEL.
DISCUSS DIFERENT USES OF PROTEINS.
BREIFLY LOOK AT ENZYMES.
Page 3
Protein synthesis
Protein synthesis is the making of proteins, using the information that is found in DNA (Chromosomes).
chro CELL
Page 4
Proteins
Proteins are very important molecules for a cell.
Proteins are used to build cell structures and are used as enzymes.
Chromos omes
The cell Nucleus
Proteins
Proteins are long chains of small molecules called amino acids.
Different proteins are made using different sequences of amino acids.
The pieces of information in DNA are called genes.
Genes describe how to make proteins by putting the correct amino acids into a long chain in the correct order.
The cell
Piece of DNA Selected
For study
chromosomes Nucleus
Page 7
Nucleus
Piece of DNA Selected for
study
Let’s zoom in on This short segment of
DNA to see how its information
Is used.
Page 8
DNA inside the nucleus
Protein synthesis begins with the stored genetic information of a DNA molecule.
The DNA of this gene will ‘unzip’ like DNA does during replication.
D N A
Page 9
Unu
Page 10
d
D N A
D N RNA A
The new strand is an RNA molecule. Note that there is one difference in the subunits: RNA contains yellow Uricil instead of
purple Thymine. D
N
A RNA
D N A The RNA now has copied the subunit
sequence of the gene.
The DNA is no longer needed in the process of protein synthesis.
Page 13
D N A D
N
A RNA
Page 14
RNA
Page 15
mRNA At the ribosome A]
ion will rotein
At the ribosome
Page 16
At the ribosome
The genetic information is interpreted and used to assemble a protein.
We should remember, the mRNA is a sequence of subunits (like a chain) that tells how to build a protein
A protein is a sequence of subunits – a chain of amino acids.
The mRNA contains information in sets of three subunits.
Each set of three is the code for a particular amino acid.
m R N A
The information of the messenger RNA (mRNA) describes which amino acids should be in the
protein chain.
A molecule of transfer RNA (tRNA) will carry in the proper amino acid, one at a time.
Page 19
.
m R N A
Page 20
m R N A Amino acid
Page 21
Two different Amino acids
Two different tRNA molecules
A different set of three mRNA subunits means a different tRNA molecule. That means a different amino acid will be
Carried in.
m R N A
Page 22
The next tRNA will Carry in the proper
amino acid and the process will
continue.
The chain of amino acids is called a ‘polypeptide’
And when it is very long it is called a protein.
polypeptide
Page 25
A polypeptide chain
Even this is a very, very short polypeptide chain. Most have hundreds or thousands of amino acids.
A very short polypeptide chain, or part of a protein
Page 26
The end of protein synthesis at the ribosome.
Page 27
We will look at the main elements found in proteins.
Recall how proteins are constructed.
Look at the structure of proteins.
Overview the major functions of proteins.
PROTEIN STRUCTURE
Page 28
The building blocks of proteins
Like carbohydrate and lipid molecules proteins contain the elements : Oxygen(O), Carbon(C),and Hydrogen(H)
In addition they always contain the element Nitrogen(N).
Before we can understand how proteins are constructed, the structure of amino acids needs to be considered.
N C C H
H
R
H
O
OH
AN AMINO ACID Amine group
Carboxylic acid group R represents groups such as CH3 or C2H5
Page 31
How are proteins constructed
First the Amino acids bond together.
They are joined together by what is known as a peptide bond.
Page 32
Formation of a peptide bond via condensation.
H R O H R O
N C C + N C C
H H OH H H OH
Amino acid Amino acid
Page 33
A peptide bond between two amino acids.
H R O H H O N C C N C C H H R OH
H20 [WATER]
A condensation reaction Page 34
Protein construction
When two amino acids join together they form a dipeptide.
When many amino acids are joined together a long-chain polypeptide is formed.
Organisms join amino acids in different linear sequences to form a variety of polypeptides in to complex molecules, the proteins.
Primary protein structure Peptide bond
Amino acid
primary
structure
This is the linear sequence of amino acids
Secondary protein structure
Polypeptides become twisted or coiled.
These shapes are known as the secondary Structure.
There are two common secondary structures
The alpha-helix and the beta-pleated sheet.
Page 37
Amino acid
Hydrogen bonds hold shape together Secondary protein structure
Alpha-helix
Page 38
Secondary Protein structure [The beta pleated sheet]
Amino acid
Page 39
Hydrogen bonds
The polypeptides are held in position by hydrogen bonds.
In both alpha-helices and beta pleated sheets the C=O of one amino acid bonds to the
H-N of an adjacent amino acid.
As below:
C=O----H-N
Page 40
Secondary structures
Both secondary structures give additional strength to proteins. The alpha- helix helps make fibres like in your nails, e.g. Keratin.
The beta pleated-sheet helps make the strength giving protein in silk, fibroin.
Many proteins are made from both alpha-helix and beta-pleated sheet.
Fibrous proteins
A fibrous protein only achieves a secondary structure .
The simple alpha-helix polypeptides do not undergo further folding.
Structure of a fibrous protein
d elix ure
Page 43
Tertiary protein structure
This is when a polypeptide is folded into a precise shape.
The polypeptide is held in ‘bends’ and ‘tucks’ in a permanent shape by a range of bonds including:
Disulphide bridges [sulphur-sulphur bonds]
Hydrogen bonds
Ionic bonds.
Page 44
Tertiary protein structure
Page 45
Quaternary protein structure
Some proteins consist of different polypeptides bonded together to form extremely intricate shapes.
A haemoglobin molecule is formed for separate polypeptide chains.
It also has a haem group, which contains iron.
The inorganic group is known as the prosthetic group.
In haemoglobin it aids oxygen transport.
Page 46
Quaternary protein structure
How useful are proteins?
Cell membrane proteins: Transport substances across the membrane for processes such as facilitated diffusion and active transport.
Enzymes: Catalyse biochemical reactions, e.g. pepsin breaks down protein in to polypeptides.
Hormones: are passed through the blood and trigger reactions in other parts of the body e.g. insulin regulates blood sugar.
Immuno-proteins: e.g. antibodies are made by lymphocytes and act against antigenic sites on microbes.
Structural proteins: give strength to organs, e.g. collagen makes tendons tough.
Page 49
Transport proteins: e.g. haemoglobin transports oxygen in the blood.
Contractile proteins: e.g. actin and myosin help muscles shorten during contraction
Storage proteins: e.g. aleurone in seeds helps germination, and casein in milk helps supply valuable protein to babies.
Buffer proteins: e.g. blood proteins, due to their high charge, help maintain the pH of plasma.
Page 50
Enzymes
Living cells carry out many biochemical reactions.
These reactions take place rapidly due to enzymes.
All enzymes consist of globular proteins.
Page 51
Enzymes
The tertiary folding of polypeptides are responsible for the special shape of the ‘active’ site.
Some enzymes require additional non-protein groups to enable them to work efficiently. e.g the enzyme dehydrogenase needs coenzyme NAD to function.
Page 52
The lock and key theory
Substrate Enzyme
+
Enzyme-substrate complex
A catabolic reaction [substrate broken down]
enzyme-substrate
complex
oducts
An anabolic reaction
[substrates used to build a new molecule]
substrate
Page 55
Anabolic reaction continued
Enzyme substrate complex
Page 56
Metabolic reactions
Metabolic reactions = anabolic reaction + catabolic reaction.
Metabolism is a summary of build up and break down reactions.
Page 57
Induced fit theory
The active site is a cavity of a particular shape.
Initially the active site is not the correct shape in which to fit the substrate.
As the substrate approaches the active site, the site changes and this results in it being a perfect fit.
After the reaction has taken place, and the products have gone, the active site returns to its normal shape.
Page 58
Induced fit theory
Enzyme Sustrate
+
Induced fit continued
In
pr
enzyme
Page 61
Lowering of activation energy
Every reaction requires the input of energy.
Enzymes reduce the level of activation energy needed as seen in the graph.
substrate
Reaction without enzyme
Reaction with enzyme
products
Progress of reaction e
n e r g y
Page 62
Two minute summary
Now you have seen the presentation !
Summarise the most important points of this presentation.
What was the ‘muddiest’ point in the presentation?
Hand in your paper to the teacher before you leave the classroom.
Page 63
END OF PRESENTATION by S S Khalsa [science PGCE]
Page 64
This powerpoint was kindly donated to www.worldofteaching.com
http://www.worldofteaching.comis home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.
