1. Proteins

2. WE SHALL LOOK AT PROTEIN SYNTHESIS.
CONSIDER PROTEIN STRUCTURE AT THE MOLECULAR LEVEL.
DISCUSS DIFERENT USES OF PROTEINS.
BREIFLY LOOK AT ENZYMES.

3. Protein synthesis
Protein synthesis is the making of proteins, using the information that is found in DNA (Chromosomes).
CELL
chromosomes
nucleus
ribosomes
ribosomes

4. Proteins Proteins are very important molecules for a cell.
Nucleus
The cell
Proteins are very important molecules for a cell.
Proteins are used to build cell structures and are used as enzymes.
Chromosomes

5. 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.

6. The cell
Nucleus
Piece of
DNA
Selected
For
study
chromosomes

7. DNA to see how its information
Nucleus
Let’s zoom in on
This short segment of
DNA to see how its information
Is used.
Piece of
DNA
Selected for
study

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

9. [Both sides are used for DNA Replication, to copy the Chromosome.]
Gene (information)
Unused strand
Only one side of the DNA
is used now.
[Both sides are used for DNA
Replication, to copy the
Chromosome.]

10. Forms, one subunit at a time, and Transcribes [copies] the genetic
RNA subunit
A single-strand of RNA
Forms, one subunit at a time, and
Transcribes [copies] the genetic
Information from the DNA.

11. The new strand is an RNA molecule
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 D N A
RNA

12. The RNA now has copied the subunit sequence of the gene.
The DNA is no longer needed in the process of protein synthesis. D N A D N A
RNA

13. The DNA ‘zips’ closed and remains in the nucleus
RNA
DNA double strand

14. Is called messenger RNA (now carrying the genetic ‘ message’).
Nucleus
This RNA molecule
Is called messenger RNA
(now carrying the genetic ‘ message’).
It will leave the nucleus and travel
To a ribosome to build a protein molecule.
RNA

15. Once the messenger RNA [mRNA]
At the ribosome
Code for one
Amino acid
Once the messenger RNA [mRNA]
Is at the ribosome, the genetic information will
be translated by ribosome to make a protein
mRNA
At the ribosome

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.

17. 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
Code for a
Particular amino acid

18. 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.

19. The tRNA matches up to the mRNA, Just like the two strands of DNA
Amino
acid
tRNA m R N A
The tRNA matches up to the mRNA,
Just like the two strands of DNA
Molecule match up.
The sequence of three subunits of the mRNA
Can only match up with one particular tRNA.

20. Amino acid m R N A

21. A different set of three mRNA subunits means a different
tRNA molecule. That means a different amino acid will be
Carried in.
Two different
Amino acids m R N A
Two different tRNA molecules

22. The two amino acids are linked By a peptide bond.
Between amino acids
The two amino acids are linked
By a peptide bond.
Then a tRNA molecule leaves
The ribosome.

23. Carry in the proper amino acid and the process will continue.
The next tRNA will
Carry in the proper amino acid
and the process will continue.

24. The chain of amino acids is called a ‘polypeptide’
And when it is very long it is called a protein.
polypeptide

25. A very short polypeptide chain, or part of a protein
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

26. The end of protein synthesis at the ribosome.

27. PROTEIN STRUCTURE 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.

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).

29. Before we can understand how proteins are constructed, the structure of amino acids needs to be considered.

30. R represents groups such as CH3 or C2H5
Carboxylic acid
group
Amine group
N C C H OH H
AN AMINO ACID

31. How are proteins constructed
First the Amino acids bond together.
They are joined together by what is known as a peptide bond.

32. Formation of a peptide bond via condensation.
H R O H R O
N C C N C C
H H H OH H OH
Amino acid
Amino acid

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

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.

35. 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.

36. 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.

37. Transport proteins: e.g. haemoglobin transports oxygen in the blood.
Contractile proteins: e.g. actin and myosin help muscles shorten during contraction
Buffer proteins: e.g. blood proteins, due to their high charge, help maintain the pH of plasma.

38. Enzymes Living cells carry out many biochemical reactions.
These reactions take place rapidly due to enzymes.
All enzymes consist of globular proteins.

39. Enzyme-substrate complex
The lock and key theory
Substrate Enzyme +
Enzyme-substrate complex

40. A catabolic reaction [substrate broken down]
enzyme-substrate
complex
2 x products
enzyme

41. An anabolic reaction [substrates used to build a new molecule]
enzyme
substrate

42. Anabolic reaction continued
Enzyme substrate complex
Single product formed
Enzyme ready to
Use again

43. Lowering of activation energy
Reaction without
enzyme
Every reaction requires the input of energy.
Enzymes reduce the level of activation energy needed as seen in the graph.
substrate
Reaction with enzyme e
nergy
products
Progress of reaction

44. END OF PRESENTATION