1. Proteins have a very wide range of functions in living organisms.
Topic 2.4
IB Biology
Miss Werba

2. TOPIC 2 – MOLECULAR BIOLOGY
2.1
MOLECULES TO METABOLISM
2.2
WATER
2.3
CARBOHYDRATES & LIPIDS
2.4
PROTEINS
2.5
ENZYMES
2.6 STRUCTURE OF DNA & RNA
2.7 DNA REPLICATION, TRANSCRIPTION & TRANSLATION
2.8 CELL RESPIRATION
2.9 PHOTOSYNTHESIS
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3. THINGS TO COVER U.1 U.2 U.3 U.4 U.5 U.6 U.7 U.8 Statement Guidance
Amino acids are linked together by condensation to form polypeptides.
U.2
There are 20 different amino acids in polypeptides synthesized on ribosomes.
Most organisms use the same 20 amino acids in the same genetic code although there are some exceptions. Specific examples could be used for illustration.
U.3
Amino acids can be linked together in any sequence giving a huge range of possible polypeptides.
U.4
The amino acid sequence of polypeptides is coded for by genes.
U.5
A protein may consist of a single polypeptide or more than one polypeptide linked together.
U.6
The amino acid sequence determines the three-dimensional conformation of a protein.
U.7
Living organisms synthesize many different proteins with a wide range of functions.
U.8
Every individual has a unique proteome.
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4. THINGS TO COVER Statement Guidance A.1 A.2 S.1 NOS 3.1
Rubisco, insulin, immunoglobulins, rhodopsin, collagen and spider silk as examples of the range of protein functions.
The detailed structure of the six proteins selected to illustrate the functions of proteins is not needed.
A.2
Denaturation of proteins by heat or by deviation of pH from the optimum.
Egg white or albumin solutions can be used in denaturation experiments.
S.1
Drawing molecular diagrams to show the formation of a peptide bond.
NOS 3.1
Looking for patterns, trends and discrepancies
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5. POLYPEPTIDES
U.4
S.1
Amino acids are linked together by condensation to form polypeptides.
The bonds formed are covalent.
The bonds formed are peptide bonds.
The bonds form in the ribosomes.
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6. POLYPEPTIDES
U.4
S.1
Peptide bond:
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7. ESSENTIAL AMINO ACIDS
U.2
There are 20 essential amino acids found in polypeptides synthesised by the ribosomes.
The source of these amino acids would be the absorbed products of digestion.
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8. ESSENTIAL AMINO ACIDS
U.2
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9. PEPTIDE SYNTHESIS
U.2
Ribosomes are the molecules (structures) within cells that facilitate the formation of peptide bonds.
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10. POLYPEPTIDES There are infinite possibilities for polypeptides
U.3
There are infinite possibilities for polypeptides
20 amino acids in any order or combination or length
A 7 amino acid peptide has 1,280,000,000 possible combinations.
Some polypeptides (eg. titin) are 30,000 amino acids in length!
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11. POLYPEPTIDES The sequence of amino acids is coded for by genes.
DNA stored in the nucleus is read and “transcribed” into an RNA message.
This RNA message (mRNA) can leave the nucleus and head to the ribosomes.
Here, the instructions contained within the message are “translated” into a polypeptide.
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12. Each amino acid has unique properties.
POLYPEPTIDES
U.6
Each amino acid has unique properties.
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13. POLYPEPTIDES
U.6
U.5
The properties of each amino acid influence how a polypeptide will be able to fold up into a protein.
There are four levels of structure in proteins:
Primary structure
Secondary structure
Tertiary structure  folding gives the tertiary structure of a protein
Quaternary structure
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14. PROTEIN STRUCTURE Primary (1˚) structure: Secondary (2˚) structure:
Amino acid sequence
Involves peptide bonds
Secondary (2˚) structure:
Repeating local structures
Generally found in fibrous proteins
These include:
α-helices: peptide chain wound into a helix
β-pleated sheets: peptide strands lie in a plane
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15. PROTEIN STRUCTURE Tertiary (3˚) structure: Quaternary (4˚) structure:
Single protein folds into a 3D shape
Generally form globular proteins
Important for function of the protein
Quaternary (4˚) structure:
Two or more polypeptide chains linked together
eg. Hemoglobin subunits becoming haemoglobin
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16. FIBROUS & GLOBULAR PROTEINS
Proteins can be separated into two groups based on their shape:
Fibrous Globular
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17. FIBROUS & GLOBULAR PROTEINS
FIBROUS PROTEINS
GLOBULAR PROTEINS
SOLUBILITY
(usually) insoluble
(usually) soluble
SHAPE
Long, narrow shape
(strands/sheets)
Rounded shape
SENSITIVTY TO CHANGES
Less sensitive to changes in pH/temperature/salt
More sensitive to changes in pH/temperature/salt
ROLE
Have structural roles
Have functional roles
EXAMPLES
keratin / fibrin / elastin / collagen / actin / myosin
insulin / immunoglobulin / haemoglobin / amylase / Na+/K+ pump
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18. PROTEIN FUNCTIONS Proteins have a variety of uses in organisms:
Catalysis – speeds up chemical reactions – Rubisco
Muscle contraction
Cytoskeletons – give animal cells their shape
Tensile strengthening – provide strength – collagen
Blood clotting
Transport of nutrients and gases
Cell adhesion
Membrane transport
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19. PROTEIN FUNCTIONS Proteins have a variety of uses in organisms:
Hormones – insulin
Receptors – binding sites in membranes and cytoplasm for hormones, neurotransmitters, tastes, smells and receptors for light – rhodopsin
Packing of DNA
Immunity – immunoglobulins
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20. PROTEIN FUNCTIONS: Rubisco
A.1
Full name = ribulose bisphosphate carboxylase
It is an enzyme involved in photosynthesis
It “fixes” carbon from a gaseous state to one able to be utilised by the plant.
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21. PROTEIN FUNCTIONS: Insulin
A.1
It is a hormone involved in maintaining glucose levels in the blood within narrow limits.
It is secreted by the β cells in the pancreas.
Insulin signals the liver cells to absorb glucose and convert it to glycogen.
This takes it out of the bloodstream.
Not produced by people with type I diabetes.
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22. PROTEIN FUNCTIONS: Immunoglobulins
A.1
Also known as antibodies
Produced by the immune cells in response to the presence of an antigen
The binding site of the protein is highly variable allowing them to respond to a range of pathogens.
They also signal other immune cells to help destroy the pathogen once it has been identified.
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23. PROTEIN FUNCTIONS: Rhodopsin
A.1
A pigment that can absorb light.
Found in rod cells within the retina at the back of the eye.
The absorption of light causes a chemical and conformational change to the molecule.
This results in a nerve impulse being sent to the brain.
Rods work well in even dim light, and are responsible for monochrome vision.
rhodopsin
mitochondria
nucleus
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24. PROTEIN FUNCTIONS: Collagen
A rope-like structural protein.
Forms a mesh of fibres in skin and in the blood vessel walls that resists tearing.
Gives tendons, ligaments, skin and blood vessel walls their strength.
Forms part of teeth and bones, preventing cracks and fractures.
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25. PROTEIN FUNCTIONS: Spider silk
A.1
Fibrous proteins
Spiders can produce different types of silk with different properties for different purposes.
Some of the silk is comparable to steel in regards to its tensile strength.
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26. PROTEOME Every individual has a unique proteome.
Proteome: a term given to all of the proteins produced by a cell, tissue or an organism.
The proteome is a function of both the organism’s genome (genes) and environmental factors.
Environmental factors such as nutrition, temperature, etc can affect a cell’s activities
Epigenetics: field of study of how much influence the environment has on the genome of an organism
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27. PROTEOME eg. DNA methylation can stop translation!
U.8
eg. DNA methylation can stop translation!
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28. https://youtu.be/kp1bZEUgqVI

29. PROTEIN DENATURATION
A.2
High temperatures or extremes of pH (high or low) can cause denaturation of proteins.
Denaturation affects the bonds holding the secondary, tertiary and quaternary structures together.
This will result in an irreversible loss of shape and therefore function.
eg. Cooking an egg denatures its proteins, causing them to harden
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30. Determine the temperature stability of albumen.
PROTEIN DENATURATION
A.2
Determine the temperature stability of albumen.
Available equipment:
Electronic hot plates (for water baths)
Albumen (egg white)
Thermometers
Beakers
Test tubes
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31. PROTEINS The interaction of polypeptide subunits and prosthetic groups
Q1 Which best describes the tertiary structure of a protein?
The interaction of polypeptide subunits and prosthetic groups
Interactions forming hydrogen bonds between the amino acids
The sequence of amino acids in the polypeptide chain
The structure formed from interactions between the amino acid side groups
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32. PROTEINS
Q2 Other than acting as catalysts state three functions of proteins, giving an example of each [3]
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