Proteins Flashcards
What are globular proteins?
Proteins formed by compact amino acid chains, then folded into intricate chains that resemble spheres
Are globular proteins soluble or insoluble?
Soluble
Give an example of a globular protein
Insulin
Where is insulin produced?
In the pancreas
What does insulin do?
It aids the bodies ability to regulate energy and metabolise sugars
What does insulin illustrate?
A proteins ability to act as a biological messenger
What can proteins act as?
Biological transport mechanisms, biological messengers and they can play a role in the structure of animal cells
What are conjugated proteins?
Proteins that function in interaction with other chemical groups
How are conjugated proteins attached?
By weak covalent bonds
Are conjugated proteins soluble or insoluble in water?
Soluble in water
What are proteins?
Long chains of amino acids
Give an example of a conjugated protein
Haemoglobin and catalase
What are fibrous proteins?
A protein with an elongated shape, forming a rod or wire like shape
What do fibrous proteins provide?
Structural support for cells and tissues
Give examples of fibrous proteins
Keratin, elastin and collagen
Are fibrous proteins insoluble or soluble in water?
Insoluble
What enzymes break down proteins?
Protease enzymes
What is a prosthetic group?
A non-protein component in globular proteins
What are proteins without a prosthetic group called?
Simple proteins
What is formed when a lipid and a protein combine?
A lipoprotein
What is formed when a carbohydrate combines with a protein?
A glycoprotein
What is a cofactor?
A prosthetic group formed by metal ions and vitamins
Give an example of a prosthetic group
A haem group which contains an iron ion
What contains a haem group?
Catalase and haemoglobin
What bonds form between amino acids?
Peptide bonds
How does the protease enzyme denature the protein?
It breaks the bonds, altering the structure, it first breaks the hydrogen bonds, then the ionic bonds and then the disulphide bridges
What changes in the structure of amino acids?
The R group, but all amino acids have the same general formula
What are the four structures of proteins?
- primary structure
- secondary structure
- tertiary structure
- quarternary structure
How many naturally occurring amino acids are there?
20, each with there own R group
How is a polypeptide chain formed?
Condensation reactions when amino acids are added to a dipeptide
How many polypeptides does one protein consist of?
One polypeptide chain
What is polymerisation?
The process by which condensation reactions take place to form a polypeptide from amino acids
What are the types of proteins?
- Structural
- Catalytic
- Signalling
- Immunological
What are structural proteins?
They are the main component of body tissues such as muscles, skin, hair and ligaments
What are catalytic enzymes?
All enzymes are proteins catalysing many biochemical reactions
What are signalling proteins?
Hormones and receptors (many of these are proteins)
What are immunological proteins?
Antibodies
Where is a disulphide bridge formed?
Between two cystine amino acids
What does the primary structure look like?
A long chain of amino acids joined by polypeptide bonds
What does the primary structure of the protein determine?
It’s shape and function
What are the two secondary structures?
Alpha helix and beta pleated
What bonds do the secondary structure contain?
Weak hydrogen bonds
How are weak hydrogen bonds formed?
Between the positive charge on the hydrogen and the negative charge on the oxygen
What do the hydrogen bonds cause in the secondary structure?
The long polypeptide chains to twist into a 3D helix
What is the tertiary structure?
The 3D protein structure which is further folded and twisted to give it a more complex 3D structure
How in the tertiary structure maintained?
- Disulfide bonds
- Ionic bonds
- hydrogen bonds
What are disulphide bonds?
Bridges formed between cystine, they are strong and difficult to break
What are ionic bonds?
Bonds formed between carboxyl and amino groups that are not involved in the formation of peptide bonds, they are weaker than disulphide bridges
What are hydrogen bonds like?
Hey are numerous but they are weak and easily broken
What is the bond between two amino acids?
A dipeptide bond
How are peptide bonds formed?
The joining of amino acids by a condensation reaction
What are the four groups in an amino acids?
- Amino group
- Carboxyl group
- Hydrogen atom
- R side group
Where does the peptide bond form?
Between the carbon atom of one amino acid and the nitrogen atom of another
Where is the water produced in the condensation reaction
The OH from the carboxyl group and the H from the amino group
What is the process of the formation of a polypeptide
Polymerisation
Why can hydrogen bonds form between proteins?
The NH group has an overall positive charge whilst the O has an overall negative charge so they are therefore polar
What is the test for proteins?
The biuret test
What does the biuret test detect?
Peptide bonds
How do you carry out the biuret test?
- Place a sample of the solution in a test tube and add equal volume of sodium hydroxide solution at room temperature
- Add a few drops of very dilute (0.05%) copper (II) sulfate solution and mix gently
What result identifies a protein?
Purple coloration
What is the negative result?
The solution remains blue
What is the primary structure of collagen?
An unbranded polypeptide chain
What is the secondary structure of collagen?
Very tightly wound
What is the tertiary structure of collagen?
The chain is twisted into a second helix
What is the quarternary structure of collagen?
Three polypeptide chains would together
Where is collagen found?
Tendons
How do autotrophic green plants produce amino acidsz?
As a product of photosynthesis
How do heterotrophic organisms gain their amino acids?
From plants through food chains
What do simple proteins have in their structure?
Only amino acids
Give examples of simple proteins
Albumins, globulins and scleroproteins
What do conjugated proteins contain?
Amino acids and some other type of chemical molecule
What is the prosthetic group in a a nucleoprotein?
Nucleic acids
What is the prosthetic group in a phosphoprotein?
Phosphoric acid
What is the prosthetic group in lipoprotein?
A lipid
What does haemoglobin contain?
4 poly peptide chains each of which has a porphyrin ring which contains the iron ion
What does pH affect?
How the amino acids and proteins ionise
How does the carboxylic acid group ionise?
RCOOH <=> RCOO- + H+
How does the amino group ionise?
RNH2 + H+ <=> RNH3+
How does a high pH effect the ionisation of the carboxylic acid?
The reaction will be pushed to the left
How does a high pH effect the ionisation of the amine group?
The reaction will be pushed to the right
In a high pH environment with the amino acids be positively or negatively charged?
The amino acids will predominantly be positively charged cations
How does a low pH effect the ionisation of the carboxylic acid?
The reaction will be pushed to the right
How does a low pH effect the ionisation of the amine group?
The reaction will be pushed to the left
In a low pH environment with the amino acids be positively or negatively charged?
The amino acids will predominantly be negatively charged anions
When will a zwitterion form?
When there is an intermediate hydrogen ion concentration where the forward and the backwards rates of reaction for the ionisation of the carboxylic acid and the ionisation of the amine group are equal
Why will a zwitterion form?
Because the amino acid will carry 50% of the amine groups uncharged and 50% of the amine groups charged and will carry 50% of the carboxylic acid group charged and 50% of the carboxylic acid group uncharged
What will pH of zwitterion formation dictate?
The isoelectric point
Why do different enzymes have different optimum pH’s?
Because the isoelectric point is different for each specific amino acid or protein
What is the iso-electric point?
The pH at which the amino acids or protein carry no net charge/ carry equal amounts of negative and positive charges
Will the charge on the active sites of an enzymes affect the capability of the enzyme to join with its specific substrate?
Yes, that’s why enzymes tend to work best at specific pH’s
How does pH affect solubility?
At the IEP opposite charges attract making protein molecules clump together and precipitate. At other pH’s the protein will only carry like charges which will repel molecules from each other which can increase the solubility.
What happens to proteins at extremes of pH
The protein molecules will carry huge numbers of like charges (as the ionisations of the amine groups and the carboxylic acid groups will go almost to completion). These charges may exert a large repulsive force which breaks apart the hydrogen and ionic bonds holding the 3D structure together. Therefore the 3D structure therefore breaks apart and the protein is denatured.
What is denaturation?
The loss of function of a protein caused by a loss of structure
As well as ph what is another agent of denaturation?
Heat
How does heat cause denaturation
It can disrupt the hydrogen and ionic bonds therefore causing the 3D structure to unravel.
At what temperature do most proteins denature?
45 degrees
Which bonds in proteins can withstand the higher temperatures?
Sulphur bonds therefore proteins containing the most sulphur bonds can withstand the highest of temperatures
What are the functions of proteins?
- Structural proteins
- Enzymes
- Hormones
- Contractile proteins
- Storage proteins
- Transport proteins
- Protective proteins
- Buffers
- Osmotic proteins
- Toxins
Give examples of structural proteins
- Collagen
- Elastin
- Keratin
- Lipoproteins
- Fibroin
- Sclerotin
- Mucoproteins
Give examples of enzymes
- hydrolases such as; amylase, proteases and lipases used in digestion
- oxido-reductases such as the dehydrogenase used in the metabolic cycle and ligases
Give examples of hormones
- somatotropin
- pituitary growth hormone
- insulin
Give examples of contractile proteins
- actin
- myosin
- dynein
Give examples of storage proteins
- ovalbumin
- casein
- lactalbumins
- glutelins
- gliadins
- ferritin
Give examples of transport proteins
- haemoglobin
- myoglobin
- plasma albumin
- transferritin
- binding globulins
Give examples of protective proteins
- thrombin
- fibrinogen
- antibodies
Give an example of a buffer
Haemoglobin
Give an example of an osmotic protein
Plasma albumin
Give examples of toxins
- phospholipase
- clostridium tetani
- clostridium botulinum
- diphtheria
- ricin
What is the function of ligases?
They enable molecules to be bond together using energy from ATP
Where is actin and myosin found?
Muscles
What does dynein make up?
The structure of cilia and flagella
Why can’t amino acids be stored as just amino acids?
Because of the toxic amine groups
How do you store amino acids?
As proteins
What is ovalbumin, casein and lactalbumin?
Milk proteins
What are glutelins and gliadins?
Cereal seed proteins
What is ferritin?
A protein that binds up iron and stores it in the spleen, liver and red bone marrow
How do transport proteins work?
By binding onto and releasing insoluble or inadequately soluble substances so they can be transported through the body
What does haemoglobin do?
Transports oxygen in vertebrate blood
What does myoglobin do?
Transports oxygen in muscles
What does plasma albumin do?
Transports fatty acids in the blood
What does transferritin do?
Transports iron through blood to the iron storage sites
What do binding globulins do?
Transports insoluble thyroid hormones through the blood
What are thrombin and fibrinogen?
Blood clotting factors which reduce bleeding during injury
What are antibodies?
Proteins that react with antigens to neutralise them therefore giving protection against disease
What is a buffer?
A substance that is resistant to changes in pH
How does haemoglobin work as a buffer?
It reacts with hydrogen ions to form reduced haemoglobin which can buffer blood between 7.2 and 7.6
How does plasma albumin work?
It maintains blood volume by maintaining the water level in blood plasma. Cell sap has the same role in plants
What are phospholipases?
Enzymes found in snake venom which destroy cell membranes
What are clostridium tetani, clostridium botulinum and diphtheria?
Bacteria that release toxic chemicals, harmful to humans
What is ricin?
A toxic chemical that can cause jaundice
What elements are present in proteins?
Carbon, hydrogen, oxygen and nitrogen are present (without including elements present in R groups)
