Proteins Flashcards
Proteins : elements, monomer, function
CHON(S), Amino acids, structural fibres, enzymes, hormones, antibodies,
Primary structure
A sequence of amino acids in a polypeptide chain held together by peptide chains. Different sequences of amino acids form different proteins in primary structure.
Secondary structure
Hydrogen bonds that form between the NH and CO groups of the amino acids make the chain coil into an alpha helix or fold into a beta pleated sheet
Tertiary structure
Coiled or folded chains are folded and coiled Further. more bonds are formed between parts of the polypeptide chains. Forming a 3-D structure.
Ionic bonds in proteins
attractions between negatively charged R groups and positively charged R groups on different parts of the molecule
Disulphide bonds in proteins
Whenever two molecules of the amino acid cysteine come close together the sulphur atom in one cysteine bonds to the other one
Hydrophobic and hydrophilic interactions
When hydrophobic (Water repelling) our groups are close together in protein they tend to clump together inside the molecule away from water. This means that hydrophilic (water attracting) all groups are more likely to be pushed to the outside which affects how the protein folds up into its final structure
Hydrogen bonds in protein
These weak bonds form between slightly positively charged hydrogen atoms in an R group and slightly negative charged atom in another R group of the polypeptide chain
Quaternary structure
Made of several polypeptide chains held together by cross-link covalent bonds.
Globular proteins
- are round and compact
- The hydrophilic R groups on the amino acids are pushed to outside of the molecules
- this makes globular protein soluble
- so they are easily transported in fluids
- metabolic function
- can be conjugated ( contains a non-protein group (prosthetic group)
- Irregular amino acid sequence To
- more sensitive to changes eg in heat or pH
Fibrous proteins
- Tough and long and narrow rope shaped
- Strong and insoluble
- Are structural proteins so fairly unreactive
- few repetitive amino acid sequence
- Less sensitive to changes eg in heat or pH
Globular protein examples
Haemoglobin, insulin, Amylase
Fibrous protein examples
Collagen, keratin, elastin, actin
Structure and function of Haemoglobin
- globular
- carries oxygen around the body in red blood cells.
- It is known as a conjugated protein
- all four polypeptide chains in haemoglobin has a prosthetic group called haem
- it contains iron which oxygen binds to.
- it is soluble
What is the function and structure of Insulin (globular)
- it is a hormone that regulates the blood glucose level secreted by the pancreas.
- Its soluble meaning it can be transported in the blood to the tissue to act
- consist of two polypeptide chains which are held together by disulphide bonds
- when they’re in the pancreas, six of these molecules bind together to form large globular structure.
Function and structure of Amylase (globular)
- Amylase is an enzyme that catalyses the
Hydrolysis of starch in the digestive system. - It is made of a single chain of amino acid
- in secondary structure contains both alpha and beta sheets
- are globular proteins.
- is soluble
Function and structure of Collagen (fibrous)
- forms animal connective tissues such as bone skin and muscle.
- It is a very strong molecule so not soluble
- minerals can bind to the protein to increase its rigidity eg in bones.
- forms a triple helix then a fibre
- made mostly of glycine
Function and structure of Keratin
- fibrous
- Found in many of the external structures of animals such as skin, hair, nails, feathers, and horns
- it can be flexible eg skin or hard and tough eg nails so not soluble
Function and structure of Elastin (fibrous)
- Found in elastic connective tissue such as skin, large blood vessels and some ligaments
- It is elastic so allows tissues to recoil to their original shape after being stretched
Explain how the globular structure of haemoglobin makes it suited to its function
The hydrophilic side chains are on the outside of the molecule meaning it is soluble in water which makes it a good transport for oxygen in the blood
What is meant by glycoprotein?
A protein combined with a carbohydrate
Explain how the structure of collagen contributes to its strength And how it suited to its function
Many hydrogen bonds and many strong covalent bonds which keep triple helix together, contains amino acids which form a tight coiled helix which form fibers. This means it can form strong rigid structures like bone
State 4 properties of a globular protein that are different to those of a fibrous protein
Soluble
reactive
Has many different amino acids
Can contain a prosthetic group
Explain how the structure of insulin makes it soluble
The hydrophobic R groups on the amino acids of the insulin clump together causing the hydrophilic groups to be pushed to the outside of the molecule making it soluble
How to test for a protein
Add a few drops of biuret Regent (Sodium hydroxide and copper sulphate) to the sample, a change from Blue to purple is a positive result
Compare the bonding in secondary and tertiary structure of a protein
Secondary structure only has hydrogen bonds but tertiary structures also contain ionic sulphide hydrophobic and hydrophilic interactions
what part of amino acids are involved in condensation to form primary structure of a protein
Amine group and carboxyl group
A student uses Biuret test to detect the presence of Enzymes, How is the structure of enzyme allowing it to be detected
Enzymes are globular proteins the hydrophilic or groups on the outside
a doctor suspects haemoglobin in the urine, How can they confirm
haemoglobin is a protein used the biuret test which goes from blue to purple if present
examples of proteins
enzymes, anti bodies, carrier proteins
Describe in detail how two amino acids bond
A peptide covalent bond would form by condensation between the C from the carboxyl group and the N from the amine group the OH from carboxyl group of one amino acid and the H from amine group from another amino acid form water molecule and release it
How do r groups Interact to determine the tertiary structure of a protein
- the S from one R group forms a disulfide bond to another S from a different R group
- hydrogen makes a hydrogen bond to a partially negative molecule
- Hydrophobic r groups repel water and therefore bundle up causing hydrophilic r groups to surround on the outside
