1.6 Proteins Flashcards
What are amino acids
Basic monomer units which combine to make up a polymer called a polypeptide.
What can polypeptides be combined to make
A protein
How many amino acids occur naturally in protein
20 out of 100 amino acids
These 20 amino acids occur in all living organisms- which provides evidence for evolution
Each amino acid has a central carbon atom which connects to four different chemical groups
What are they
. An amino group (-NH2)
Basic group that gives it its name
. Carboxyl group (-COOH)
Acidic group which makes it acidic
. Hydrogen atom (-H)
. R group
Which Is a variety of different chemical groups. Each amino acid has a different R group
. Amino acids only differ in their R groups
What bond is formed between amino acid monomers to form a dipeptide
Peptide bond
What type of reaction is it when a dipeptide is formed
. Condensation reaction: a molecule of water is removed from the reaction
How is the water molecule made from amino acids bonding
What bond forms between them
Condensation reaction:
The OH from carboxyl group of one amino acid and a H from the amino group of another amino acid
A peptide bond forms between them
These make H2O
How can the peptide bond be broken
Hydrolysis, adding a molecule of water , to give two constituent amino acids
What is the primary stage of proteins
Polypeptides:
. Amino acid monomers joined together in polymerisation
. The sequence of amino acids in a polypeptide chain forms primary structure of any protein
====================
Why are there many types of primary protein structure
. The 20 naturally occurring amino acids join in different sequences so there are loads of possible combinations
What does the primary structure of a protein determine
. It ultimate shape and hence its function
. A change in a single amino acid in the primary sequence can change the shape of the protein stop it carrying out its function
What is the secondary structure of proteins
. Linked amino acids that make up polypeptides possess both NH and -C=O groups.
These groups have opposite charges due to oxygen having - charge and H having + charge
. These groups form hydrogen bonds
\ \ / /\ \ / /\ \
\ \ / / \ \ / / \ \
\ \/ / \ \ / / \ \
\/ \/ \ \
The shape can be an alpha helix or beta sheets, but both are formed by hydrogen bonds
What do the hydrogen bonds on secondary structure of proteins cause
Cause long polypeptide chain to be twisted into a long 3D shape like the coil on an alpha helix
What is the tertiary structure of proteins
The alpha helixes of secondary protein can be twisted and folded even more to give complex 3D structure of each protein
This structure is maintained by a number of different bonds. Where the bonds occur depend on the primary structure
Looks like a knot a bit
What 3 types of bonds are found on tertiary structure
. Disulphide bridges: Fairly strong and not easily broken
. Ionic bonds: Formed between carboxyl and amino groups that aren’t involved in forming peptide bonds.
They’re weaker than disulphide bonds and are easily broken by changes in PH
.Hydrogen bonds: Numerous but easily broken
What is the quaternary structure of proteins
Large proteins form complex molecules containing lots of individual polypeptide chains linked in various ways.
There can be non proteins (prosthetic groups) associated with the molecules also
How do you test for proteins
Biuret test: Detects peptide bonds
. Place a sample of the solution to be tested in a test tube and add an equal volume of sodium hydroxide solution at room temp
. Add a few drops of dilute copper sulfate solution, and mix gently
. Purple colouration indicates peptide bonds being present, and hence a protein
If no protein is present solution remains blue
What function do fibrous proteins have
Give the example
. Eg collagen, have structural functions
Structure of fibrous proteins
. Form long chains which run parallel to each other so cross bridges link them together.
This makes them very stable
What is the primary structure of collagen
. Unbranched polypeptide chain
Secondary structure of collagen
. Polypeptide chain is very tightly wound
The amino acid glycine is present as every 3rd amino acid helps tight packing
Tertiary structure of collagen
. Chain is twisted into a second helix
Quaternary structure of collagen
. Made up of 3 polypeptide chains wound together in the same way as individual fibres are wound together in a rope
Hydrogen bonds keep it together
What are globular proteins
Eg enzymes and haemoglobin carry out metabolic functions
Shape of globular proteins
Spherical, glob shape
Solubility of globular proteins, why?
Soluble in water
Because some amino acids have hydrophilic R groups that are attracted to water
. They have hydrophilic amino acids on their surface, so they interact with water molecules
The hydrophobic amino acids are in the centre of the protein, away from water
Name the 4 types of body proteins
Structural proteins, enzymes, antibodies, hormones
Describe the structure of antibodies
Globular proteins: Two pairs of polypeptide chains eg 2 long and 2 short
What do channel proteins do
How does its structure relate to its function
Its primary function is to transfer ions and water molecules through the membrane:
Involved in substances entering and leaving the cell
It has a hydrophilic and a hyrophobic side so one side attracts water nd the other repels water.
This allows the protein to fold up and form a channel through the cell membrane where the water soluble molecules can pass through
Where is collagen found
Tendons: which join muscles to bones
