Proteins + Lipids Flashcards
Where does the bonding form in a polypeptide chain
These bonds form between the R groups of the amino acids on a polypeptide chain
This means that the type of bonding depends on the specific amino acids present in the polypeptide
state the bonding present in/important for tertiary and quaternary structure of proteins
Hydrogen bonding
Hydrophobic and hydrophilic interactions
Ionic
Disulphide bonds
describe hydrogen bonding
Type of bonding:
Hydrogen bonding - with two amino acids with R groups containing a hydroxyl.
Due to slight positive and negative charges present on the hydroxyl, a hydrogen bond can form between these two R groups
This contributes to the 3D shape of polypeptide chain
hydrogen bonds are weak - easily broken by high temp or by pH changes
describe hydrophobic and hydrophilic interactions
Several amino acids have uncharged R groups
These are called non-polar amino acids
Non-polar amino acids are not attracted to water
These are amino acids are hydrophobic
Amino acids with hydrophobic R groups tend to cluster together
By doing this they can exclude water molecules
These are called hydrophobic interactions
hydrophobic interactions tend to be found in the centre of proteins, well away from any water molecules
hydrophilic amino acids tend to be found on the surface of proteins where they can interact with water molecules
like hydrogen bonds, hydrophobic and hydrophilic interactions are relatively weak bonds
describe ionic bond
protein struture
Ionic bonds are found between amino acids with charged R groups/carboxyl and amino groups that are not involved in forming peptide bonds
e.g. with two amino acids on a polypeptide chain - one of the amino acids has a positively charged R group and the other has a negatively charged R group
These oppositely charges attract each other and form an ionic bond
This ionic bond holds different parts of the polypeptide chain together and contributes to the structure of the protein
ionic bonds are broken by changes in pH
one reason why enzymes can denature under acidic or alkaline conditions
describe disulphide bonding
In a polypeptide containing two molecules of amino acid called cysteine
R group of cysteine contains a sulfur atoms – occur/found between with amino acids with R groups containing sulfur
The sulfur atoms in the two cysteine molecules can form a covalent bond
which is called a disulfide bond
disulfide bonds are relatively strong - not broken by high temperatures or pH changes
What protein structure are these bonds involved in -
what does it depend on
If these bonds form between amino acids on the same polypeptide chain, then they are involved in the tertiary structure
But if they form between amino acids on different subunits/polypeptide chains then they are also involved in quaternary structure
types of proteins
globular proteins
fibrous proteins
describe the features of globular proteins
blob circle for simplified structure
Tend to have an approximately spherical shape
SOLUBLE IN WATER
Contain amino acids which have R groups which are attracted to water - hydrophilic amino acids
Globular proteins have got hydrophilic amino acids on their surface
Means that the hydrophilic R groups can interact with water molecules
which makes globular proteins soluble in water
hydrophibic amino acids - amino acids which have R groups which are not attracted to water
in globular proteins -hydrophobic amino acids are found deep in the centre of the protein - well away from any water molecules
examples of globular proteins
haemoglobin
insulin
lysosome
describe the structure of fibrous proteins
unlike globular proteins, fibrous proteins often play a structural role e.g. in bones or tendons or in the walls of blood vessels such as arteries
fibrous proteins tend to form long rope-like molecules
have a large proportion of amino acids with hydrophobic R groups
means that unlike globular proteins, fibrous proteins are insoluble in water
examples of fibrous proteins
collagen
keratin
elastin
lipdids
scientific name for molecules found in fats and oils
describe the functions of lipids
a major source of energy in the human diet – e.g. lipids are found in oils such as olive oil and in solid fats such as butter - both are rich sources of energy
SOURCE OF ENERGY - when oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water
lipids are used to store energy e.g. adipose tissue in humans. adipose tissue is found under the skin.
As well as acting as an energy store, this adipose tissue also helps to insulate the body, reducing heat loss to the environment
INSULATION - Fats are slow conductors of heat and when stored beneatht he body surface help to retain body heat - also act as electrical insulators in the myelin sheath around nerve cells
adipose tissue - fat is found around delicate internal organs such as kidneys - this helps to protect these organs from injury
Used as waterproofing - lipids are insoluble in water and therefore useful as waterproofing
e.g. the oils which coat the feathers of aquatic birds
lipids are a major part of the structure of membranes such as those which surround cells and mitochondria
phospholipids contribute to the flexibility of memrbanes and the transfer of lipid-soluble substances across them
fats are solid at room temp (10 to 20 degrees) wheras oils are liquid
state the two main types of lipids
triglycerides
phospholipids
