Proteins - globular and fibrous proteins Flashcards
what is a globular protein
molecules of a relatively spherical shape which are soluble in water and often have metabolic roles within the organism
how do globular proteins role up in a spherical shape
any hydrophobic R groups are turned inwards towards the centre of the molecule, while hydrophillic R groups are on the outside of the protein
why are globular proteins soluble in water
water molecules can easily cluster round and bind to them.
why is it important for globular proteins to be soluble
its essential for regulating many of the processes necessary for life (chemical reactions, immunity and muscle contractions)
what are examples of globular proteins
enzymes, hormones
what is haemoglobin an example of
a globular, conjugated protein
what is a conjugated protein
globular proteins that contain a non protein component called a prosthetic group
what is different about simple proteins
they dont have prosthetic groups
what is a prosthetic group
a non protein component that forms a permanent part of a functioning molecule
give examples of prosthetic groups
lipids or carbohydrates combine with proteins forming lipoproteins or glycoproteins
metal ions and molecules derived from vitamins also form prosthetic groups.
what is the prosthetic group in haemoglobin
haem
what does haem contain
iron (II) ion - Fe2+
what is the primary structure of hameoglobin
contains a wide range of amino acids connected together in a specific sequence of peptide bonds
what is the secondary structure of haemoglobin
most of the amino acids in haemoglobin form alpha helices connected by short beta-pleated sheet segments
what is the tertiary structure of haemoglobin
each polypeptide chain with haemoglobin contains a haem prosthetic group making it a conjugated protein
hydrophobic R groups migrate to the centre of the structure
hydrophillic R groups migrate to the outside of the structure
contains ionic bonds but no disulfide bridges
what is the quaternary structure of haemoglobin
has 4 subunits (polypeptide chains). 2 alpha units and 2 beta units
each polypeptide chain has its own tertiary structure but when fitted together form a haemoglobin.
how is haemoglobin able to effectively tranport oxygen around the body
each chain contains a haem prosthetic group capable of carrying a single oxygen molecule. it can pick up oxygen in the lungs and transport it to cells that need it, where its released. when oxygen binds to iron, haemoglobin turns from purple to red
where is haemoglobin found
within red blood cells and plays a vital role in transporting oxygen and carbon dioxide around the body
give properties of haemoglobin
its very flexible and soluble in water
what is catalase
a globular conjugated protein
an enzyme that catalyses the breakdown of hydrogen peroxide
describe the structure of catalase
a quaternary protein containing four haem prosthetic groups.
what does the presence of the iron (II) ions in the prosthetic groups allow catalase to do
allow catalase to interact with hydrogen peroxide and speeds up its breakdown.
what is hydrogen peroxide
a common byproduct of metabolism but is damaging to cells and cell components if allowed to accumulate.
what is insulin
a globular protein but its not conjugated
its a hormone
what is similiar about globular proteins
all globular proteins are compact and soluble in water as their hydrophobic R groups are kept away from the aqueous environment whilst the hydrophillic R groups are on the oustide of the protein
what is insulin involved in
the regulation of blood glucose concentration.
why must insulin be soluble
its a hormone that needs to be transported in the bloodstream. they have to fit into specific receptors on cell surface membranes to have their effect and therefore need to have precise shapes
how many polypeptide chains does insulin have
two
describe the structure of insulin
the A chains begins with a section of alpha helix and the B chain ends with a section of beta pleats. both chains fold in a tertiary structure and are joined by disulfide links. amino acids with hydrophillic R groups are on the oustide of the molecule making it soluble in water.
what does insulin bind to
glycoprotein receptors on the outside of muscle and fat cells to increase their uptake of glucose from the blood and also increase their rate of consumption of glucose
what are fibrous proteins
they have a relatively thin structure, insoluble in water and metabolically inactive often having a structural role within an organism
what are fibrous proteins made up of
long insoluble molecules. this is due to the presence of a high proportion of amino acids with hydrophobic R groups in their primary structure.
they contain a limited range of amino acids usually with small R groups. the amino acid sequence in the primary structure is usually quite repetitive
what does the repetitive sequence of amino acids in fibrous proteins allow them to form
to form fibres which have a structural function. this leads to very organised structures reflected in the roles they have. they tend to make strong, long molecules which aren’t folded into 3d shape
where is keratin present
in hair, skins and nails
what does keratin have a high proportion of
cysteine (contains sulfur)
this results in many strong disulfide bridges forming strong, inflexible and insoluble materials. the degree of disulfide bonds determines the flexibility - hair contains fewer bonds making it more flexible than nails.
where does the unpleasant smell when hair or skin is burnt come from
due to the presence of relatively large amounts of sulfur in these proteins
what does keratin provide
mechanical protection and an impermeable barrier to infection and being waterproof it prevents the entry of waterborne pollutants
where is elastin found
in elastic fibres (along with small protein fibres).
where are elastic fibres found
elastic fibres are present in the walls of blood vessels and in the alveoli of lungs - they give these structures the flexibility when needed but to also return to their normal size
how do elastic fibres help blood vessels
helps them stretch to maintain pressure wave of blood as it passes through
what is the primary structure of elastin
alternate hydrophobic and lysine rich areas
what is the secondary and tertiary structure of elastin
polypeptide chain form soluble tropoelastin molecules that can stretch and recoil
what is the quaternary structure of elastin
tropoelastin molecules aggregate to form large and insoluble elastin through interactions between the hydrophobic regions. this is stabilised throigh cross linking covalent bonds between lysine molecules. this gives flexibility so they can stretch and recoil without breaking
what would happen if our skin had no elastin
skin can stretch around our bones and muscles because of elastin. without elastin, skin would not go back to normal after being pinched. elastin in our lungs allows them to inflate and deflate and in out bladder it helps it expand to hold urine
what does collagen provide
mechanical strength in:
- in artery walls, a layer of collagen prevents the artery bursting when withstanding high pressure from blood being pumped by the heart
- tendons are made of collagen and connect muscles to bones, allowing them to pull on bones
- bones are made from collagen and reinforced with calcium phosphate making them hard
- cartilage and connective tissue are made from collagen
what is collagen made of
has a number of different forms but all are made up of 3 polypeptides wound together in a long and strong rope structure. it has flexibility.
what are some properties of collagen
- great tensile strength
- insoluble in water
- forms long straight fibres as it has a high proportion of hydrophobic amino acids
- flexible
why is collagen strong
its made from a small range of amino acids making three polypeptide chains tightly wound around in a rope-like structure. it has hydrogen bonds between chains and crosslinking covalent bonds between ropes and
the polypeptide chains overlap.
does collagen have a quaternary structure
there is little tertiary structure but 3 chains give it a quaternary structure
