globular and fibrous proteins

what are globular proteins?

soluble proteins with a specific 3D shape

examples of globular proteins

antibodies, hormones, enzymes, hemoglobin

Why do globular proteins form a spherical shape?

- non-polar hydrophobic R groups are orientated towards the centre of the protein away from the aqueous surroundings

- polar hydrophilic R groups orientate themselves on the outside of the protein

what is haemoglobin made of?

Four peptide chains, each with 4 iron-containing haem prosthetic groups

Haemoglobin structure

- globular

- four polypeptide chains

- Each chain is called "globin"

- Each chain contains a haem prosthetic group that has an iron atom

what two types of chains are present in haemoglobin?

alpha globin and beta globin. there are 2 of each

how much oxygen can one prosthetic group carry?

one molecule

how much oxygen can haemoglobin carry?

Each Haemoglobin can carry four oxygen molecules.

what makes blood red?

iron in hemoglobin

what happens when oxygen combines with haemoglobin?

a molecule called haemoglobin is formed, which is bright red in colour

what colour is blood when there is no oxygen?

a dark red

fibrous protein structure

long protein strands composed of mostly non polar amino acids

what is the most common protein found is animals?

collagen

where is collagen found?

- tendons

- skin

- cartilage

- bone and teeth

- blood vessels

collagen structure

three polypeptide chains held in a tight helix structure

what are the chains that form the triple helix in fibrous proteins held together by?

hydrogen and covalent bonds

how do the chains in collagen stay close together?

every third amino acid in the polypeptide chains is glycine, the smallest amino acid

what is glycine?

amino acid

what is the function of glycine?

inhibitory interneurons

where is glycine found?

spinal cord and brain stem

how are fibrils formed?

-the triple helixes lie parallel to each other and form covalent bonds between the R groups

what is smallest amino acid?

Glycine

What are conjugated proteins?

Globular proteins that contain a non-protein component are called a prosthetic group.

what carries oxygen in the haemoglobin?

The Haem R group( Fe 2+) that binds to oxygen( O2-)

features of collagen

- triple helix

- most prominently found protein

- structural role

- not soluble

is collagen soluble?

No, it's insoluble

3 multiple choice options

are the polypeptide chains found in collagen loose pr tightly held together?

they are tightly held together

why do the triple helices in collagen lie in parallel?

they interact with each other due to hydrogen bonds, leading to increased strength

collagen in tendons features

- form parallel bundles of fibrils lined up in the direction of tension

- high tensile strength

why do tendons have high tensile strength?

collagen fibrils are made from lots of collagen that are held tightly together, making them very flexible without permanent damage

How is collagen arranged in skin?

Individual fibres are cross-woven into sheets that can be stretched

features of collagen in skin

- overlap in all directions

why does skin collagen overlap in all directions?

it needs to be strong in all directions, allowing it to resist tensile forces from all directions

what is the most common protein?

collagen

dipeptide structure

Two amino acids bonded together through a condensation reaction, forming water as a subproduct

what do most fibrous proteins have?

secondary secondary structures

beta pleated sheet structure

alpha helix structure

where are tertiary structures more common in?

globular proteins

what type of bonds are there in antibodies?

disulfide

what is more common: ionic bonds or hydrogen bonds?

ionic

which bond is stronger: hydrogen of ionic?

ionic

what breaks ionic bonds?

-pH changes

-salt changes

why is it important for globular proteins to be soluble?

- can be easily transported

- play an important role in physiological metabolic reactions

How does sickle cell anemia occur?

The hb beta subunit contains a mutation. Glutamate at #6 (hydrophilic) is mutated to valine (hydrophobic). Changes Hb crystallization in RBC and becomes rigid. in other words, the centre becomes hydrophobic and the outside becomes hydrophilic

how is haemoglobin adapted for its function?

- Haemoglobin forms long, flexible fibres that increase the elasticity of red blood cells.

- Hemoglobin has a globular structure that can bind to oxygen molecules in the quaternary structure and transport them around the body

Where is trypsin produced?

Pancreas and small intestine

where is trypsin found?

small intestine(duodenum)

silk structure

Beta pleated sheet with interlocking Ala and Gly residues

haemoglobin function

*transports oxygen and carbon dioxide

*carry oxygen and carbon dioxide back to the lungs

*transport oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs

how does oxygen alter the haemoglobin?

- O molecule binds to haemoglobin, alters the quaternary structure(due to tertiary being altered)

- haemoglobin has a higher affinity for subsequent O molecules and binds easier

what does the existence of Fe allow for?

Fe 2+ allows for oxygen to bind reversibly

How does the tertiary structure enable haemoglobin to perform its role in transporting oxygen?

the hydrogen bonds ensure that the outside has hydrophilic R groups so it is soluble

How does the quaternary structure enable haemoglobin to perform its role in transporting oxygen?

- have to contain haem groups so they can bind to oxygen

- 4 polypeptide chains that bond to 4 oxygen molecules

what part of fibrous proteins is insoluble?

the R prosthetic groups in large numbers make them insoluble

do fibrous proteins frequently have tertiary structures?

no, there are either very few or none

how do fibrous proteins have an organised structure?

- limited number of amino acids with a repetitive sequence

- this makes them very strong and organised

what amino acids are the most common in cellulose?

- glycine

- proline

- hydroxyproline

what bonds are present in cellulose?

- beta 1,4 glycosidic bonds

- hydrogen

- covalent

what is the function of covalent bonds in cellulose?

- they form crosslinks between R groups of amino acids in interacting triple helices when arranged parallel

- the cross-links hold the collagen molecules together, forming fibrils

how are collagen fibrils arranged?

they are positioned so that they can line up with the forces that are withstanding

why is collagen stable?

due to the high proportion of proline and hydroxyproline amino acids, causing their R groups to repel each other, providing more stability

why is collagen insoluble? why is it important?

- long, tightly packed structure

- collagen has many hydrophobic regions

- collagen needs to remain insoluble to support tissues

- insolubility helps form strong extracellular matrices in tissues

why are the staggered ends of collagen important?

- creates a strong interlacing structure

- distributes force more evenly, making them resistant to tension and mechanical tissues

- provides strength and flexibility

how do the R groups of collagen form a ring structure?

the r groups(side chains) of the amino acids are cyclic, forming a ring structure, causing the restriction of movement in the polypeptide chain, making them more rigid

How is triple helix of collagen stabilized?

H bonds between hydroxyproline and other collagen molecules

collagen vs haemoglobin

why is collagen tertiary and not quaternary?

- more than one polypeptide chain(3)

- triple helix