Structure of Proteins Flashcards
Define a protein.
- Highly complex substance that is present isn all living organism
- Required for the structure, function and regulation of the body’s tissues and organs
State the functions of proteins.
- Enzymes: catalyse chemical reactions in cells - speed up reactions that would be too slow to sustain life
- Structural support: collagen provides structural support for tissue, such as skin and bones
- Hormones: insulin regulate various physiological processes in the body such as blood sugar levels
- Cell signalling: involved in transmitting signals within and between cells, regulating processes like cell growth and differentiation
What are proteins made up of?
They are polymers of amino acids
Describe the structure of amino acids.
Contain both an amine (alkali group) and a carboxylic acids (acidic group)
Describe the reaction of amino acids.
- Acids react with amines to produce salts
- In neutral pH amino acids react with themselves producing a zwitterion
What is a zwitterion?
- A double ion or two charges on the same molecule
When does a cation (+) form?
At low pH
When does an anion (-) form?
At high pH
How do dimers, trimers form?
- When amino acids react with other amino acids
- Form by producing a new chemical bond called an amide bond or a peptide bond
What enzyme is involved in the formation of a peptide bond between amino acids?
Peptidyl transferases
What is a peptide?
Two or more amino acids joined together by peptide bonds
What is a polypeptide?
A chain of many amino acids
Describe protein structure.
Primary structure - a linear chain of amino acids in a polypeptide chain
Secondary structure: folded structures that from within a polypeptide due to interaction between atoms of the backbone
Tertiary structure: 3D structure of a polypeptide - formed due to interactions between the R groups of the amino acids in the protein
Quaternary structure: multiple polypeptide chains
Which bond is involved in the secondary structure?
Hydrogen bonds
What are the two main types of arrangement of the secondary structure?
- Alpha helix
- Beta pleated sheets
Describe the alpha helix structure.
- A narrow tube, coiled in a right hand spiral
- Hydrogen bonds between the C=O of one peptide and the N-H of another peptide group 4 units ahead in the primary structure
- Hydrogen bonds run in parallel to the helix, within one polypeptide chain
to stabilised the protein structure
Describe beta pleated sheets.
- Two or more lengths of the polypeptide chains lie in parallel to each other
- R groups of the amino acids above and below the sheets, while the NH and C=O parts of the peptide bond point towards each other
- Hydrogen bonds between these sections
- The backbone of the polypeptide chain is extended into a zigzag rather than
helical structure
Which bonds are involved in the tertiary structure?
Disulfide bonds, peptide bonds, covalent bonds, hydrogen bonds and van der Waals forces
Where are disulphide bonds primarily found?
In secreted, extracellular proteins, e.g. hormone, insulin
State the role of metal ions in the formation of the tertiary structure.
- Assists in the folding and stabilising of protein structure i.e. calcium in calmodulin protein
Describe the role of calmodulin.
- A multifunctional intermediate calcium-binding messenger protein
- The structure changes with the addition of calcium
- This change occurs with rotation and bonding with the calcium
What bonds are involved in the quaternary structure?
same as tertiary structure
State the two categories of proteins in the quaternary structure.
Fibrous and globular
Define proteolysis.
Polypeptide chain is cleaved into fragments which take on different shapes
Define glycosylation.
The addition of sugars to polypeptide chains - is important in targeting and recognition
Define phosphorylation.
The addition of phosphate groups
- often changes the shape of the protein, exposing an active site of an enzyme or binding site for another molecule
What is insulin and where is it produced?
- A peptide hormone
- Produced in the beta cells of the pancreas
What does insulin regulate?
- The metabolism of carbohydrates, fats and proteins
What does insulin promote?
- Absorption of glucose from the blood into liver, fat and skeletal muscle cells
What does a decrease of insulin activity result in?
- Diabetes mellitus - a condition of high blood sugar level (hyperglycaemia)
Why is insulin administered via injection?
- It is too big to pass through the phospholipid bilayer of the gastrointestinal cell
- Would be digested by enzymes in the gastrointestinal tract
How does folding affect insulin activity?
- Folding pattern allows the protein to bind to the receptor adequately to initiate the reaction (makes insulin more stable)
How does hydration affect insulin activity.
- Affects solubility and folding
- If water molecules are attached certain fat soluble hydrophobic amino acids will move away from these water molecules; this affects folding and the 3D structure
- Hydrophobic amino acid side chains tend to cluster in a protein’s interior, away from water
- When the protein is folded, these clusters form a hydrophobic protein core
Why can’t we dry protein such as insulin?
All the associated water molecules will be removed which will alter the folding pattern of the protein which cannot be rectified by rehydration - it is impossible to weigh insulin and other therapeutic proteins
How are therapeutic proteins quantified?
- Pharmacological testing
- We measure how much the glucose level in the rabbit has reduced with our injection
How is insulin harvested?
human DNA is injected into bacteria or other living organisms - recombinant DNA technology
