Term
| list the 6 functions of proteins |
|
Definition
| Hormones, transport, structure, storage, Locomotion, Catalysis |
|
|
Term
|
Definition
| Peptides and proteins are made up of amino acids joined together by peptide bonds. |
|
|
Term
| What is the general structure of amino acids? |
|
Definition
H
|
NH2-C-COOH
|
R
The central carbon is referred to as the alpha carbon. |
|
|
Term
| Do most naturally occuring amino acids have D or L configuration? |
|
Definition
| Both D and L configuration occurs but most naturally occurring amino acids have L-configuration. |
|
|
Term
| List the general properties of amino acids. |
|
Definition
Colourless
Crystalline solids
High Melting poin and decompose on melting
Moderately soluble in water.
All the characteristics of ionic compounds. |
|
|
Term
|
Definition
A molecule or ion having separate positively and negatively charged groups.
Amino acids are amphoteric, they have both an acidic group (COOH) and a basic group (NH2) |
|
|
Term
| How are amino acids classified? |
|
Definition
| Amino acids are classified by the properties of their side chains. |
|
|
Term
|
Definition
Water "fearing"
non-polar side chain |
|
|
Term
|
Definition
water "loving"
polar, uncharged chains, negatively charged chains, positively charged chains. |
|
|
Term
|
Definition
| Amino acids can be linked together by an amide bond between the carboxylic group of one amino acid and the alpha-amino group of another amino acid. This link is called a peptide bond. |
|
|
Term
| Why is rotation around the peptide bond restricted? |
|
Definition
| Rotation about the peptide bond is restricted due to resonance. The peptide bond has some double bond character. |
|
|
Term
| List the 4 levels of protein structure. |
|
Definition
Primary structure: amino acid residues
Secondary structure: alpha-helix
Tertiary structure: Polypeptide chain
Quaternary structure: Assembled subunits |
|
|
Term
| Explain the primary structure of protein. |
|
Definition
Amino acid sequence and chain length/size (in daltons)
Involves the covalent peptide bonds in a protein.
The primary structure determines the physiological, structural and biological properties and functions of a protein.
ms: sickle cell anaemia |
|
|
Term
What does the 1˚structure determine?
Give an example |
|
Definition
The primary structure determines the physiological, structural and biological properties and functions of a protein.
MS: The 6th position in the normal ß chain of haemoglobin has glutamic acid, while a sickle ß chain has valine.
Blocked blood vessels can cause pain, serious infections and organ damage |
|
|
Term
| Explain the secondary structure of proteins. |
|
Definition
Seconday structure is the arrangement in spce of the atoms in the backbone of the protein.
The shape depends on the geometry of the peptide bond and local hydrogen bonding. |
|
|
Term
| Explain local hydrogen bonding. |
|
Definition
Local hydrogen bonding occurs between the amides in two peptide bonds.
The H on the N of the first amide, bonds with the carbonyl O of the amide.
/ \
O=C N-H
\ /
N-H...O=C
/ \ |
|
|
Term
| What are the two major types of secondary structure? |
|
Definition
Regular, repeating structure
Random coil/irregular structure. |
|
|
Term
| What properties does secondary structure bring to a protein? |
|
Definition
| Strength, insolubility, fibrous and flexibility. |
|
|
Term
| Explain the structure of the alpha helix. |
|
Definition
The helix is stabilised by hydrogen bonds formed between the amide hydrogen of one peptide bond and the carbonyl oxygen above it which is located in the next turn of the helix.
Side chain (R groups) are directed outwards. |
|
|
Term
| Explain the structure of ß-pleated sheets. |
|
Definition
Peptide chains adopt the conformation of a sheet of paper and the structure is stabilized by hydrogen bonds between peptide bonds.
Some of the strands are parallel and some are antiparallel depending on the relative direction of the peptide chains. |
|
|
Term
| Explain the tertiary structure of proteins. |
|
Definition
Further folding of the secondary structure gives overall 3 dimensional shape- involves side chain interaction.
Protein function is derived from the 3D structure (conformations) |
|
|
Term
|
Definition
| Covalent bonds between cysteine residues. |
|
|
Term
|
Definition
| attractions between R groups of non-polar amino acids. |
|
|
Term
|
Definition
| Interaction between polar amino acid R groups |
|
|
Term
|
Definition
| bonding between oppositely charged amino acid R groups. |
|
|
Term
| Name the 4 types of bonds involved in 3˚ structure of protein. |
|
Definition
| Disulphide crosslinks, hydrophobic attraction, hydrogen bonding, ionic bonding. |
|
|
Term
| Explain the quaternary structure of proteins. |
|
Definition
Many proteins are not single peptide strands but are combinations of several polypeptides.
These may exist as dimers, trimers, tetramers etc.
Subunits are usually identical |
|
|
Term
|
Definition
The pH of milk is 6.6
This is related to ß-lactoglobulin
ß-lactoglobulin acts as a dimer between pH5-pH8 |
|
|
Term
| ß-lactoglobulin acts as a .... between pH5-8 |
|
Definition
| ß-lactoglobulin acts as a dimer between pH5-8 |
|
|
Term
| ß-lactoglobulin acts as an .... between pH3-5 |
|
Definition
| ß-lactoglobulin acts as an octomer between pH3-5 |
|
|
Term
| ß-lactoglobulin acts as a .... above pH8 |
|
Definition
| ß-lactoglobulin acts as a monomer above pH8 |
|
|
Term
|
Definition
| water insoluble structural materials in animals. MS: keratins, collagens (cartilage & tendons). |
|
|
Term
| List the properties of fibrous proteins |
|
Definition
Primary structure is repetitive
They tend to lack chemically-reactive side groups. |
|
|
Term
| List 4 practical samples of fibrous proteins. |
|
Definition
| hair, feathers, wool, fur, horn, hoof, nail, shell, tendons, cartilage, skin |
|
|
Term
| List the general properties of alpha-Keratin |
|
Definition
It has a rope like structure based on the alpha helix which is cross-linked into bundles.
It can be very extensible
MS: wool fibres can be stretched to twice its length as hydrogen bonds between turns of the alpha-helix are broken. |
|
|
Term
| In hair alpha-helices are held together by what type of bonding? |
|
Definition
| In hair alpha-helices are held together by disulphide crosslinks. |
|
|
Term
| What bond helps to resist the stretch and to restore a stretched fibre to its original length? |
|
Definition
|
|
Term
The degree of S-S bridging determines ...?
|
|
Definition
| The degree of S-S bridging determines the properties of the keratin. |
|
|
Term
Soft keratin results in ... properties of keratin.
|
|
Definition
Soft keratins result in flexible, extensible properties and are low sulphur. MS: skin |
|
|
Term
| Hard keratins result in .... properties of the keratin. |
|
Definition
Hard keratins result in high sulphur properties in keratin. MS: horn (less flexible, less extensible) |
|
|
Term
| List the properties of collagen |
|
Definition
It is the most abundant protein in mammals. It is secreted by the cells of connective tissue. It is a major component of cartilage, skin, blood vessels and bone. It occurse in a triple helix form |
|
|
Term
|
Definition
| The three left-handed helix of the protein collagen. |
|
|
Term
| What properties does the tropocollagen bring to the collagen protein? |
|
Definition
| The triple helix tightens under tension, resisting stretching, making collagen inextensible. |
|
|
Term
| List the physical properties of the three strand keratin helix |
|
Definition
- It has a repetitive 1˚structure.
- It has bulky proline and hydroxyproline side chain rings.
- It has a tendency of chains to form left-handed helices spontaneously.
- Glycine at every third position sits in the interior of the helix where there is little space.
- Proline and Hydroxyproline R groups point outward.
|
|
|
Term
| The collective term for many collagen strands is... |
|
Definition
|
|
Term
| Fibres are stabilised by which two types of bonds? |
|
Definition
| These fibres are stabilised by extensice interchain hydrogen bonding and some covalent S-S cross-links. |
|
|
Term
| Three properties of collagen fibres are: |
|
Definition
- Stability
- Tensile strength
- Rigidity
|
|
|
Term
| Give an example of collagen fibres |
|
Definition
| Silk - extensible and very strong. |
|
|
Term
| List four functions of globular proteins. |
|
Definition
| Enzymes, hormones, transport, storage. |
|
|
Term
| Describe the characteristics of globular proteins. |
|
Definition
Globular proteins are water soluble, They are roughly spherical in shape, They are intricately folded so that hydrophobic side chains are tucked inside away from water, Examples are enzymes and hormones. |
|
|
Term
|
Definition
Myoglobin is the oxygen-holding protein in muscle tissue. |
|
|
Term
| Myoglobin is made from... |
|
Definition
Myoglobin consists of one polypeptide unit, of which 75% is an alpha-helix, with is further folded. Myoglobin also has a non-protein group (a prosthetic group) called a haem which holds the oxygen molecule. |
|
|
Term
| Haemoglobin is made from... |
|
Definition
1unit of haemoglobin is made up of 4 polypeptide molecules called globins. The globins are held together by electrostatic attraction and hydrogen bonds. |
|
|
Term
Haemoglobin has a... - primary structure?
- Secondary structure?
- Tertiary structure?
- Quaternary structure?
|
|
Definition
| Haemoglobin is made up of 4 globins therefore it has a quaternary structure. |
|
|
Term
| Globins are held together by _______ and _____. |
|
Definition
| Globins are held together by electrostatic attraction and hydrogen bonds. |
|
|
Term
In haemoglobin the haem groups carry what? In 1 unit of haemoglobin how many haem groups are there? |
|
Definition
| The 4 haem groups carry O2 and CO2 |
|
|
Term
|
Definition
Denaturation involves the disruption and possible distruction of both the secondayr and tertiary structures while peptide bonds remain. To destroy the characteristic properties by heat, acidity, or other effects that disrupt its molecular conformation. |
|
|
Term
| List the effects of denaturation. |
|
Definition
Disorganised protein will no longer act as intended. They will tend to clump together -coagulate/precipitate. |
|
|
Term
|
Definition
|
|
Term
| Is protein denaturation reversible? |
|
Definition
For a few small proteins, it is possible to find conditions that reverse denaturation (refolding). But it is irreversible for most proteins. |
|
|
Term
| Excessive heating of proteins can result in... |
|
Definition
|
|
Term
| Excessive heating of proteins in acid conditions can result in.... |
|
Definition
Hyrolyisis. Heating in acid conditions can result in the protein being reduced to simpler peptides and amino acids ie. breakage of peptide linkages. |
|
|
Term
| What is the effect of neutral/basic pH on proteins (in general!)? |
|
Definition
In nuetral/basic solution groups lose H: COOH --> COO- In basic amino acids the side chain charge changes with pH. |
|
|
Term
| What is the effect of neutral/acid pH on proteins? |
|
Definition
In neutral/acid solutions groups gain H: NH2 --> NH3+ In acid amino acids the side chain charge canges with pH |
|
|
Term
| What is the effect of neutral pH on proteins? |
|
Definition
Groups can either lose or gain H In neutral amino acids the side chain charge doesn't change with pH |
|
|
Term
| look at slide no. 67 amino acids, peptides and proteins. |
|
Definition
|
|
Term
| State the general rule of pKa |
|
Definition
If pH of a solution is less than the pKa, the H+ is on. If pH is higher than the pKa the H+ is off. |
|
|
Term
| What can we predict with the knowledge of pKa? |
|
Definition
| Knowing the pKa values of particular groups allows us to predict its form at particular pH's. |
|
|
Term
|
Definition
| yes. Proteins have a large number of potentially charged groups and demonstrate amphoteric properties similar to those of amino acids. |
|
|
Term
| Why do protein exhibit amphoteric properties? |
|
Definition
| Proteins have a large number of potentially charged groups and demonstrates amphoteric properties similar to those of amino acids. |
|
|
Term
| What overall effect will changing pH have on proteins? |
|
Definition
| Changing pH will alter the overall charge on protein which alters their solubility and possibly their shape. |
|
|
Term
| Define isoelectric point. |
|
Definition
The isoelectric point is the pH at which the total charge on the protein molecule is zero (no net electric charge) The isoelectric point varies between proteins. |
|
|
Term
| At a pH below the isoelectric point the protein will have what charge? |
|
Definition
| At pH below the isoelectric point it has a positive charge overall. |
|
|
Term
| At pH above the isoelectric point the protein will have what charge? |
|
Definition
| At pH above the isoelectric point it has a negative charge overall. |
|
|
Term
| What prevents aggregation in proteins? |
|
Definition
| Charged proteins repulse each other preventing aggregation. |
|
|
Term
| At what point to proteins tend to aggregate? |
|
Definition
| At the isoelectric point proteins tend to aggregate and are in their least soluble undenatured form. |
|
|
Term
| At what point are proteins at their least soluble, undenatured form? |
|
Definition
| At the isoelectric point. |
|
|
Term
| List three properties of proteins at the isoelectric point. |
|
Definition
- Proteins tend to aggregate.
- Proteins are in their least soluble form.
- Proteins are in their undenatured form.
|
|
|
Term
| What does electrophoresis do? |
|
Definition
| Electrophoresis is a method of separating positively charged proteins from negatively charged proteins. |
|
|
Term
| Name one type of complex protein. |
|
Definition
| Lipoproteins or glycoproteins. |
|
|
Term
|
Definition
Lipoprotein = protein + lipid. MS: toxins, blood, membrane & transport proteins, anitigens. |
|
|
Term
| List the properties of lipoproteins and give examples. |
|
Definition
Made from protein and lipid. May be covalently or non-covaelntly linked. Lipoproteins in the blood carry fats around the body. MS: toxins, blood, membrane proteins, transport proteins, antigens. |
|
|
Term
|
Definition
| Glycoprotein = proteins + carbohydrates. |
|
|
Term
List the properties of glycoproteins. give examples |
|
Definition
Made from proteins and carbohydrates. Usually proteins with oligosaccharides covalently attached. MS: antibodies, cell surface proteins (receptors), hormones. |
|
|
