save my exams proteins Flashcards
why proteins are important
-Enzymes
-Cell membrane proteins (eg. carrier)
-Hormones
-Immunoproteins (eg. immunoglobulins)
-Transport proteins (eg. haemoglobin)
-Structural proteins (eg. keratin, collagen)
-Contractile proteins (eg. myosin)
amino acids
monomers of proteins
An amine group -NH2
A carboxylic acid group -COOH
A hydrogen atom
An R group
peptide bonds
-a hydroxyl (-OH) is lost from the carboxylic group of one amino acid and a hydrogen atom is lost from the amine group of another amino acid
-remaining carbon atom from the first amino acid bonds to the nitrogen atom of the second amino acid
-This is a condensation reaction so water is released
how polypeptide bonds are broken
hydrolysis reactions, the addition of water breaks the peptide bonds resulting in polypeptides being broken down to amino acids
how many protein structures
4
primary structure
-The sequence of amino acids bonded by covalent peptide bonds
-specific for each protein
-DNA of a cell determines the primary structure of a protein
-affects the shape and therefore the function of the protein
secondary structures
-occurs when the weak negatively charged nitrogen and oxygen atoms interact with the weak positively charged hydrogen atoms to form hydrogen bonds
-α-helix
-β-pleated sheet
-only relates to hydrogen bonds forming between the amino group and the carboxyl group
how hydrogen bonds are broken
high temperatures and pH changes
alpha helix
occurs when the hydrogen bonds form between every fourth peptide bond
beta pleated sheets
forms when the protein folds so that two parts of the polypeptide chain are parallel to each other enabling hydrogen bonds to form between parallel peptide bonds
what proteins have a secondary structures
collagen and keratin
tertiary structure
-conformational change of the secondary structure leads to additional bonds forming between the R groups
-hydrogen
-disulphide
-ionic
-3d
what protein has tertiary structure
globular
quaternary structure
Occurs in proteins that have more than one polypeptide chain working together as a functional macromolecule, for example, haemoglobin
Each polypeptide chain in the quaternary structure is referred to as a subunit of the protein
disulphide
strong covalent bonds
Can be broken by reduction
Disulfide bonds are common in proteins secreted from cells eg. insulin
ionic
form between positively charged (amine group -NH3+) and negatively charged (carboxylic acid -COO-) R groups
stronger than hydrogen bonds
broken by pH changes
hydrogen
form between strongly polar R groups. These are the weakest bonds that form but the most common as they form between a wide variety of R groups
hydrophobic
form between the non-polar (hydrophobic) R groups within the interior of proteins
globular protein
compact
spherical
soluble in water
The solubility of globular proteins in water mean can be easily transported around organisms and be involved in metabolic reactions
folding of the protein due to the interactions between the R groups results in globular proteins having specific shapes.
enzymes can catalyse specific reactions and immunoglobulins can respond to specific antigens
conjugated proteins that contain a prosthetic group eg. haemoglobin which contains the prosthetic group called haem
fibrous proteins
-long strands of polypeptide chains that have cross-linkages due to hydrogen bonds
-large number of hydrophobic R groups fibrous proteins are insoluble in water
- repetitive sequence
-organised structures that are strong and this along with their insolubility property
-suitable for structural roles, for example, keratin that makes up hair, nails
-collagen which is a connective tissue found in skin, tendons and ligaments
structure of haemoglobin
-globular protein
-quaternary structure as there are four polypeptide chains.
-prosthetic haem group
-hydrophobic R groups are facing inwards
-hydrophilic R groups
-prosthetic haem group contains an iron
-combine with an oxygen molecule forming oxyhaemoglobin
-Each haemoglobin with the four haem groups can therefore carry four oxygen molecules (eight oxygen atoms)
function of haemoglobin
responsible for binding oxygen in the lung and transporting the oxygen to tissue
oxygen is not very soluble in water and haemoglobin is, oxygen can be carried more efficiently around the body when bound to the haemoglobin
collagen structure
three polypeptide chains closely held together by hydrogen bonds to form a triple helix
Covalent bonds also form cross-links between R groups of amino acids in interacting triple helices when they are arranged parallel to each other
many fibrils are arranged together they form collagen fibres
Collagen fibres are positioned so that they are lined up with the forces they are withstanding
collagen function
Flexible structural protein forming connective tissues
many hydrogen bonds within the triple helix structure of collagen results in great tensile strength
withstand large pulling forces without stretching or breaking
staggered ends ibrils provide strength
