save my exams proteins

Question 1

why proteins are important

Answer 1

-Enzymes
-Cell membrane proteins (eg. carrier)
-Hormones
-Immunoproteins (eg. immunoglobulins)
-Transport proteins (eg. haemoglobin)
-Structural proteins (eg. keratin, collagen)
-Contractile proteins (eg. myosin)

Question 2

amino acids

Answer 2

monomers of proteins
An amine group -NH2
A carboxylic acid group -COOH
A hydrogen atom
An R group

Question 3

peptide bonds

Answer 3

-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

Question 4

how polypeptide bonds are broken

Answer 4

hydrolysis reactions, the addition of water breaks the peptide bonds resulting in polypeptides being broken down to amino acids

Question 5

how many protein structures

Answer 5

4

Question 6

primary structure

Answer 6

-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

Question 7

secondary structures

Answer 7

-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

Question 8

how hydrogen bonds are broken

Answer 8

high temperatures and pH changes

Question 9

alpha helix

Answer 9

occurs when the hydrogen bonds form between every fourth peptide bond

Question 10

beta pleated sheets

Answer 10

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

Question 11

what proteins have a secondary structures

Answer 11

collagen and keratin

Question 12

tertiary structure

Answer 12

-conformational change of the secondary structure leads to additional bonds forming between the R groups
-hydrogen
-disulphide
-ionic
-3d

Question 13

what protein has tertiary structure

Answer 13

globular

Question 14

quaternary structure

Answer 14

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

Question 15

disulphide

Answer 15

strong covalent bonds
Can be broken by reduction
Disulfide bonds are common in proteins secreted from cells eg. insulin

Question 16

ionic

Answer 16

form between positively charged (amine group -NH3+) and negatively charged (carboxylic acid -COO-) R groups
stronger than hydrogen bonds
broken by pH changes

Question 17

hydrogen

Answer 17

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

Question 18

hydrophobic

Answer 18

form between the non-polar (hydrophobic) R groups within the interior of proteins

Question 19

globular protein

Answer 19

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

Question 20

fibrous proteins

Answer 20

-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

Question 21

structure of haemoglobin

Answer 21

-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)

Question 22

function of haemoglobin

Answer 22

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

Question 23

collagen structure

Answer 23

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

Question 24

collagen function

Answer 24

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