amino acids and proteins

Question 1

what are proteins

Answer 1

• they are made up of carbon, hydrogen, nitrogen, oxygen and sometimes sulfur
• they are the building blocks of life
• there are millions of different proteins
• they are the most abundant molecule in cells
• they make up more than 50% of a cells dry mass

Question 2

what do proteins do

Answer 2

• enzymes
• carrier proteins transport molecules across the membrane
• antibodies defend against disease
• structural proteins support cells and tissues
• hormones transmit information
• transport proteins carry oxygen
• contractile proteins enable muscle contractions

Question 3

explain amino acids

Answer 3

• they have a central carbon atom
• they include a carboxylic acid group, an amino acid group, a hydrogen and a variable r group

Question 4

how do you join two amino acids

Answer 4

• they are joined by a condensation reaction
• the reaction involves the removal of a water molecule and the formation of a peptide bond

Question 5

what is a polypeptide chain

Answer 5

• a chain of amino acids can be build up
• the sequence and number of amino acids in the chain is determined by the DNA

Question 6

what are the 4 levels of protein structure

Answer 6

• primary
• secondary
• tertiary
• quaternary

Question 7

what is the primary structure of a protein

Answer 7

• the sequence of amino acids held together by peptide bonds
• controlled by the DNA

Question 8

what is the secondary structure of proteins

Answer 8

• the folding of the polypeptide chain
• it can coil into alpha helices
• it can fold into beta pleated sheets
• held together by peptide and hydrogen bonds

Question 9

what is the tertiary structure of a protein

Answer 9

• the further folding of the polypeptide chain to give a more complex 3d shape
• hydrogen bonds between polar r groups
• di-sulfide bonds between sulfur atoms in r groups
• ionic bonds between oppositely charged r groups
• hydrophobic and hydrophilic interactions between r groups

Question 10

what is the quaternary structure of proteins

Answer 10

• they are proteins that include more than one polypeptide chain
  eg - haemoglobin

Question 11

explain denaturing of proteins

Answer 11

• heating a protein increases the kinetic energy in the molecules
• this leads to the atoms vibrating
• causes the bonds holding the tertiary structure to break and reform which changes the shape of the active site in the protein

Question 12

what are globular proteins

Answer 12

• they are ball like structures
• hydrophobic r groups turn inwards towards the center of the amino acid
• more water soluble
• tend to have a metabolic role in living organisms

Question 13

what are fibrous proteins

Answer 13

• they form long fibres
• regular, repetitive sequence of amino acids
• usually insoluble in water
• tend to have structural roles in living organisms

Question 14

give examples of globular proteins

Answer 14

• enzymes
• channel proteins
• transport proteins
• hormones

Question 15

give examples of fibrous proteins

Answer 15

• structural proteins
• hair, skin, ligaments, tendons
• collagen and keratin

Question 16

what is the structure of haemoglobin

Answer 16

• has a quaternary structure
• 4 globin molecules held together by hydrogen bonds
• it also has a haem group
• compact
• soluble in water

Question 17

explain the structure of collagen

Answer 17

• three identical left handed helix polypeptide which form a triple helix
• the third amino acid is glycine
• chains held together by hydrogen bonds
• very stable and insoluble in water
• molecules cross link through covalent bonds which gives collagen great strength