amino acids Flashcards
what is a protein
a polymer of amino acids
what is the general formula for amino acids
NH2-CHR-COOH
what does the NH2 represent in an amino acids
the amine group
what does the R group represent in an amino acid
variable groups on amino acids
what does COOH represent in an amino acid
carboxyl group
what reaction occurs when you join 2 amino acids
condensation
how forms when you join 2 amino acids
dipeptide
what forms when you join many amino acids together
polypeptide
what bond is formed between amino acids
peptide bond
what are peptide bonds
covalent bonds and so involve the sharing of electrons
what happens during a hydrolysis reaction
the addition of water breaks the peptide bonds resulting in polypeptides being broken down into amino acids
what are the 4 levels of structure in proteins
primary
secondary
tertiary
quaternary
what is the primary structure
the sequence of amino acids bonded by covalent peptide bonds
the DNA of the cell determines the primary structure of a protein by instructing the cell to add certain amino acids in specific quantities in a certain sequences
the primary structure is specific for each protein (one alteration in the sequence of amino acids can affect the function of the protein)
what is the secondary structure
occurs when the weak negatively charged carboxyl group, CO-, interact with the weak positively charged amine group ,NH+, to form hydrogen bonds
there are two shapes that can form within proteins due to the hydrogen bonds
α-helix - occurs when the hydrogen bonds form between every fourth peptide bonds (between the oxygen of the carboxyl group and the hydrogen of the amine group)
β-pleated sheet - forms when the protein folds so that the two parts of the polypeptide chain and parallel to each other enabling hydrogen bonds to form between parallel peptide bonds
what is the tertiary structure
further conformational change of the secondary structure leads to additional bonds forming between the R groups
- hydrogen bonds between the R group
- disulphide - only occurs between cysteine amino acids
- ionic - occurs between charged R groups
- weak hydrophobic interactions - between non-polar R groups
what are disulphide bonds
strong covalent bonds that form between two cysteine R groups (only amino acid with a sulphur atom)
bonds are the strongest within a protein but occur less frequently and help stabilise the proteins
they are also know as disulphide bridges and are not broken down by high temperatures and pH changes
what are ionic bonds
form between oppositely charged R groups - holds different parts of the polypeptide chain together and contributes to the structure of proteins
ionic bonds are stronger than hydrogen bonds
broken by pH changes - denature of enzymes
what are hydrogen bonds
form between strongly polar R groups
these are the weakest bonds that form but are the most common as they form between a wide variety of R groups
broken by high temp and pH changes
what are hydrophobic and hydrophilic interactions
several amino acids have uncharged R groups - Non-polar amino acids. they are not attracted to water = hydrophobic and tend to cluster together at the centre of the protein to exclude water molecules = HYDROPHOBIC INTERACTIONS
HYDROPHILIC amino acids tend to be found of the surface of proteins where they can interact with water molecules
HYDROPHOBIC & HYDROPHILIC interactions are relatively weak bonds
how does the tertiary structure determine the function of a protein
a polypeptide chain will fold differently due to the interactions between the R groups
each of the twenty amino acids that make up proteins has a unique group and therefore many different interactions can occur creating a range of proteins and functions
what is the quaternary structure
exists in proteins that have more than one polypeptide chain working together as a functional macromolecule e.g. haemoglobin
each polypeptide chain in the quaternary structure is referred to as a subunit of the protein
globular proteins
molecules of a relatively spherical shape, which are soluble in water and often have metabolic roles within the organisms
fibrous proteins
has a relatively long, thin rope-like molecules that are insoluble in water and metabolically inactive, often having a structural role with an organism e.g. in bones or tendons or in the walls of blood vessels such as arteries
what is elastin
the skin contains a large amount of elastin fibres which help to make the skin supple and elastic. elastin is also found in the walls of arteries
elastin fibres stretch when blood pulses through the artery and then recoils in between pulses helping the artery to return to its normal shape
elastin molecules are long strands containing hydrophobic regions and strands are cross linked to each other
