1.3 (biological molecules) Flashcards
proteins
proteins are polymers (and macromolecules) made of monomers called
amino acids
the sequence, type and number of the amino acids within a protein determines its shape and therefore its
function
proteins are extremely important in cells because they form all of the following:
- enzymes
- cell membrane proteins (eg. carrier)
- hormones
- immunoproteins (eg. immunoglobulins)
- transport proteins (eg. haemoglobin)
- structural proteins (eg. keratin, collagen)
- contractile proteins (eg. myosin)
there are how many amino acids found in proteins common to all living organisms
20
the general structure of all amino acids is a central carbon atom bonded to:
- an amine group: NH2
- a carboxylic acid group: COOH
- a hydrogen atom
- an R group (which is how each amino acid differs and why amino acid properties differ e.g. whether they are acidic or basic or whether they are polar or non-polar)
in order to form a peptide bond 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
during the formation of a peptide bond the remaining carbon atom (with the double-bonded oxygen) from the first amino acid bonds to
the nitrogen atom of the second amino acid
the formation of a peptide bond is a condensation reaction so water is
released
dipeptides are formed by the condensation of
two amino acids
polypeptides are formed by the condensation of
many (3 or more) amino acids
during hydrolysis reactions of polypeptidds, the addition of water breaks
- the peptide bonds
- resulting in polypeptides being broken down to amino acids
amino acids are bonded together by covalent peptide bonds to form a dipeptide in a condensation reaction diagram
what are the four levels of structure in proteins
- primary
- secondary
- tertiary
- quaternary
three of the four levels of the structure in proteins are related to a single polypeptide chain and the fourth level relates to a protein that has
two or more polypeptide chains
the sequence of amino acids bonded by covalent peptide bonds is the
primary structure of a protein
primary structure of a protein is the sequence of
amino acids bonded by covalent peptide bonds
DNA of a cell determines which structure of a protein
primary structure
DNA of a cell determines the primary structure of a protein by instructing the cell to
- add certain amino acids in specific quantities
- in a certain sequence
DNA of a cell determines the primary structure of a protein by instructing the cell to add certain amino acids in specific quantities in a certain sequence, this affects the
shape and therefore the function of the protein
the primary structure is what for each protein
- specific
- (one alteration in the sequence of amino acids can affect the function of the protein)
the primary structure of a protein diagram
the three-letter abbreviations indicate the specific amino acid (there are 20 commonly found in cells of living organisms)
the secondary structure of a protein occurs when
the weak negatively charged nitrogen and oxygen atoms interact with the weak positively charged hydrogen atoms
the secondary structure of a protein occurs when the weak negatively charged nitrogen and oxygen atoms interact with the weak positively charged hydrogen atoms to form
hydrogen bonds
what are the bonds in the secondary structure of proteins
hydrogen
there are two shapes that can form within proteins due to the hydrogen bonds:
- α-helix
- β-pleated sheet
the α-helix shape occurs when the hydrogen bonds form between every
- fourth peptide bond - (between the oxygen of the carboxyl group and the hydrogen of the amine group)
the β-pleated sheet shape forms when the protein
folds
the β-pleated sheet shape forms when the protein folds so that
two parts of the polypeptide chain are parallel to each other
the β-pleated sheet shape 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
most fibrous proteins have which protein structures
- secondary structures - (e.g. collagen and keratin)
the secondary structure only relates to hydrogen bonds forming between which two groups
- amino group
- carboxyl group (the ‘protein backbone’)
the hydrogen bonds in the secondary structure can be broken by what two things
- high temperatures
- pH changes
the secondary structure of a protein with the α-helix and β-pleated sheet shapes highlighted diagram
the magnified regions illustrate how the hydrogen bonds form between the peptide bonds
further conformational change of the secondary structure leads to additional bonds forming between the
R groups (side chains)
in the tertiary structure the additional bonds between the R groups (side chains) are
- hydrogen (these are between R groups)
- isulphide (only occurs between cysteine amino acids)
- ionic (occurs between charged R groups)
- weak hydrophobic interactions (between non-polar R groups)
the tertiary structure is common in what proteins
globular proteins
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 what of the protein
subunit
peptide bonds occure in which level
- primary
- secondary
- tertiary
hydrogen bonds occur in which levels
- secondary (only between the amino and carboxyl groups)
- tertiary (R groups + amino and carboxyl groups)
disulphide bonds occur in which level
tertiary
ionic bonds occur in which level
tertiary
hydrophobic interactions occur in which level
tertiary
remember that the hydrogen bonds in tertiary structures are between the R groups whereas in secondary structures the hydrogen bonds form between the
amino and carboxyl groups
polypeptide chain will fold differently due to the
- interactions (and hence the bonds that form)
- between R groups
each of the twenty amino acids that make up proteins has a unique
R group
each of the twenty amino acids that make up proteins has a unique R group and therefore many different
- interactions can occur
- creating a vast range of protein configurations
- and therefore functions
within tertiary structured proteins are the following bonds
- strong covalent disulfide
- weak hydrophobic interactions
- weak hydrogen
- ionic
disulfide bonds are strong
- covalent bonds
- that form between two cysteine R groups (as this is the only amino acid with an available sulfur atom in its R group)
strong covalent disulfide bonds are the strongest within a protein, but occur less frequently, and help
- stabilise the proteins
- disulfide bridges
disulfide bridges can be broken by
reduction
disulfide bonds are common in proteins that are what from cells
- secreted
- eg. insulin
ionic bonds form between
- positively charged (amine group -NH3+)
- and negatively charged (carboxylic acid -COO-) R groups
ionic bonds are stronger than hydrogen bonds but they are not
common
ionic bonds are broken by
pH changes
hydrogen bonds form between
strongly polar R groups
hydrogen are the weakest bonds that form but the most common as they form between a wide variety of
R groups
hydrophobic interactions form between
- non-polar (hydrophobic) R groups
- within the interior of proteins
globular proteins are
- compact
- roughly spherical (circular) in shape
- soluble in water
globular proteins form a spherical shape when folding into their tertiary structure because
- their non-polar hydrophobic R groups are orientated towards the centre of the protein away from the aqueous surroundings and
- their polar hydrophilic R groups orientate themselves on the outside of the protein
this orientation enables globular proteins to be what in water
sluble
this orientation enables globular proteins to be (generally) soluble in water as the water molecules can
surround the polar hydrophilic R groups
the solubility of globular proteins in water means they play important physiological roles as they can be easily
transported around organisms
the solubility of globular proteins in water means they play important physiological roles as they can be easily transported around organisms and be involved in
metabolic reactions
the folding of the protein due to the interactions between the R groups results in globular proteins having
specific shapes
the folding of the protein in globular proteins enables them to play physiological roles, for example, enzymes can
catalyse specific reactions
the folding of the protein in globular proteins enables them to play physiological roles, for example, enzymes can catalyse specific reactions and immunoglobulins can
respond to specific antigens
some globular proteins are conjugated proteins that contain a
a prosthetic group eg. haemoglobin which contains the prosthetic group called haem
fibrous proteins are long strands of
- polypeptide chains
- that have cross-linkages due to hydrogen bonds
fibrous proteins have little or no
tertiary structure
due to the large number of hydrophobic R groups fibrous proteins are
insoluble in water
fibrous proteins have a limited number of
amino acids with the sequence usually being highly repetitive
the highly repetitive sequence creates very organised structures that are strong and this along with their insolubility property, makes fibrous proteins very suitable for
- structural roles
- for example, keratin that makes up hair, nails, horns and feathers and collagen which is a connective tissue found in skin, tendons and ligaments
what is the shape of glodbular proteins
roughly circular
what is the shape of fibrous proteins
long strands
what is the amino acid sequence of globular proteins
- irregular
- wide range of R groups
what is the amino acid sequence of fibrous proteins
- repetitive
- limited range of R groups
function of globular proteins
- physiological
- functional
function of fibrous preoteins
structural
examples of globular proteins
- haemogoblin
- enzymes
- insulin
- immunogoblin
examples of fibrous proteins
- collagen
- keratin
- myosin
- actin
- fibrin
solubility of globular proteins
generally soluble in water
solubility of fibrous proteins
generally insoluble in water
to distinguish between the two proteins, learn SAFES
(Shape, Amino acid sequence, Function, Examples and Solubility)
