Amino Acids & Proteins Flashcards
How many naturally occuring amino acids are there?
20.
Amino acids are joined together in what type of chains to form proteins?
Polypeptide chains.
How long are the polypeptide chains that form proteins?
From a few hundred to over a thousand amino acids long.
Every amino acid has the same structure, except for…?
The R group.
What part of a protein is involved in reactions with a substrate?
The R group.
If the R group is changed, what effect can this have on a protein?
It can destroy the protein.
What FOUR atoms or groups are attached to the central carbon atom of an amino acid?
- A hydrogen atom.
- A carboxyl group (COOH).
- An amino group (NH2).
- An R group.
Of the carboxyl group and amino group in an amino acid, which is an organic acid and which is an organic base?
Organic acid - carboxyl group.
Organic base - amino group.
What are the three groups of amino acids?
- Non-polar side chains and hydrophobic.
- Polar with uncharged side chains.
- Polar with charged (acidic or basic) side chains.
Which group of amino acids is this?:
Alanine, valine, leucine, isoleucine, glycine, proline, methionine, phenylalanine and tryptophan.
Non-polar side chains and hydrophobic.
Which two amino acids are aromatics, with ring structures that can be involved in fluorescence?
Phenylalanine and tryptophan.
What type of bond joins individual amino acids to form proteins?
Peptide bonds.
Methionine contains sulphur. This means that it can be involved in what sort of bonding?
Metal bonding.
Which group do these amino acids belong to?:
Serine, threonine, cysteine, tyrosine, asparagnine, glutamine and histidine.
Polar with uncharged side chains.
Which group do these four amino acids belong to?:
Aspartate, glutamate, lysine, and arginine.
Polar side chains (charged, either acidic or basic).
Name the nine essential amino acids.
Phenylalanine, tryptophan, isoleucine, valine, methionine, lysine, threonine, leucine and histidine.
Why are the nine essential amino acids so-called?
They are essential for physiological functions but cannot be synthesised by humans.
Kwashiorkor is a condition caused by a diet adequate in ………………. but lacking ……………… .
Carbohydrates, amino acids.
All amino acids have chiral centres and are optically active, but are they all R-enantionmers or L-enantiomers?
Amino acids are all L-enantiomers.
Are only R-enantiomers or L-enantionmers of amino acids used to make proteins?
Only L-enantiomers of amino acids are used to make proteins.
Give an example of why chirality can be important.
Chirality is very important in drug design. For example, the R-enantiomer of prozac is effective, but the L-enantiomer is dangerous.
Amino acids are important physiological buffers. What is the function of a buffer?
Buffers are solutions that resist changes in pH upon addition of an acid or a base, keeping enzymatic reactions at a constant pH.
What do buffers take up or release in order to maintain enzymatic reactions at a constant pH?
H+ ions.
If a solution has a high pH, does it have a lot of H+ ions or very few pH ions in solution?
It has very few H+ ions in solution so it is very basic.
Solutions with a low pH have ………………. H+ ions in solution.
Solutions with a low pH have lots of H+ ions in solution and they are very acidic.
Are amino acids weak acids or strong acids?
Weak acids.
How many titratable protons do amino acids possess?
At least two.
What sort of reaction forms peptide bonds? What is released in the reaction?
Peptide bonds are formed in condensation reactions and a molecule of water is released.
Peptide bonds are ………… bonds, which restricts …………….. of the polypeptide chain.
Double, rotation.
True or false? Proteins can only fold where there is a single bond in the polypeptide chain.
True. Proteins can only fold where there is a single bond because double bonds restrict rotation of the chain.
Polypeptide chains can be ……………….. (2D) when a carbon has ………………. binding atoms?
Planar, three.
Can polypeptide chains be cis or trans?
Yes, in a planar conformation polypeptide chains can be cis or trans.
What is the difference between a cis polypeptide chain and a trans polypeptide chain?
Cis polypeptide chains have the R groups on the same side.
Trans polypeptide chains have R groups on opposite sides.
What is a potential problem with cis polypeptide chains?
There can be problems with cis polypeptide chains when the amino acids are large or polar.
There can be short peptides as well as polypeptide chains. What function do these short peptides often have in the body?
Short peptides are often used in signalling, where their structure is not very important. Many hormones are short peptides.
What are the two forms that polypeptides can fold into to form a secondary structure?
Alpha helices and beta pleated sheets.
What type of bonds hold alpha helices and beta pleated sheets together?
Hydrogen bonds.
Name some of the forces involved in protein folding.
Hint: there are five main forces.
Hydrophobic interactions, hydrogen bonds, electrostatic attraction, metal ion coordination and covalent bridges (e.g. disulfide bridges).
True or false? The three-dimensional shape of a protein has no impact on its function.
False. A protein’s 3D shape is critical to it’s function.
Does the primary structure of a protein have any influence on its secondary or tertiary structure?
Yes, the primary structure of a protein dictates its secondary and tertiary structures.
As a general rule in biochemistry, when a molecule is produced in several steps, how is overproduction of the end product often prevented?
Usually accumulation of the end product inhibits the first step of production, thus preventing overproduction.
If a protein is water soluble, it will fold into compact structures - will the core be polar or non-polar?
Polar.
If proteins are identified as follows, what are they being classified by? What does this depend on?:
Structural proteins, enzymes, transport and storage, muscle contraction and mobility, protection, regulation and receptors.
Biological role. This all depends on a protein’s structure.
