Biochem, proteins, amino acids Flashcards
Draw the structure of an amino acid
[drawing]
What are the two functional groups called on an amino acid?
primary amino group, carboxylic acid group
What is the position called that is adjacent to the carboxylic acid group?
alpha position
How many naturally occurring amino acids are there?
about 20
What is the range of amino acids that some people argue?
18-22
The majority of amino acids exhibit optical isomerism as they have…
chiral carbons
What amino acid does not have a chiral carbon?
glycine
What happens in nature in the production of amino acids?
only one enantiomer is made - only one form in the body
What happens in the lab in the production of amino acids?
a racemic mixture, 50:50 mixture of both enantiomers so are optically inactive
Discuss the properties of amino acids
-have both acidic and basic properties
-classed as amphoteric
Why are amino acids amphoteric?
contain:
-carboxylic acid group that is acidic - donate protons
-amino group that is basic - accept protons
What is the equation for amino acids acting as an acid/donating protons?
RCH(NH2)COOH + OH- –>
RCH(NH2)COO- + H2O
What is the equation for amino acids acting as a base/accepting protons?
RCH(NH2)COOH + H+ –>
RCH(N+H3)COOH + H2O
At room temperature, what state are amino acids?
white crystalline solids
Name some other properties of amino acids?
dissolve in water and have high melting points
Why do amino acids have such high melting points?
-NOT because of hydrogen bonding
-because amino acids exist as zwitterions, which have ionic bonding (stronger than hydrogen bonding)
What is a zwitterion?
an ion that has both a positively charged and a negatively charged group
In strong alkali, what happens to a zwitterion?
COO- zwitterion loses a proton/acts as an acid
In strong acid, what happens to a zwitterion?
N+H3 zwitterion accepts protons/acts as a base
How does the zwitterion behave in acid/alkaline conditions?
as a buffer
How do amino acids join together to form peptides?
by peptide links
What type of polymerisation do amino acids undergo?
condensation - water is formed as well as the peptide
How many different ways are there to make a dipeptide?
2 - can make them from different combinations of the ends of the molecules
In the body, what is condensation polymerisation catalysed by?
enzymes
Describe the primary structure of a protein
sequence of amino acids
Describe the secondary structure of a protein
-primary structure of amino acids is held together in a particular shape by hydrogen bonds between amide hydrogen and carbonyl oxygen
-can be coiled into an alpha helix
-can be folded into a beta pleated sheet
Describe the tertiary structure of a protein
-overall 3D structure/shape of a protein
-extra bonds form between the peptide chain such as disulphide bridges and ionic bonds
What is a thiol functional group?
-SH
Two thiol groups make…
a disulphide (R-S-S-R’)
What role do disulphide bridges play in protein structures?
help to stabilise the tertiary structure
What may affect the formation of disulphide bridges/hydrogen bonds?
temperature and pH changes
How can mixtures of amino acids be separated?
thin layer chromatography
Describe briefly TLC?
-amino acids can be located on a chromatogram using developing agents like ninhydrin or UV light
-identified by Rf values
Write the two word equations that describe the condensation and breakdown of amino acids
amino acids —-> (cond. polym.) peptide (polyamide) + water
What are enzymes?
speed up chemical reactions in biological systems
Aside from breaking up a substrate, what else can enzymes do?
-join together two substrate molecules
-change the functional group of a substrate
What is the relationship between enzymes and optical enantiomers?
-enzymes active sites are stereospecific
-active sites only work on one enantiomer of a substrate
How do some drugs work?
they are inhibitors that block the active site of an enzyme and stop it from working
What is the challenge of finding drugs that will work with an enzyme?
-active site of an enzyme is very specific so is hard to find a drug that will fit snuggly in the active site
-more difficult if the molecule is chiral as only one enantiomer will fit into the stereospecific active site
What is an example of inhibitors used to treat high blood pressure?
ACE inhibitors - reduces the production of angiotensin so blood vessels enlarge and blood pressure is reduced
What other areas of medicine can inhibitors be used?
-antiviral
-anticancer
What does DNA stand for?
deoxyribonucleic acid
What does DNA contain?
all the genetic information of an organism
What is the monomer of DNA?
nucleotides
What is a nucleotide made up of?
-phosphate group
-pentose sugar
-base
Draw a phosphate ion
[drawing]
What is the pentose sugar in DNA?
2-deoxyribose
Name the four bases and their complementary base pairs
Adenine - Thymine
Guanine - Cytosine
When phosphate and sugar bond, what happens?
a water molecule is lost
How are mononucleotides joined together?
by covalent phosphodiester bonds between the phosphate group and pentose sugar
