1. Biochemistry Macromolecules, Proteins, Amino Acids4

2. Amino Acids https://www.youtube.com/watch?v=G9BkFqVkQ-g 7 minutes4

3. Introduction to Biochemistry
Most biologically important macromolecules are:
1) proteins
2) polysaccharides (carbohydrates)
3) nucleic acids
4) Oils and fats
All are polymers made via Condensation reactions and destroyed by Hydrolysis.

4. Amino Acid Properties are soluble in water
They can act as either an acid or a base because they are Zwitterions (Zwi = 2 in German) have a positive &
a negative charge
Thus they are ionic and so:
1) Have high melting temperatures
2) Are solids (and colourless)
3) As they are ionic and charged they
are soluble in water
4) Chemically they can behave as
buffers
5) They are ALL chiral (except
Glycine) therefore they are
enantiomers

5. The asymmetry of their mirror images
Amino Acids are optically active molecules or they have chiral carbons (4 DIFFERENT groups attached). One exception is the achiral glycine where the R-group is hydrogen).
The asymmetry of their mirror images
makes them non-superimposable. They
are called enantiomers (anti - opposite)

6. Polypeptides and Proteins
Proteins are polyamides made from 20 amino acids make proteins in humans. There are actually more than 700 amino acids counted so far.
When formed by amino acids, each amide group is called a peptide bond (amide bond).
Peptides are formed
by condensation of the
-COOH with the NH2
group of another
amino acid. .

7. Acid-Base Behavior of Amino Acids4

8. Amino Acids
While their name implies that amino acids are compounds that contain an —NH2 group and a —CO2H group, these groups are actually present as —NH3+ and —CO2– respectively.
How do we know this?

9. high melting point (when heated to 233°C )
Properties of aa’s
Ex: glycine
high melting point (when heated to 233°C )
soluble in water; not soluble in nonpolar solvent
consistent with ions like this
Not molecules like this –
• • O
H3NCH2C •• + O OH
H2NCH2C ••
• •
Thus we know it is a zwitterion or dipolar ion

10. Acid-Base Properties of Glycine
The zwitterionic structure of glycine also follows from considering its acid-base properties.
Start with the structure of glycine in strongly acidic solution, say pH = 1, then ask the question, what would glycine look like?
At pH = 1, glycine exists in its protonated form O OH
H3NCH2C + ••
• •

11. Acid-Base Properties of Glycine
Now ask yourself "As base is added and the pH is raised, which is the first proton to be removed?
typical carboxylic acid: pKa ~5
typical ammonium ion: pKa ~9
OOH
H3NCH2C +
The more acidic proton belongs to the COOH group.
In fact, glycine is stronger than a typical carboxylic acid because the positively charged N acts as an electron-withdrawing group, making the H more likely to leave.

12. Acid-Base Properties of Glycine
Now continue to raise the pH, and eventually the H+ attached to N can be removed.
The pKa for removal of this proton is This value is about the same as that for NH4+

13. The pKa of glycine is approx 6.0.
Zwitterionic structure is neutral the pH is called isoelectric point.
H+ gone in base
H+ attaches in Acid
The pKa of glycine is approx 6.0.

14. Protein Structure
All 4 structures 2 minutes
Primary structure is the amino acid sequence. Ex: aa-aa-aa-aa-aa
Secondary structure is how the amino acids in sequence fold up.
Ex:a-helixes & b-sheets
via H-Bonds.
Tertiary the 3-D folding of
the secondary
structure.
Also, disulfide bonds from
cysteine form here
Quaternary Final product, final structure, when all the subunits or polypeptides are brought together to make the whole thing.

15. 1O Structure Consider a peptide with two amino acids
AA1
AA2
x = different molecules
AA1
AA2
AA3
20 x x 20 (or 203 ) = different molecules
For 100 amino acid protein the # of possibilities are:
The total number of atoms in the universe is

16. 2o structure: b-strands
Inter-chain
H-bonds

17. 2o structure: a-helixes
Intra-chain
H-bonds
Alpha Structure 3 minutes

18. 2o structure: a-helixes

19. 3o 4o Structures 3o 4o HbA 22 tetramer Hb monomer (or myoglobin)
(multimeric)
Hb monomer (or myoglobin)

20. Enzymes Active (catalytic) site is a crevice which binds a substrate.
1500 enzymes have been found.
Enzymes are proteins which act
as catalysts(there may be
30,000 enzymes in a human.
Active (catalytic) site is a
crevice which binds a
substrate.
Lock & key metaphore.

21. Enzyme Inhibition

22. The Structure of DNA
All life on earth uses a chemical called DNA to carry its genetic code or blueprint. In this lesson we be examining the structure of this unique molecule.
{Point out the alligator’s eyes in the first picture.} By the way, can you make out what this is?
***************************************************************
[The goal of this presentation is to introduce high school biology students to the chemical structure of DNA. It is meant to be presented in the classroom while accompanying the teacher’s lecture, under the control of the teacher.]

23. The Shape of the Molecule
DNA is a very long polymer.
The basic shape is like a twisted ladder or zipper.
This is called a double helix.
{Show students a model of the double helix. Explain what a spiral is and a helix is.}

24. The Double Helix Molecule
The DNA double helix has two strands twisted together.
We will take apart the DNA molecule to see how it is put together.
First, we will look at one strand.

25. The teeth are nitrogenous 4 nitrogen bases.
One Strand of DNA
The backbone of the molecule is alternating phosphates and deoxyribose sugar
The teeth are nitrogenous 4 nitrogen bases.
Cytosine C Thymine T Adenine A Guanine G
nucleotide
deoxyribose
{Point to the 3-D mode, if you have one, to show the parts as you discuss them.}
phosphate
bases

26. The teeth are the nitrogenous bases but why do they stick together?
Two Stranded DNA
Remember, DNA has two strands that fit together something like a zipper.
The teeth are the nitrogenous bases but why do they stick together?
{Point to the 3-D model to show the parts as you discuss them.}

27. Hydrogen Bonds
The bases attract each other because of hydrogen bonds.
Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA.
The bonds between cytosine and guanine are shown here with dotted lines C N O

28. Cis-Plantin
2 minutes