1. Proteins

2. Multipurpose molecules
Proteins:
Multipurpose molecules

3. Proteins Examples muscle skin, hair, fingernails, claws pepsin insulin
collagen, keratin
pepsin
digestive enzyme in stomach
insulin
hormone that controls blood sugar levels
pepsin
collagen (skin)

4. Proteins Function: many, many functions hormones movement
signals from one body system to another
insulin
movement
muscle
immune system
protect against germs
enzymes
help chemical reactions

5. Amino acids H O | H || —C— C—OH —N— R Structure central carbon
amino group
carboxyl group (acid)
R group (side chain)
variable group
different for each amino acid
confers unique chemical properties to each amino acid
like 20 different letters of an alphabet
can make many words (proteins)
—N— H R
Oh, I get it!
amino = NH2
acid = COOH

6. Proteins —N— H | —C— C—OH || O Building block = amino acids –
20 different amino acids
There’s 20 of us…
like 20 different letters in an alphabet! Can make lots of different words
—N— H |
—C—
C—OH || O
variable group

7. Effect of different R groups: Nonpolar amino acids
nonpolar & hydrophobic
Why are these nonpolar & hydrophobic?

8. Effect of different R groups: Polar amino acids
polar or charged & hydrophilic
Why are these polar & hydrophillic?

9. Sulfur containing amino acids
Form disulfide bridges
covalent cross links betweens sulfhydryls
stabilizes 3-D structure
H-S – S-H
You wondered why perms smell like rotten eggs?

10. Amino Acids Essential Amino acids
Amino acids that the body cannot synthesize from simpler compounds; they must be obtained from the diet

11. —N— H | —C— R C—OH || O —N— H | —C— R C—OH || O
Amino acid chains
Proteins
amino acids chained into a polymer
—N— H |
—C— R
C—OH || O
—N— H |
—C— R
C—OH || O

12. —N— H | —C— R C—OH || O —N— H | —C— R C—OH || O
Amino acid chains
Proteins
amino acids chained into a polymer
—N— H |
—C— R
C—OH || O
—N— H |
—C— R
C—OH || O
Carboxyl
group
Amino
group

13. —N— H | —C— R C— || O —N— H | —C— R C—OH || O OH H
Amino acid chains
Proteins
amino acids chained into a polymer
—N— H |
—C— R C— || O
—N— H |
—C— R
C—OH || O OH H

14. —N— H | —C— R C— || O —N— H | —C— R C—OH || O H2O
Amino acid chains
Proteins
amino acids chained into a polymer
—N— H |
—C— R C— || O
—N— H |
—C— R
C—OH || O
Peptide bond- The amide linkage that holds amino acids together in polypeptides
H2O

15. Amino acid chains Proteins Each amino acid is different
amino acids chained into a polymer
Each amino acid is different
some “like” water & dissolve in it
some “fear” water & separate from it

16. Amino acid chains Amino terminus Carboxyl terminus
The free amino group at one end of the polypeptide
Carboxyl terminus
The free carboxyl group at one end of a polypeptide

17. Water-fearing amino acids
Hydrophobic
“water fearing” amino acids
try to get away from water in cell
the protein folds

18. Water-loving amino acids
Hydrophillic
“water loving” amino acids
try to stay in water in cell
the protein folds

19. For proteins: SHAPE matters!
Proteins fold & twist into 3-D shape
that’s what happens in the cell!
Different shapes = different jobs
growth hormone
hemoglobin
pepsin
collagen

20. It’s SHAPE that matters!
Proteins do their jobs, because of their shape (conformation)
Unfolding a protein destroys its shape
wrong shape = can’t do its job
unfolding proteins = “denature”
temperature
pH (acidity)
unfolded “denatured”
In Biology,
it’s not the size,
it’s the SHAPE that matters!
folded

21. Protein Folding Shape comes from how the protein folds
There are 4 levels of folding in proteins

22. Primary (1°) structure Order of amino acids in chain
amino acid sequence determined by gene (DNA)
slight change in amino acid sequence can affect protein’s structure & its function
even just one amino acid change can make all the difference!
Sickle cell anemia: 1 DNA letter changes 1 amino acid = serious disease
Hemoglobin mutation: bends red blood cells out of shape & they clog your veins.
lysozyme: enzyme in tears & mucus that kills bacteria

23. Secondary (2°) structure
“Local folding”
folding along short sections of polypeptide
interactions between adjacent amino acids
H bonds
weak bonds between R groups
forms sections of 3-D structure
-helix
-pleated sheet
It’s a helix or B sheet within a single region. Can have both in one protein but a specific region is one or another
Coiled (α-helix)
Hair - Can stretch, perms change the protein structure
Hydrogen bonds
Between chains and parts of chains
Disulfide bonds
Occur between chains
β-sheet
Eg. Silk
Doesn’t stretch
Hydrogen bonds between side chains

24. Secondary (2°) structure

25. Tertiary (3°) structure
“Whole molecule folding”
interactions between distant amino acids
hydrophobic interactions
cytoplasm is water-based
nonpolar amino acids cluster away from water
H bonds & ionic bonds
disulfide bridges
covalent bonds between sulfurs in sulfhydryls (S–H)
anchors 3-D shape
How the whole thing holds together
Tertiary Structure
Globular shape (only helices)
enzymes
Each protein folds in a specific way
Folding of the secondary structure
Bonding between R groups (side chains)
Hydrophobic interactions
Nonpolar side chains, away from water
Hydrogen bonds between side groups
Ionic bonds between +ve and –ve charged R groups (weak)
Disulfide Bridges
Strong covalent bonds
Between aa with sulfyhdryl groups on their side chains
Between cysteine bonds

26. Quaternary (4°) structure
More than one polypeptide chain bonded together
only then does polypeptide become functional protein
hydrophobic interactions
Protein structure video
Structure equals function wonderfully illustrated by proteins
Collagen is just like rope -- enables your skin to be strong and flexible.
hemoglobin
collagen = skin & tendons

27. Protein structure (review)
R groups
hydrophobic interactions
disulfide bridges
(H & ionic bonds) 3°
multiple polypeptides
hydrophobic interactions 1°
sequence determines structure and…
structure determines function.
Change the sequence & that changes the structure which changes the function.
amino acid sequence
peptide bonds 4° 2°
determined by DNA
R groups
H bonds