Transcript 2_Proteins - Northwest ISD Moodle

Discuss the following with your
group and be prepared to discuss
with the class
1. Why is the shape of a molecule important?
2. How is a covalent bond different from ionic?
3. How are hydrogen bonds different from covalent?
We are beginning our first Unit today: Bio-Molecules
Right now, the test is set for Tuesday, Sept 17th
AP Biology
Functional groups
-parts of organic molecules that are
involved in chemical reactions
They give organic molecules distinctive
properties
hydroxyl
amino
carbonyl (ketones and aldehydes)
sulfhydryl
carboxyl
phosphate
Polymers
- long molecules built by linking repeating
building blocks in a chain

monomers
 building blocks
 repeated small units

covalent bonds
H 2O
HO
H
HO
HO
H
H
How to build a larger Bio-molecule
 Dehydration Synthesis (also called Condensation Reaction)

joins monomers by “taking” H2O out
 one monomer donates OH–
 other monomer donates H+
 together these form H2O

requires energy & enzymes
HO
H 2O
H
HO
H
enzyme
This is an example of
an Anabolic,
endergonic reaction.
HO
H
How to break down a larger molecule
 Hydrolysis (also called Digestion)

use H2O to breakdown polymers
 reverse of dehydration synthesis
 takes off one monomer at a time
 H2O is split into H+ and OH–
 H+ & OH– attach to ends
requires enzymes
 releases energy
H2O

This is an example of
an Catabolic,
exergonic reaction.
HO
HO
enzyme
H
HO
H
H
Bio-Molecules
 Large organic molecules formed by
smaller molecules bonding together

macromolecules
 4 major classes of
macromolecules:
carbohydrates
 lipids
 proteins
 nucleic acids

Proteins
Multipurpose
molecules
AP Biology
2008-2009
Proteins
- Most structurally & functionally diverse group
 Various functions:






enzymes (speed up metabolism)
structure physical stability and movement
(keratin-hair/nails/skin, collagenbones/cartilage/tendons, myosin-muscles)
transport (hemoglobin- in red blood cells,
proteins in cell membranes)
cell communication/regulatory
 signals (insulin & other hormones)
 receptors
defense (antibodies/recognize foreign
invaders)
storage (hold amino acids for later use)
Amino acids
Protein monomer (building block)
 central carbon
 Two functional groups:
carboxyl group (acid)
 amino group

H O
H
| ||
—C— C—OH
—N—
|
H
R
 R group (side chain)
 variable group that is
different for each amino acid
 gives unique chemical
properties to each amino acid
 like 20 different letters of an
alphabet
 can make many words (proteins)
Peptide Bonds – Linking of Amino Acids
Effect of different R groups:
Nonpolar amino acids
 nonpolar & hydrophobic
Effect of different R groups:
Polar amino acids
 polar or charged & hydrophilic
Building proteins
 Peptide bonds
covalent bond between NH2 (amino) of
one amino acid & COOH (carboxyl) of
another
 C–N bond

H2O
dehydration synthesis
peptide
bond
Building proteins
 Polypeptide chains have direction
N-terminus = NH2 end
 C-terminus = COOH end
 repeated sequence (N-C-C) is the
polypeptide backbone

Protein structure & function
 Function depends on structure

3-D structure
 twisted, folded, coiled into unique shape
pepsin
hemoglobin
collagen
Primary (1°) structure
 Order of amino acids in chain
amino acid sequence
determined by genes (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!
(Example of structure determining function)
Sickle Cell Anemia
What type of mutation is
this?
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
Tertiary (3°) structure
 “Whole molecule folding”

interactions between distant amino acids
and R groups
Quaternary (4°) structure
 More than one polypeptide chain bonded
together
collagen = skin & tendons
hemoglobin
Protein denaturation
 Unfolding a protein

conditions that disrupt H bonds and
ionic bonds
 temperature
 pH
 salinity

alter 2° & 3° structure
 alter 3-D shape

destroys functionality
 some proteins can return to their functional shape
after being denatured, many cannot
 Enzymes
a type of protein that acts as a catalyst, speeding
up chemical reactions
Substrate
(sucrose)
Glucose
H 2O
Fructose
Some enzymes require other atoms or molecules in order to
function:
-Cofactors: inorganic ions, such as iron, copper, or zinc that
bind to enzymes in order to help break down specific
substances.
-Coenzymes: organic molecules that are required by certain
enzymes to carry out catabolic reactions.