Molecules of metabolism - Proteins and enzymes
February 2 and 4, 2004
Molecules
of metabolism - Proteins and enzymes
February 2 and 4, 2004
Readings: Starr, Ch 3, pps 42-45
Don't forget...Warm Up 3 is due Weds Feb
4 at 9:30 and Good For 3 at 11:30 Friday Feb
6!
It's Macromolecule #3: Proteins!
I. Proteins in everyday
life: 
General classes of proteins and their functions:
II. Proteins: the macromolecule and the monomer:
Proteins are about 50% of the dry weight of most cells, and are the most complex of the macromolecules we will talk about, because there are 20 different monomers or building blocks, called amino acids. The way these building blocks (amino acids) are put together gives each protein its own unique structure and function. Cells have thousands of different proteins, each with a specific function.
Even so, all proteins are polymers constructed from a set of 20 amino acid monomers linked end-to-end, up to thousands of amino acids long, each in a unique 3-D shape.
There
are 20 amino acid monomers: Each has the overall structure
shown at right.
1. A central Carbon (C)
2. An amino group (NH3)
3. A carboxyl, or acid, group (COO-)
4. A hydrogen (H), and
5. A variable region, the R group (side chain). There are 20 different R groups, whiich give the 20 different monomers their own special properties.
Click here to see models of all 20 amino acids!
Our bodies can make 11 of the ~20 amino acids
- the other 9 amino acids must be obtained from our diet.
You do not need to know the names of these amino acids!
III. Protein synthesis: an overview
To form
protein, individual amino acids are linked
together to form a peptide
bond. The protein chain grows one amino acid at a time, by linking one amino acid's amino group to the carboxyl
group of the next amino acid. by a
process called translation (more about this later in the
semester). A chain of amino acids is also known as a polypeptide.
Some proteins contain only one polypeptide chain while others, such as hemoglobin, contain several polypeptide chains all twisted together. The sequence of amino acids in each polypeptide or protein is unique to that protein, so each protein has its own, unique 3-D shape .[Image and quote]
How do cells know which proteins to make and which amino acids to link together? That is the function of DNA - our next macromolecule!
Two amino acid monomers....
...join together to make one polypeptide
IV. Protein structure - shape is everything!
1. There are four levels of protein structure - when a protein is synthesized from the instructions provided by DNA, it folds spontaneously into its shape reinforced by chemical bonds. If it doesn't form into the right shape, the protein often does not work! (Figure 3.17)
2. Diseases caused by proteins that do not form correctly: Changing just one amino acid - even if the protein is thousands of amino acids lond - can cause the protein to change shape and not work properly in cells.
Sickle cell disease - a 1-amino acid change causes the hemoglobin molecules in the red blood cell to deform, creating a 'sickled' shape that clogs in the blood vessels and organs of a person with SSD
Cystic fibrosis - loss of 1 amino acid causes a protein involved in salt transport to fail, causing sticky mucous to build up in the lungs and intestines of people with CF.
Muscular dystrophy - a loss of several amino acids in the muscle protein dystrophin causes improper muscle action.
Note: In these cases, the instructions are incorrect at the level of the gene (DNA), resulting in an incorrect protein. LOTS more on this later in the semester....
Objectives:
For Proteins, make sure you understand:
1. What the monomer is
2. What types of polymers result
3. What the functions of proteins are in cells.
4. The basic structure of an amino acid - 5 parts
5. What is the difference between essential and non-essential
amino acids?
You may want to make one big chart with room
for this information as well as for simple sketches.
See Table 3.1 = a nice summary table
