Biology H-Mr.Willets Proteins/DNA
Proteins-
1) Proteins have many functions in organisms. There are structural proteins, enzymes, storage proteins, contractile proteins, transport porteins, signal proteins and defensive proteins. Each cell can make as many as 2000 different proteins. What an organism is like and how it functions depends on its cells making all the correct proteins.
2) Proteins are made by attaching amino acids together. A chain of amino acids is called a polypeptide. Polypeptides then join and twist into certain shapes to form the protein.
3) The primary structure of the protein is determined by the order of amino acids along the polypeptide chains. The secondary and tertiary structures of the protein are determined by how these chains join and twist.
4) There are about 20 different amino acids. Plants can make all of them. Animals must eat them. There are 10 amino acids you must have in your diet. These are called the essential amino acids. If you eat these, your cells can re-arrange them to make the other 10. Any protein that contains all 10 essential amino acids is called a high quality protein or a complete protein.
5) The complicated and important task of making sure the cell produces all of its proteins correctly is controlled by DNA. DNA is what chromatin is mostly made of. Chromatin strands are thin threads found in the nucleus of cells. These thicken during cell division and are called chromosomes.
DNA- Deoxyribonucleic Acid
1) Structure discovered in 1953- Watson, Crick, Wilkins
2) DNA is a macro-molecule made of several different smaller molecules joined in a specific pattern.
These molecules are: Deoxyribose sugar, phosphate, and 4 nitrogen bases: adenine, guanine, cytosine and thymine. Adenine and guanine are double ringed molecules called purines. Cytosine and thymine are single ringed molecules called pyrimidines. (see other side)
These molecules are put together in groups called nucleotides- a nucleotide consists of a sugar molecule, a phosphate and one of the 4 nitrogen bases.
Nucleotides then join to form DNA . The DNA molecule is in the shape of a twisted ladder. This shape is like a spiral staircase and is called a double helix. The sides of the "ladder" are alternating molecules of sugar and phosphate. The rungs of the ladder are pairs of nitrogen bases. (see other side)
The pairs of nitrogen bases that can join are either: guanine with cytosine or adenine with thymine. These bases pair up this way because of the size of the molecules and the places that they can join (see other side) In other words, the members of a base pair are complementary to each other
3) DNA can make exact copies of itself. This process is called replication. Without replication, reproduction could not occur.
4) DNA replicates making only one error per billion nucleotides. Special enzymes correct these errors and repair any damage done to the DNA by normal wear and tear. There is a theory that aging is a result of the DNA wearing out and not being repaired.
5) DNA molecules have thousands of nucleotides. The order of these along the molecule is different for each piece of DNA. This order of nucleotides has the chemical information about making proteins. It is called the genetic code.
DNA Structure-
Look at the structure of deoxyribose sugar shown below. What is the formula for this sugar?_______________
What is odd about this formula? ___________________________How does this explain the name of the sugar?_______________________________________________________________________________
What do you think the formula for "ribose sugar" is? ________________
The structural formulas for the 4 nitrogen bases are shown below. In what way would the rungs of the"DNA ladder" be messed up if adenine and guanine paired up and thymine and cytosine paired up? (hint-size)__________________________________________________________________________
The dotted lines between bases represent "hydrogen bonds". These are weak connections between molecules. Notice that there is a hydrogen atom involved in each case. Also notice that the hydrogen atom involved is attached to a nitrogen atom and lines up opposite a nitrogen or an oxygen on the other molecule.
Fold the paper in such a way as to line up the adenine and the cytosine. Would they be able to form hydrogen bonds? _______ Although you cannot fold the paper to see it, thymine and guanine would have the same problem.
What are the two reasons why the rungs in the ladder have to be A-T and G-C and no other possibilities?
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The diagrams below show a small section of DNA using different shapes to represent the various parts. One diagram shows the ladder "untwisted". The other shows the double helix structure. In the untwisted model, it is clear that the phosphates stick out from the sides of the ladder. Both show that the base pairs are attached to the sugar molecules on the ladder's sides.
