Lecture Notes-12 Biology 1004

North Arkansas College

Topic: Macromolecules

1. Composed of a purine/pyrimidine base, a five-carbon sugar (pentose) and a phosphate.
2. Purines are double ring nitrogen and carbon. There are two types of purines: adenine (A) and guanine (G). They differ in chemical groups substituted onto the purine ring. Pyrimidines are single-ring compounds of carbon and nitrogen. These are cytosine (C) and thymine (T).
3. We find nucleotide in DNA (A,G,C,T), RNA (A,G,C,U), ATP (energy carrier molecules) and coenzymes (NAD, NADP+ necessary for enzyme activity). Each ATP molecule contains between 6,000-12,000 calories of energy. We do not store ATP, but we use 100 lbs. per day. ATP (adenosine triphosphate) - ~P is a high-energy bond.

A complete molecule of DNA contains information equivalent to 8,000 bibles. This information fits into every cell, however, only a portion is expressed.

1. DNA is made up of:

1. Two purines and two pyrimidines:
2. adenine & thymine (purines)
3. guanine & cytosine (pyrimidines)
4. Five carbon sugar (deoxyribose)
5. Phosphate (PO₄)

2. How are the nucleotide put together to make up a single strand of DNA?

1. There are no links directly between purines and pyrimidines.
2. Links are through phosphate bonds between the sugars. The PO₄ links #3C of 1 nucleotide to the #5C of the next sugar. This dictates the orientation of the 2 stands of DNA.
3. Phosphate bonds hold the individual stands of nucleotides together. They are very strong bonds.

1. In most organisms, DNA occurs as 2 strands (2X).
2. These two strands are exactly complimentary to each other and A always pairs with T (A-T), and G always pairs with C (G-C).
3. The 2 strands are held together by weak hydrogen bonds.
4. The 2 strands have opposite orientation, or they are antiparallel to each other. The 5’ - 3’ and the 3’ - 5’. The 5’ à 3’ is sense.
5. A molecule of DNA is approximately 2.5 meters long. Most bacteria average 0.2 m m to 2 m m in length; 10 m m to 100 m m for eucaryotes.
6. The DNA molecule must be tightly coiled to fit into the cell. This occurs by:

1. Forming a double helix in which the 2 strands twist around each other.
2. Higher organisms (eucaryotes) contain protein linkers within the DNA called histones. The DNA can wrap around the histones to occupy less space in the cell.
3. The double helix can fold on itself several different times to form a super helix.

RNA is similar to DNA, but with several exceptions:

1. The 5C sugar ribose replaces deoxyribose.
2. The pyrimidine base uracil replaces thymine.
3. RNA is usually just 1 strand.

There are Three Types of RNA

1. Messenger RNA (mRNA) carries a copy of DNA and is responsible for the type of protein that’s made.
2. Ribosomal RNA (rRNA) makes up part of the structure of ribosomes (60% RNA).
3. Transfer RNA (tRNA) transfers the amino acids from a "pool" into the cytoplasm, and then places it into the polypeptide being formed onto the mRNA template. The mRNA template dictates the sequence of amino acids into new proteins.

The major process in living organisms revolves around the conversion of stored information into DNA into usable products as proteins. Protein is the primary product produced because:

1. Proteins are the major structural component of the cell.
2. Those components that are not protein are produced by enzyme reactions, which are usually protein. This process is DNA (stored information) - protein. This process takes place in 2 key steps.

A copy of the DNA is made in the form of mRNA.

The ribosomes read the mRNA and translate it into useable protein. DNA - mRNA - useable protein. In this process we go from the 4-letter language of DNA (A, G, C, T) to a protein language (20 letters in form of naturally occurring amino acids). How does this occur?

The information is stored in DNA in coded form. Three bases in sequences (A AA, A AC) specify each amino acid. This is known as the triplet code, and each triplet is called a codon. The codon is equal to a triplet of 3 bases that specify 1 amino acid.

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