Lecture #12—Evidence from Biochemistry

In the last 150+ years the field of biochemistry developed and has given us great insight as to how evolution has occurred. We now understand how genes actually control the cell and give us the traits we see.

Mendel’s factors are now called genes and they control the cell. Genes are made of the chemical DNA (deoxynucleic acid). The DNA sends chemical instructions as the chemical RNA (ribonucleic acid) to ribosomes to make particular proteins. So a gene is a sequence of nucleotide bases that code for a polypeptide. These polypeptides (proteins) function in 2 ways: they are part of cell structures such as cell membranes and they are enzymes. The latter control which chemical reactions go on in the cell.

You need to know the structure of DNA and how it differs from RNA

You need to know how DNA makes copies of itself which prior to each time the cell divides. So it is an essential step occurring before mitosis and meiosis.

The order of the 3 nucleotides in an RNA codon determines which one of the ~20 amino acids will be inserted into a protein at a particular place. So to insert the amino acid alanine, the order of the nucleotides must be Guanine, Cytosine and then any other of the nucleotides (uracil, cytosine, adenine, or guanine = GCU or GCC or GCA or GCG). See below. Learn how to read the table.

By analyzing the sequence of amino acids in given proteins we can measure how closely related two organisms are. Even better, by measuring the sequence in sections of DNA or RNA we can determine their family relationships more directly.

Terms/Concepts to Define

Gene

Base units of DNA and RNA

DNA triplet

RNA codon

Transcription

Translation

mRNA

tRNA

Ribosome

Can you answer these questions?

1)What is the chemical nature of DNA

2)What is the chemical structure of RNA

3)How does DNA control chemical reactions in a cell?

4)Describe how DNA makes copies of itself just before cell division.

6. What DNA triplets will code for the above RNA codons?

7. Describe the Central Dogma of Molecular Biology.