Nucleic Acids And Protein Synthesis

I. What are Nucleic Acids?

A. Nucleic acids are organic compounds that control all the activities of a cell.

B. The cells of all organisms, except viruses, contain both types of nucleic acids.

C. 2 types of nucleic acids

DNA (Deoxyribonucleic Acid) known as the code of life

a. The structure of DNA was discovered by James Watson and Francis Crick in 1953.

b. The structure of DNA is a double helix (looks like a spiral staircase). If uncoiled DNA would look like a ladder.

c. Each side of the DNA ladder made of alternating phosphate groups and sugar molecules. Each rung of the DNA ladder is made of 2 nitrogen bases held together by hydrogen bonds.

1. Each sugar, phosphate and base make up a nucleotide.

d. DNA is made of 4 bases:

Adenine 2. Guanine (both called purines and made of a double ring carbon and nitrogen atoms)

3. Thymine 4. Cytosine (both called pyrimidines and made up of single ring carbon and nitrogen atoms)

e. Each rung of the DNA ladder is made up of one purine and one pyrimidine.

Adenine bonds only with thymine. 2. Guanine bonds only with cytosine.

f. DNA has the ability to build an exact copy of itself.

1. A complete copy of DNA must be made before a cell can divide.

2. During replication the ladder splits down the middle (unzips) and a matching nucleotide joins on each nucleotide of the original.

2. RNA (Ribonucleic Acid)

a. There are 3 major structural differences between DNA and RNA:

1. RNA is a single strand: It does not bond to a complimentary strand like DNA (It makes ½ a ladder).

2. RNA has a 5 carbon ribose sugar (it has one more oxygen molecule than a deoxyribose sugar).

3. RNA uses the base uracil instead of the base thymine 3. RNA uses the base uracil instead of the base thymine. The bonding rule stays the same with this exception) (AU GC)

b. 3 different types of RNA.

1. Messenger RNA (mRNA) carries the information(or message) from the nucleus to the ribosome.

The message is the instruction as to how amino acids are put together to build specific protein. It serves as a template for amino acid assembly.

2. Transfer RNA (tRNA) picks up and carries amino acids to the ribosomal RNA at the ribosome.

Made in 20 or more varieties that bond to only one type of amino acid.

3. Ribosomal RNA (rRNA) makes up part of the ribosome.

II. Protein Synthesis (The making of proteins from amino acids)

A. Important process because without proteins there would be no life.

B. Steps of protein synthesis:

1. Transcription (making RNA from DNA)

a. DNA unzips just like in replication except this time the nucleotides that pair up have a ribose sugar and thymine is replaced by uracil.

1. This strand now unzips, leaves the nucleus and attaches to a ribosome: the original DNA will bond back together.

b. On the mRNA each combination of 3 bases is called a codon (a 3 letter code word for a specific amino acid: (ex. AGC, GUC)

1. There are 64 possible codons 1. There are 64 possible codons. Most code for amino acids, but a few are start and stop signals.

2. Translation – assembling amino acids to make protein.

a. Each combination of 3 bases on transfer RNA is called an anticodon (bases that pair up with a codon on the mRNA)

b. Transfer RNA pairs up with the mRNA bringing an amino acid with it b. Transfer RNA pairs up with the mRNA bringing an amino acid with it. These amino acids bond together to form a protein.

c. Proteins can be several amino acids long or just a few.