Molecular Genetics

Remember,

-DNA is a nucleic acid

-DNA is found in the nucleus

2 functions of DNA

To store and use info to direct cell activities

To copy itself exactly during cell division

Remember…

DNA is made up of monomers called nucleotides.

3 parts of a nucleotide in DNA

A phosphate group A 5-carbon sugar (deoxyribose) 4 different nitrogen bases

4 nitrogen bases

Adenine A Thymine T Cytosine C Guanine G

The base pairing rule

When nitrogen bases pair and form bonds, Adenine always pairs with Thymine and Cytosine always pairs with Guanine.

The structure of DNA

DNA is a double helix. Think of this as a twisted ladder.

This structure was discovered by James Watson and Francis Crick in 1953.

DNA is double stranded. The two strands are complimentary. When they unwind they serve as templates or guides for replication.

DNA replication

The enzyme DNA helicase “unzips” the 2 strands.

The now unpaired bases combine with free bases in the nucleus.

The enzyme DNA polymerase connects the nucleotides.

DNA is repaired by more than 20 “proof-reading” enzymes.

Practice DNA replication

T A G C A T G A T T A C C C G

A T C G T A C T A A T G G G C

Remember…

The sequence of nitrogen bases in DNA contains all the information that determines a cell’s structure and its function.

DNA…

…and the story of how to make a protein.

DNA vs RNA

5-carbon sugar is deoxyribose

DNA is a double stranded helix

4th nitrogen base is thymine

5-carbon sugar is ribose

RNA is a single strand

4th nitrogen base is uracil

Practice…

A U C G G A C U A G U A C G G U A C

U A G C C U G A U C A U G C C A U G

Three types of RNA

Messenger (mRNA)

Transfer (tRNA)

Ribosomal (rRNA)

Transcription

the process by which RNA is produced from DNA

this takes place in the nucleus

Practice…

DNA T A G C A T C T A G A G

A U C G U A G A U C U C

RNA

Translation

the process of assembling amino acids from information encoded in RNA

this takes place in the cytoplasm

Practice…

A U C G U A G A U C U C

Use the table in your textbook to translate the amino acid chain coded in this mRNA.

Protein Synthesis

the assembling of amino acids into a specific protein

occurs in the ribosomes

Vocab.

Codon-3 sequential bases in mRNA that “code” for a particular amino acid