Lecture 19: How Genes Work

The two strands of DNA that for the double helix DNA molecule are ______ to each other.

Complimentary

What do complimentary DNA molecules do?

The complimentarity makes it possible for DNA to copy itself in preparation for cell division.

DNA replication is reliant on _____.

Base pairing:

1. DNA strands separate

2. New nucleotides pair w/ each template strand

3. Two identical DNA molecules are produced

• Three enzymes involved:

  • DNA helicase

  • DNA polymerase

  • DNA ligase

DNA and mRNA Proteins

DNA —> TAC, GGA, TCA, CCA, ACT

mRNA→ AUG, CCU, AGU, GGCU, UGA

Proteins: Methionine, Proline, Serine, Glycine, STOPS

Development of the Protein

1. DNA stays in the nucleus

• copied into mRNA

2. The cell needs to convert the RNA message into a protein

Proteins do the work

rRNA

Ribsomal RNA

Protein synthesis starts at the ______.

Codon

Where does Translation start and end?

Translation starts at the start codon (AUG) and ends when the ribosome reaches one of the STOP codons.

Ribosomes read mRNA one ___ at a time.

Codon

Protein is built one ____ ___ at a time.

amino acid

What are joined together to make a polypeptide?

Individual amino acids.

Translation occurs in ribosomes

tRNA delivers amino acids

• carries one amino acid

• anticodon matches the correct codon

• delivers the amino acid to the ribosome

Start of Translation

• The ribosome attaches to the mRNA

• The start codon (AUG) is recognized

• The first tRNA brings methionine (Met)

• Translation begins

Building a Protein

• tRNAs bring amino acids to the ribosome

• Codons are matched one at a time

• Amino acids are joined together

• The protein chain grows longer

End of Translation

A stop codon signals the end of translation.

• The completed protein is released

• The ribosome detaches from mRNA

mRNA

Carries the instructions

Ribosomes

Reads the message

tRNA

Delivers amino acids

Amino acids

Form the polypeptide

Gene Expression

Uses the information in a gene to make a protein

• Different cells express different genes

• Different genes produce different proteins

Stem Cells & Gene Expression

Stem cells contain the same DNA as other cells.

• Different genes are turned ON or OFF

• This process produces specialized cells

Gene expression can be ____ at several levels.

Regulated

How can cells turn genes ON or OFF?

• DNA accessibility

• Cells can control how much protein is produced