Gene regulation

How does DNA make different cells?

• All cells have a full set of DNA

• Not all the DNA is expressed in each one

• Promoters and repressors allow only certain genes to be expressed (make protein)

Nerve, cardiac, muscle, white blood cells

The gene that breaks down lactose is repressed

How it works• When lactose is added, it binds to the

repressor protein.

Activation

When lactose binds to the repressor, it movesaway, allowing the protein to be made

Left side: why do you think this process is called a “positive” feedback loop?

Eukaryotic Gene Regulation• Many eukaryotic genes have a sequence

called the TATA box that helps to position

RNA polymerase.

Direction of transcription

Differentiation• From a fertilized egg to an

adult, cells grow and divide.

• They also differentiate into many different types of cells

• Hox genes control that differentiation

• They are inherited from the genes of our common ancestors

Gene mutation

• Point mutation: the subtraction, addition or substitution of a single nucleotide

• Changing a nucleotide will change the codon– Can change the amino acid

• Subtraction and addition can cause a “Frame shift” making all amino acids downstream change – This can completely change a protein – Most mutations are harmful

Left side: why don’t all mutations causes changes to the amino acids?

Not all mutations are equal

• If you put a hox gene for “eye” from a fruit fly into a mouse embryo, it will develop into an mouse eye.

• If you move a hox gene for an eye from the head to the back of a fruit fly embryo the eye will develop on the back

• Small genetic changes can make large changes to an organism.

Summaryreview

1. What do hox genes do?

2. What are repressors and promoters?

3. What causes a frame shift?