Honors BiologyGENE EXPRESSION

Construct and revise an explanation based on evidence for how carbon, hydrogen, and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon-based molecules.

Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells.

OBJECTIVES

What is gene expression?The process of using DNA

code to make protein

GENE EXPRESSION: WHAT

When does gene expression occur?All the time!Example: during development (Hox genes and body

plan)Example: in your cells NOW (such as hormones )

GENE EXPRESSION: WHEN

Who goes through gene expression?

All cellsAble to turn on/turn off

Cell type dependent Muscle cells turn on the genes for

what they need (like making actin), turn off the genes for what they don’t (like making lactase)

Cellular need dependent Turn genes on/off depending on

cell’s needs at the time (such as food molecules present needing digestion)

Environmental conditions Soil pH and hydrangeas (the more

acidic the pH, the bluer the flower)

GENE EXPRESSION: WHO

Human genes cannot all be active at the same time If they were, all the cells in our bodies would look the

same and have the same function(s)For specialization to occur, some genes or gene

products must be active while others are turned off or inactive

GENE ACTIVATION

Where in the cell does gene expression occur?

Cell structures and their function: Nucleus

Store DNA Ribosome

Make protein Rough endoplasmic

reticulum Ribosomes attach

Vesicles Transport proteins around

cell Golgi body

Modify/complete protein Cell membrane

Control entry/exit of materials

Vacuoles Store materials

GENE EXPRESSION: WHERE

Why do organisms express genes?Proteins carry out the essential functions of life

through systems of specialized cells

GENE EXPRESSION: WHY

How are genes expressed?2 steps:1. Transcription

In nucleus mRNA is made from DNA

2. Translation In cytoplasm Protein is made from mRNA

GENE EXPRESSION: HOW

1. DNA section with desired gene is unzipped by RNA polymerase

2. RNA polymerase adds complementary nucleotides, mRNA strand is made

3. When a stop sequence is reached, mRNA separates from DNA and DNA is re-zipped

4. mRNA leaves the nucleus

TRANSCRIPTION

1. mRNA finds a ribosome2. Ribosome scans mRNA

for the start codon (AUG)3. tRNA with the

corresponding anti-codon carries in amino acid

4. Ribosome shifts down, reads the next codon

5. Next tRNA moves into place

6. Amino acids bond together

7. Repeats until a stop codon is reached and protein is released

TRANSLATION

How does the cell determine what amino acid goes with the mRNA’s codon?

CODON = AUG

Start in the center and work your way out

A

U

G

Amino acid is methionine

Try finding the amino acid for the codon ‘CUA’

LEUCINE

Codon Table