Download 13.3 RNA and Gene Expression

13.3 RNA and Gene Expression
Mrs. Stipanovich
How do genes (DNA) code for
proteins?



DNA contains the instructions or
code for the production of proteins
in the cell.
This is known as gene expression.
Proteins determine the structure
and function of organisms (traits).
How do genes (DNA) code for proteins?

Two processes:




Transcription: DNA ----- RNA
Translation: RNA ------ Protein
Proteins are made on the ribosomes
that are located in the cytoplasm of
the cell. DNA in the nucleus and is
too large to leave the nucleus and
travel to the cytoplasm.
How can the genetic code get to the
ribosomes?
RNA- Ribonucleic Acid

Similar to DNA with three
differences:
1. Made up of one strand
2. Contains the base Uracil (U)
instead of Thymine.
3. Contains the sugar ribose instead
of deoxyribose.
Three Types of RNA
1.
2.
3.
Messenger (mRNA) – carries copies of
the instructions for making proteins
from the DNA (in the nucleus) to the
ribosomes in the cytoplasm of the
cell.
Ribosomal (rRNA) – helps to
assemble amino acids to make
proteins on the ribosomes.
Transfer (tRNA) – transfers specific
amino acids to the ribosome for
assembly into proteins
Transcription: Reading the gene

Transcription is the copying
(transcribing) of a certain gene
on DNA onto RNA.
Steps of Transcription
1.
2.
3.
The DNA strand has a code for
“start,” the RNA Polymerase is
triggered to start reading the code
at this spot.
RNA Polymerase unzips the DNA to
make a copy of one section of it.
The RNA nucleotides line up to
make a copy of the DNA.
Transcription
RNA
Codons





Every word in DNA “language” is a
three letter word known as a codon.
Each codon is code for a certain
amino acid.
When several amino acids are put
together you get a protein.
There are twenty different amino
acids that make up all proteins.
Proteins control your traits.
Translation: RNA to Proteins

Translation is essentially decoding
the codons to know which amino
acids the cell should make.
Steps of Translation
1.
mRNA attaches to a ribosome
Steps of Translation
2. Each mRNA codon moves along the
ribosome and the tRNA anticodon
brings the correct amino acid to
the ribosome.
Steps of Translation
3. Peptide bonds form between the
amino acids and the tRNA molecule
is released.
Steps of Translation
4. The process continues until a stop
codon is reached. There are 3 stop
codons: UAA, UAG, UGA
Now you try!




Use your codon wheel to translate
the following codons into amino
acids.
AUG
UGU
GGG