12-3 R

NA AND P

ROTEIN

SYNTH

ESIS

1. TH

E STR

UCTURE O

F

RNA

• RNA is made of:• long chains of nucleotides• Ribose• Single-stranded• Has Uracil instead of thymine

• An RNA molecule is a working copy of a single gene

• Genes- coded DNA instructions that control the making of proteins w/i the cell

DISCUSS:

• What is a protein?• List the protein you ate

today and/or yesterday• What role do proteins

play in your body functions?

2. TYP

ES OF

RNA

• There are 3 main types of RNA:• Messenger RNA (mRNA)– carry

copies instructions from genes for putting together amino acids into proteins. Carry “messages” from DNA to the rest of the cell.

• Ribosomal RNA (rRNA)- makes up a major part of the ribosome (proteins are put together here)

• Transfer RNA (tRNA)- transfers each amino acid to the ribosome as it is specified by coded messages in mRNA.

3. TRANSCRIP

TION

• Transcription happens when: RNA polymerase connects to DNA &

separates the DNA strands. RNA polymerase (an enzyme) then uses

one strand of DNA as a template (model) to put together nucleotides into a strand of RNA.

Transcription- RNA molecules are made by copying a part of the nucleotides from a DNA sequence

• RNA Polymerase- an enzyme that binds to DNA & separates the DNA strands during transcription

• Promoters- An area of DNA nucleotide sequences where RNA begins transcription

TRANSCRIPTION

RESULTS OF TRANSCRIPTION:

DNA strand: AATGCTGCGGATC

mRNA strand: UUACGACGCCUAG

2. RNA E

DITIN

G

• Introns- DNA sequences of nucleotides that do not code for a protein

• Exons- sequences that does code for a protein

• The introns are cut out of RNA molecules.

• The exons are then spliced together to form mRNA.

3. THE G

ENETIC C

ODE

• Is universal in all organisms• Proteins are made by putting together a lot of

polypeptides.• Polypeptides are a combination of any or all

20 different amino acids. The order of the amino acid determines the property of the protein

• mRNA’s language is called the genetic code which is 3 “letters” transcribed from DNA.

• The code is written using four “letters” (the bases: A, U, C, and G

• Codon -three nucleotides that are next to each other on mRNA that specify a particular amino acid

THE GENETIC CODE

3. TRANSLA

TION

• Takes place on the ribosomes• Translation- the decoding of an mRNA

message into a polypeptide chain (protein)

1. Translation begins when an mRNA molecule attaches to a ribosome.

2. As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought into the ribosome by tRNA.

3. In the ribosome, the amino acid is transferred to the growing polypeptide chain.

• In the process anticodons are formed• Anticodon- 3 unpaired bases of tRNA that are

complementary to mRNA•

4. GENES &

PROTI

ENS

THE RIBOSOME BINDS NEW TRNA MOLECULES AND AMINO ACIDS AS IT MOVES ALONG THE MRNA

Start codonmRNA

PROTEIN SYNTHESIS

THE PROCESS CONTINUES UNTIL THE RIBOSOME REACHES A STOP CODON.

• The sequence of bases in DNA is used as a template for mRNA.

• The codons of mRNA specify the sequence of amino acids in a protein.