Download Chapter 13 RNA and Protein Synthesis (1)

Chapter 13.1: RNA
Essential Questions
How
does RNA differ
from DNA?
How
does the cell
make RNA?
The Structure of RNA
RNA (Ribonucleic Acid)
 Single
stranded chain of
nucleotides
5
carbon sugar = ribose
 Phosphate
group
 Nitrogenous
bases
 Adenine
 Guanine
 Cytosine
 Uracil
(No Thymine)
Genes and Proteins:
Proteins = Many Amino Acids
 Proteins
and Traits
 Proteins
are involved in many cell functions
 Proteins
help determine traits.
 Gene is a segment of DNA that specifies the
amino acid sequence of a protein.
 Amino
Acid = 3 nucleotide bases
The Role of RNA = Protein Synthesis

Genes contain coded DNA instructions
 that

tell cells how to build proteins.
RNA serves as a temporary copy of DNA that
translates this code into a protein.
Comparing RNA and DNA
DNA
 Double
 Sugar
stranded
=
Deoxyribose
 Nitrogenous
base thymine
instead of uracil
RNA
 Single stranded
 Sugar
= Ribose
 Nitrogenous
base uracil
instead of
thymine
Types of RNA
From DNA to RNA to Protein
Transcription
A
gene is copied into RNA
 using
 This
an enzyme called RNA polymerase.
copy is called messenger RNA (mRNA).
 Location:
 mRNA
NUCLEUS
then leaves the nucleus
 then moves onto a ribosome in the cytoplasm.
A
ribosome (rRNA) uses mRNA, tRNA, and
amino acids to make proteins.
How Does it Work?
 RNA

Polymerase:
binds to region on
the DNA known as a
promoter, and
begins transcription.
RNA Editing (splicing)

Introns - which are not expressed

Exons - expressed genes.

Introns allow exons to be put together in various
sequences so that different mRNA sequences
can result from a single gene.
The Genetic Code




This is the language of mRNA
Based on the 4 bases of mRNA (A,C,G,U)
3 bases = 1 codon
The strand AUGAACUCU
The Genetic Code
3
nucleotide bases code for 1 Amino Acid
Example: AAA = Lysine, CGU = Arginine, UCG =
Serine, CCC = Proline
Translating the Genetic Code
Translation: mRNA  Protein
4.
Transcription: occurs in nucleus
mRNA: Nucleus  cytoplasm  ribosomes
tRNA: carry’s the amino acid to the ribosome
Ribosomes: attach amino acids together forming a
5.
Polypeptide chain grows until a stop codon is reached
1.
2.
3.
polypeptide chain
Steps in Translation (Decoding mRNA)

Start and Stop Codons
 Methionine
 There
AUG is the start codon
are 3 different stop codons
 mRNA is transcribed in the nucleus and
enters the cytoplasm for translation
Steps in Translation
1.
Ribosome attaches to mRNA
2.
Each codon of mRNA directs tRNA to bring the
specified amino acid into the ribosome
3.
One at a time, the ribosome then attaches each
amino acid to the growing chain
Steps in Translation

Each tRNA molecule has 3 unpaired bases called
the anticodon that match to the mRNA codon.

The tRNA molecule for methionine has the
anticodon UAC, which pairs with the methionine
codon, AUG.

mRNA moves across the ribosome like a conveyor
belt adding amino acids as it goes along, creating a
chain of amino acids (polypeptide)
Steps in Translation

The polypeptide chain continues to grow
until the ribosome reaches a “stop” codon
on the mRNA molecule.

When the ribosome reaches a stop codon, it
releases both the newly formed polypeptide
(protein) and the mRNA molecule,
completing the process of translation.
The Central Dogma of Molecular Biology

DNA  RNA  PROTEIN
Central Dogma of Molecular Biology