Download BIO S - Chapter 13 RNA

Lesson Overview
Fermentation
Lesson Overview
13.1 RNA
Lesson Overview
Fermentation
The Role of RNA
How does RNA differ from DNA?
(1) sugar in RNA is ribose instead of deoxyribose
(2) RNA is generally single-stranded and not doublestranded
(3) RNA contains uracil (U) in place of thymine (T)
Lesson Overview
Fermentation
Comparing RNA and DNA
• RNA copies info from DNA and can take that
info OUTSIDE of the nucleus safely
• Job of RNA is to assemble amino acids into
proteins
Lesson Overview
Fermentation
Functions of RNA
The three main types of RNA are messenger
RNA (mRNA), ribosomal RNA (rRNA), and
transfer RNA (tRNA)
Lesson Overview
Fermentation
Messenger RNA
The RNA molecules
that carry copies of
DNA instructions are
known as messenger
RNA (mRNA)
Lesson Overview
Fermentation
Ribosomal RNA
ribosomal RNA (rRNA) makes up the ribosome
(where mRNA gets “read”)
Lesson Overview
Fermentation
Transfer RNA
transfer RNA (tRNA) –
carries (transfers) each
amino acid to the
ribosome
Lesson Overview
Fermentation
Transcription
•
•
•
•
Using template from DNA to make RNA
Takes place in nucleus
Makes single strand of RNA
Uracil (U) is paired up with adenine (A)
Lesson Overview
Fermentation
Transcription
THREE MAJOR STEPS:
1. INITIATION – RNA polymerase attaches to
promoter region and unwinds DNA
2. ELONGATION – RNA polymerase adds bases (A,
U, C, G) to make transcript
3. TERMINATION – transcript reaches termination
site and is released
Lesson Overview
Fermentation
Transcription
Transcription requires an enzyme, known as RNA
polymerase, that is similar to DNA
polymerase/helicase
- unwinds DNA strands and pairs up bases
http://www.wwnorton.com/college/biology/discoverbio3/core/content/index/
animations.asp
Lesson Overview
Fermentation
RNA Editing
Sometimes RNA needs to
be modified (edited)
INTRONS – portions of
RNA that are cut out and
discarded
EXONS - The remaining
pieces thjat are put back
together
Lesson Overview
Ribosomes and Protein Synthesis
Lesson Overview
13.2 Ribosomes and
Protein Synthesis
Lesson Overview
Ribosomes and Protein Synthesis
The Genetic Code
The first step in decoding genetic messages is
to transcribe a nucleotide base sequence from
DNA to RNA
The transcript contains a code for making
proteins
Lesson Overview
Ribosomes and Protein Synthesis
The Genetic Code
Proteins are made by joining amino acids together into
long chains, called polypeptides.
As many as 20 different amino acids are commonly
found in polypeptides.
Lesson Overview
Ribosomes and Protein Synthesis
The Genetic Code
Each three-letter “word” in mRNA = codon
A codon consists of three consecutive bases that
specify a single amino acid to be added to the
polypeptide chain
Lesson Overview
Ribosomes and Protein Synthesis
How to Read Codons
Because there are four
different bases in
RNA, there are 64
possible three-base
codons (4 × 4 × 4 =
64) in the genetic code
Lesson Overview
Ribosomes and Protein Synthesis
Start and Stop Codons
The codon AUG serves
as the START codon for
protein synthesis.
After AUG, mRNA is read
until it reaches one of
three different “stop”
codons
Lesson Overview
Ribosomes and Protein Synthesis
Translation
The decoding of an mRNA message into a protein is a
process known as translation
Happens at the ribosome (in cytosol/cytoplasm)
http://www.wwnorton.com/college/biology/discoverbio3/core/content/index/ani
mations.asp
http://highered.mcgrawhill.com/sites/0072556781/student_view0/chapter12/animation_quiz_2.html
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
1. ribosome attaches
to an mRNA molecule
in the cytoplasm
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
2. ribosome reads
each codon of mRNA,
and directs tRNA to
bring the specified
amino acid into the
ribosome
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
3. the ribosome then
attaches each amino
acid to the growing
chain (attaching them
together by PEPTIDE
bonds
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
4. The polypeptide chain
continues to grow until
the ribosome reaches
a “stop” codon on the
mRNA molecule
Lesson Overview
Ribosomes and Protein Synthesis
Steps in Translation
Each tRNA molecule
carries just one kind of
amino acid
In addition, each tRNA
molecule has three
unpaired bases,
collectively called the
anticodon—which is
complementary to one
mRNA codon
Lesson Overview
Ribosomes and Protein Synthesis
The Molecular Basis of Heredity
The central dogma of molecular biology is that
information is transferred from DNA to RNA to
protein