Transcript RNA and Protein Synthesis

RNA and Protein
Synthesis
Section 12–3
This section describes RNA and its role
in transcription and translation.
The Structure of RNA
List the three main differences between RNA
and DNA.
1. RNA has ribose sugar instead of deoxyribose.
2. RNA is generally single-stranded, instead of
double-stranded.
3.RNA contains uracil in place of thymine.
Types of RNA
► All types control protein synthesis in a cell
► 3 main types
- mRNA = messenger RNA
copies of instructions from DNA
- rRNA = ribosomal RNA
part of ribosomes
- tRNA = transfer RNA
transfers amino acids to ribosome
RNA
can be
Messenger RNA
also called
Ribosomal RNA
which functions to
mRNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
What is the importance of the cell’s ability to
copy a single DNA sequence into RNA?
► It
makes it possible for a single gene to
produce large numbers of RNA molecules.
POP QUIZ- Purpose of RNA
Is the following sentence true or false?
► RNA
is like a disposable copy of a DNA
segment.
► True
POP QUIZ- Types of RNA
What is the one job in which most RNA
molecules are involved?
► Most
are involved in
protein synthesis.
The Central Dogma
DNA
Transcription
mRNA
Translation
Protein
Figure 12–14 Transcription
► Transcription
= process of copying part of DNA
into a complementary strand of RNA
► run by enzyme called RNA polymerase
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
POP QUIZ- Transcription
Circle the letter of each sentence that is true about
transcription.
•
b. RNA polymerase uses one strand of DNA as a
template to assemble a strand of RNA.
•
c. RNA polymerase binds only to DNA promoters,
which have specific base sequences.
► Translation
Translation
= the decoding of an mRNA
message into a polypeptide chain (protein)
► Occurs on ribosomes
► Process:
- mRNA binds to ribosome
- tRNA brings appropriate amino acid to
ribosome
tRNA has anticodon that is complementary
to codon on mRNA; begins with specific
start codon - AUG
- peptide bonds are made between amino
acids
- assembly line continues until a stop codon
The Genetic Code
► Proteins are chains of amino acids
- 20 different amino acids
- the order of amino acids determines
properties of the protein
- codon = 3 consecutive nucleotides that
specify a single amino acid
- one amino acid can have multiple codons
start
codon
mRNA
A U G G G C U C C A U C G G C G C A U A A
codon 1
codon 2
codon 3
codon 4
codon 5
codon 6
codon 7
RNA Editing
► Many
RNA molecules from eukaryotic genes
have sections, called _____, edited out of
them before they become functional. The
remaining pieces, called, _________are
spliced together.
► Introns
► Exons
RNA Editing
What are two explanations for why some RNA
molecules are cut and spliced?
► It
makes it possible for a single gene to produce
several different forms of RNA.
►
It may play a role in evolution, making it possible
for small changes in DNA to have dramatic effects
in gene expression.
POP QUIZ- RNA Editing
Is the following sentence true or false?
► RNA editing occurs in the cytoplasm of the
cell.
► False
REVIEW - Translation
Four Major Steps
►A.
Messenger RNA is transcribed in the
nucleus then enters the cytoplasm and
attaches to a ribosome.
►B.
Transfer RNA translation begins at
AUG, the start codon. Each anti-codon
of tRNA complements a codon of
mRNA and binds a specific amino acid.
Translation Four Major Steps cont.
► C.
The polypeptides form an “assembly
line.” As the codons bind amino acids the
ribosome joins them together forming long
chains of amino acids.
► D.
Completing the Polypeptide- the process
continues until one of three stop codons is
reached.
Why bother?
► Transcription and translation keep master
plans (DNA) safe in the nucleus, while
blueprints (RNA) are sent to the worksite
(ribosomes)
► Proteins are needed to act as enzymes that
produces the color of your skin, the type of
blood cell, the rate of growth
POP QUIZ- The Genetic Code
Proteins are made by joining ________into
long chains called polypeptides.
► Amino
acids
The Genetic Code
► How
can only four bases in RNA carry
instructions for 20 different amino acids?
► The
genetic code is read three letters at a
time, so that each “word” of the coded
message is three bases long.
The Genetic Code
What is a codon?
► It
consists of three consecutive nucleotides
that specify a single amino acid that is to be
added to a polypeptide.
RNA Decoding Chart
The Genetic Code
Circle the letter of the number of possible
three-base codons.
• 4
• 12
c. 64
d. 128
The Genetic Code
Is the following sentence true or false?
•
All amino acids are specified by only one
codon.
► False
The Genetic Code
Circle the letter of the codon that serves as
the “start” codon for protein synthesis.
a.UGA
b.UAA
c. UAG
d. AUG
Translation
What occurs during the process of
translation?
► The
cell uses information from messenger
RNA to produce proteins.
Where does translation take place?
► Translation
takes place on the ribosomes.
Circle the letter of each sentence
that is true about translation.
► Before
translation occurs, messenger RNA is
transcribed from DNA in the nucleus.
►
It is the job of transfer RNA to bring the proper
amino acid into the ribosome to be attached to the
growing peptide chain.
► When
the ribosome reaches a stop codon, it
releases the newly formed polypeptide and the
mRNA molecule.
What is an anticodon?
► The
three bases on a tRNA molecule that
are complementary to one of the mRNA
codons.
The Roles of RNA and DNA
Match the roles with the molecules.
Roles
►
Master plan - DNA
►
Goes to the ribosomes in the cytoplasm - RNA
►
Blueprint – RNA
►
Remains in the nucleus - DNA
Genes and Proteins
► Many
proteins are_____, which catalyze and
regulate chemical reactions.
► Enzymes
Is the following sentence true or
false?
Genes are the keys to almost everything that
living cells do.
false