Chapter 13
(Pgs 360-389 Miller and Levine Biology
text)
http://www.youtube.com/watch?v=suNsV0cT6c
MITOSIS
AND
MEIOSIS
DNA mRNA tRNA PROTEIN
Transcription
Translation

DNA…
• Nucleotides = deoxyribose sugar
• Double helix structure
• Stays inside nucleus

RNA…
• Nuleotides = ribose sugar
• Single-strand structure
• Located both inside and outside of nucleus
• Uracil instead of thymine
A Closer Look at RNA:
•Contains ribose sugar instead of
deoxyribose sugar
•Single stranded
•The nucleotide uracil replaces thymine
3 Types of RNA
•
Messenger RNA = mRNA
-Carries genetic coded message sequence from DNA, in the nucleus to the
ribosome in the cytoplasm.
• Ribosomal RNA = rRNA
- One of components of the
ribosome, rRNA associates with protein to form the ribosome. There are
1000’s of ribosomes/cell.
-Ribosomal RNA (rRNA) is part of the ribosome. rRNA consists of two subunits
that are made up of several ribosomal RNA. Proteins are assembled on the
ribosomes.
•
Transfer RNA = tRNA
- Transfer RNA (tRNA) transfers each amino acid to the ribosome as it is
specified by the coded messages in mRNA. Transfer RNA carries amino acids
to the ribosome and matches them to the coded mRNA message. There is one
specific tRNA for each amino acid.
http://www.youtube.com/watch?v=NJxobgkPEAo
 mRNA
– stands for messenger RNA
• it is the copy of the DNA message for making a
protein
• Occurs in the nucleus
• Promoter region on DNA marks where
transcription should start and terminator region
marks where it should stop
Basic Principles of Transcription
and Translation
• Transcription
– Is the synthesis of RNA under the direction of
DNA
– Produces messenger RNA (mRNA)
– In transcription, segments of DNA serve as
templates to produce complementary RNA
molecules.
– In eukaryotes, RNA is produced in the cell’s
nucleus and then moves to the cytoplasm.
Transcription requires an enzyme
known as RNA polymerase.
RNA polymerase
• Binds to DNA during transcription
and separates the DNA strands.
• It uses one strand of DNA as a
template to create a complementary
strand of RNA.
• RNA polymerase only binds to
promoters, which are regions of DNA that
have specific base sequences.
• Before it becomes mRNA, it is called premRNA. Pre-mRNA molecules have bits
and pieces cut out of them before they
can go into action. The portions that are
cut out are called introns.
• The remaining pieces, known as exons,
are then spliced back together to form
the final mRNA.
1.
2.
Introns-DNA sequences present in
some genes that transcribed BUT are
removed during processing and
therefore are not present in mRNA.
Exons-DNA sequence that are
transcribed and joined to other exons
during mRNA processing and are
translated into amino acid sequence
of a protein
•In eukaryotes
–RNA transcripts are modified before becoming true
mRNA
Nuclear
envelope
DNA
TRANSCRIPTION
Pre-mRNA
RNA PROCESSING
mRNA
Ribosome
TRANSLATION
Polypeptide
(b) Eukaryotic cell. The nucleus provides a separate
compartment for transcription. The original RNA
transcript, called pre-mRNA, is processed in various
ways before leaving the nucleus as mRNA.
 No
T (thymine) so when it reads the
nucleotide A on DNA it matches it with
____?
 DNA
contains all the information for your
traits – the genes
 These genes are blueprints and need to
remain safe – kept inside the nucleus
 Copies can be made though – a
messenger
 http://www.youtube.com/watch?v=NJxobgk
PEAo
 Proteins
are made by joining amino acids
together into long chains called
polypeptides.
 20 different amino acids are commonly
found in polypeptides.
 RNA contains four different bases:
 Adenine, cytosine, guanine, and uracil.
 The
genetic code is read three letters at a
time, so that each words is three bases
long and corresponds to a single amino
acid.
 Each three letter “word” is called a
codon.
 Most
amino acids can be specified by
more than one codon.
 UUA, UUG, CUU, CUC, CUA, and CUG all
code for leucine.
 It’s time to code! Look at page 367 of
your book and follow the steps in figure
13-6.
 The
start (initiation) codon for protein
synthesis is AUG, which codes for the
amino acid, methionine.
 mRNA continues to be read, three bases
at a time, until it reaches a stop codon.
This ends translation and the polypeptide
is complete.
 If
given the following DNA sequence,
determine the mRNA sequence
transcribed for this gene. Then
determine the amino acid sequence of
the polypeptide using the codon chart.
 DNA: T A C A A G T C C A C A A T C
 DNA: T
ACGACAAGTCCACAATC
 mRNA: A U G C U G U U C AGG UG UU A G
 Leucine-phenylalanine-arginine-cysteine-
stop.
Wait, why did we stop?
STOP codons: UAA, UAG, UGA
 mRNA
gives instructions on the order in
which amino acids should be joined to
produce a polypeptide.
 Ribosomes use the sequence of codons
in mRNA to assemble amino acids into
polypeptide chains.
 Translation is the process of decoding an
mRNA message into a protein.
 Transcription
is carried on in the cell’s
nucleus.
 Translation is carried out by ribosomes
after the transcribed mRNA enters the
cell’s cytoplasm.
1. Translation begins when a ribosome
attaches to an mRNA molecule in the
cytoplasm.
2. tRNA brings the proper amino acid into
the ribosome. One at a time, the
ribosome attaches these amino acids to
the growing chain.
 Each
tRNA molecule carries just one kind
of amino acid and it contains three
unpaired bases. These are called the
anticodon.
 HOLD
UP Mrs. Wald…. WHAT?! A codon
and an anticodon? Please explain.
TRANSCRIPTION
DNA
mRNA
Ribosome
TRANSLATION
Polypeptide
Molecules of tRNA are
not all identical
Amino
acids
Polypeptide
1. Each carries a
specific amino acid
on one end
Ribosome
tRNA with
amino acid
attached
Gly
2. Each has an
anticodon on the
other end
tRNA
Anticodon
A A A
U G G U U U G G C
Codons
5
mRNA
3
 If
you are provided the codon:
AUG
The anticodon (which is located on tRNA)
is:
UAC
Great, so what’s the amino acid? Do
you use AUG or UAC?
You use the codon, so AUG, which
codes for the amino acid methionine.
 3. The
ribosome joins the amino acids in
the binding sites and tRNA floats away
from the ribosome. This creates a
peptide chain!
 4. The process continues until the
ribosome reaches one of three of the stop
condons.
 All
three forms of RNA come together
during translation.
 mRNA carries the coded message.
 tRNA delivers the correct amino acid.
 Ribosomes are composed of roughly 80
proteins and 3 or 4 rRNA molecules.
 rRNA helps hold ribosomal proteins in
place and locate the beginning of the
mRNA message.
 Proteins
have everything to do with traits!
 The central dogma of molecular biology
is that information is transferred from
DNA to RNA to protein.
 Transcribes
DNA message and carries it to
ribosome
 RNA polymerse is the enzyme that
produces it
CLICK ON
PICTURE FOR
ANIMATION ON
TRANSCRIPTION
 Once
mRNA is made it attaches to a
ribosome
 tRNA = transfer RNA and they carry amino
acids
 Amino acids are the building blocks of
proteins (remember?)
•During transcription
–The gene determines the sequence of bases along the
length of an mRNA molecule
Gene 2
DNA
molecule
Gene 1
Gene 3
DNA strand 3
A C C A A A C C G A G T
(template)
5
TRANSCRIPTION
mRNA
5
U G G U U U G G C U C A
Codon
TRANSLATION
Protein
Trp
Amino acid
Phe
Gly
Ser
3
Section 12-3
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
From the DNA sequence
complementary DNA sequence:
below,
write
TGA TTT CGG TAC GAT TAA CAA CCT CGA ATT
ACT AAA GCC ATG CTA ATT GTT GGT GCT TAA
If the top DNA strand encodes the message to make a
protein, then what will the transcribed M-RNA be:
ACU AAA GCC AUG CUA AUU GUU GGA GAU UAA
the
A tRNA molecule
–Consists of a single RNA strand that is only about
80 nucleotides long
–Is roughly L-shaped
3
A
C
C
A 5
C G
G C
C G
U G
U A
A U
A U
U C
UA
C A C AG
*
G
*
G U G U *
C
C
* *
U C
*
* G AG C
(a) Two-dimensional structure. The four base-paired regions and three
G C
U A
loops are characteristic of all tRNAs, as is the base sequence of the
* G
amino acid attachment site at the 3 end. The anticodon triplet is
A
A*
unique to each tRNA type. (The asterisks mark bases that have been
C
U
*
chemically modified, a characteristic of tRNA.)
A
G
A
Amino acid
attachment site
Anticodon
C U C
G A G
A G *
*
G
A G G
Hydrogen
bonds
Molecular Components of Translation
•A cell translates an mRNA message into protein
–With the help of transfer RNA (tRNA)
http://highered.mcgrawhill.com/sites/dl/free/0072437316/12006
0/ravenanimation.html
Molecular Components of
Transcription
• RNA synthesis
– Is catalyzed by RNA polymerase, which pries
the DNA strands apart and hooks together the
RNA nucleotides
– Follows the same base-pairing rules as DNA,
except that in RNA, uracil substitutes for
thymine
DNA
Nucleotide
Deoxyribose
RNA
X
X
Ribose
X
Single-stranded
Double-stranded
Nitrogenous
bases
X
X
X
X
X
DNA
Thymine
RNA
X
Uracil
Template for synthesis of
nucleic acid
Double helix
Replication
Transcription
X
X
X
X
X
X
DNA
RNA
Exact Copy
X
Messenger
More Than 1
Form
Found in
Nucleus
Leaves Nucleus
X
X
X
X
X
Does not Leave
X
RNA
can be
mRNA
rRNA
also called
which functions to
Messenger
RNA
Carry instructions
from
DNA
also called
Ribosomal
RNA
tRNA
which functions to
also called
which functions to
Combine with
protein
Transfer RNA
Brings amino acids
to the ribosome
to
to make up
Ribosomes
Ribosomes