Transcript Biology 1 Notes Chapter 12 - DNA and RNA Prentice Hall pages

RNA & Protein Synthesis
Ribose
RNA
Hydrogen bonds
Uracil
Adenine
Mrs. Stewart
Biology I
Genes
 A gene is a section of the DNA sequence that codes for a
protein.
 Each unique gene has a unique sequence of bases.
 This unique sequence of bases will code for the production of
a unique protein.
 It is these proteins and combination of proteins that determine
the phenotypes for our traits.
DNA
How do we get from here,
to there?
Trait
DNA
GENE
RNA
Protein
Trait
REVIEW: Structure of RNA
 All forms of RNA have:
 Single stranded chain of
nucleotides
 RNA nucleotides
composed of:
1. Phosphate
2. Ribose sugar
3. Nitrogenous base
 4 Nitrogen bases of RNA:
1.
Guanine
2.
Cytosine
3.
Adenine
4. Uracil
Differences between DNA and RNA:
Structure
Bases- Purines
Bases Pyrimidines
Sugar
DNA
RNA
Double
Stranded
Adenine (A)
Guanine (G)
Single Stranded
Cytosine (C)
Thymine (T)
Deoxyribose
Cytosine (C)
Uracil (U)
Ribose
Adenine (A)
Guanine (G)
RNA’s JOB= Make Proteins!!
Types of RNA
1) messenger RNA (mRNA)- carries
instructions (the message) from the
DNA in the nucleus to the ribosome
Types of RNA
2) ribosomal RNA (rRNA)combines with proteins to
form the ribosome (proteins
made here)
3) transfer RNA (tRNA)transfers each amino acid to
the ribosome as it is specified
by coded messages in mRNA
during the construction of a
protein
Protein Synthesis Overview
There are two steps to making
proteins (protein synthesis):
1) Transcription (occurs in the
nucleus)
DNA RNA
2) Translation (occurs in the
cytoplasm)
RNA  protein
Transcription
occurs in
three main
steps:
Initiation:
Transcription begins when the enzyme RNA
polymerase binds to the DNA at a promoter site.
Promoters are signals in the DNA strand (a certain
sequence of bases) that indicate to the enzyme
where to bind to make RNA.
Elongation:
 The enzyme separates
the DNA strands by
breaking the hydrogen
bonds, and then uses
one strand of DNA as a
template from which
nucleotides are
assembled into a
strand of RNA.
 RNA polymerase pairs
up free floating RNA
nucleotides with DNA
template and joins the
nucleotides together to
form the backbone of
the new mRNA strand.
Termination
When mRNA hits a termination sequence, it separates
from the DNA
Transcription vs. Replication
 The main difference:
 Transcription results in one single-stranded mRNA molecule.
 Replication results in two double-stranded DNA molecules.
Practice
 DNA template
ATTCGGAGC
 DNA Complement (replication)
TAAGCCTCG
 mRNA (transcription)
UAAGCCUCG
mRNA synthesis animation
transcription animation
What is the purpose of the
genetic code in DNA?
Transcription
Adenine (DNA and RNA)
Cytosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
Nucleus
RNA
polymerase
DNA
RNA
After we transcribe the
message so it can leave the
nucleus, we then must have
a way to “read” the
message.
The Genetic Code
 The “language” of mRNA instructions is
called the genetic code.
 This code is written in a language that has
only four “letters” (A,G,C,U)
 How can a code with just 4 letters carry
instructions for 20 different amino acids?
The Genetic Code – what does
it code for?
 Proteins (polypeptides) - long chains
of amino acids that are joined
together.
There are 20 different amino acids.
The structure and function of
proteins are determined by the
order (sequence) of the amino
acids
The Genetic Code
The genetic code is read 3 letters at a time.
A codon consists of
three consecutive
nucleotides that
specify a single
amino acid that is to
be added to the
polypeptide
(protein).
The four bases (letters) of mRNA
(A, U, G, and C) are read three
letters at a time (and translated) to
determine the order in which amino
acids are added to a protein.
The
Codon
Wheel
64 different
mRNA
codons are
possible in
the genetic
code.
 More than one codon
can code for the same
amino acid
 Example: GGG,
GGU, GGA, GGC =
Glycine
 Some codons give
instructions
 Example: AUG =
start
 Example: UGA,
UAA, UAG = Stop
Cracking the Secret Code
 To decode a codon:
start at the
middle of the
circle and move
outward.
 Ex: CGA = Arginine
 Ex: GAU = Aspartic Acid
Cracking the Code
 This picture shows the amino
acid to which each of the 64
possible codons corresponds.
 To decode a codon, start at
the middle of the circle and
move outward.
 Ex: CGA
 Arginine
 Ex: GAU
 Aspartic Acid
Translation
Translation takes place on
ribosomes, in the
cytoplasm or attached to
the ER.
 rRNA and tRNA will
decode the message on
the mRNA strand to
produce a polypeptide
chain (protein).
http://www.youtube.com/wa
tch?v=5bLEDd-PSTQ
Messenger RNA (mRNA)
The mRNA that was transcribed from DNA during
transcription, leaves the cell’s nucleus and enters
the cytoplasm.
Transfer RNA (tRNA)
Transfer RNA (tRNA) molecules in the cytoplasm will bond
with a specific amino acid
Then, tRNA carries that amino acid to the ribosome
Each tRNA molecule has three unpaired bases called an
anticodon.
These bases are complementary to one codon on the mRNA
strand.
tRNA molecule
Anticodon
Translation
Initiation
 Begins when an
mRNA in the
cytoplasm
attaches to the
ribosome.
 AUG = the start
codon
 AUG =
methionine
The Polypeptide “Assembly Line”
tRNA anticodon will
temporarily bind to
the complementary
codon on the mRNA
molecule in the
ribosome.
(This binding of codon
to anticodon ensures
the correct amino
acid is being added)
Elongation
 The ribosome has two binding sites, allowing two tRNA molecules to line
up, side by side
 The ribosome forms a peptide bond between the first and second amino
acids on those tRNA molecules
 At the same time, the ribosome breaks the bond that held the first tRNA
molecule to its amino acid and releases the tRNA molecule.
The Polypeptide “Assembly Line”
The tRNA floats away, allowing the ribosome to move
down the mRNA molecule and bind another tRNA.
The ribosome
continues to move
along the mRNA,
attaching new tRNA
molecules and adding
more amino acids to
the polypeptide chain.
Termination
The process continues
until the ribosome
reaches one of the three
stop codons on the
mRNA.
Then, the ribosome
detaches from the
mRNA.
The result is a
polypeptide (protein
chain) that is ready for
use in the cell.
Practice
 DNA template
TAC GGT CCA AAC ACT
 mRNA (transcription)
AUG/CCA/GGU/UUG/UGA
 tRNA
UAC/GGU/CCA/AAC/ACU
 Amino Acid Sequence
 (translation)
Met-Pro-Gly-Leu-Stop
Computer Practice for
transcription and translation
 http://learn.genetics.utah.edu/content/begin/dna/transcribe/
 http://www.youtube.com/watch?v=Ikq9AcBcohA
All organisms use the same genetic
code (A,T,C,G).
This provides evidence that all life
on Earth evolved from a common
origin.