Download DNA vs. RNA - WordPress.com

12-3 Protein Synthesis
1
DNA
vs.
Double stranded
 Sugar = deoxyribose
 Thymine (no Uracil)

Stays in nucleus
 One type







Same copy in the cell all 
the time
RNA
Single stranded
Sugar = ribose
Uracil (instead of
Thymine)
Nucleus & cytoplasm
3 types (mRNA, tRNA,
rRNA)
Disposable copies
2
3
Ribose vs. Deoxyribose
4
RNA
 many
functions but mostly just
protein synthesis
 three
main types of RNA: messenger
RNA, ribosomal RNA, and transfer
RNA
5
Types of RNA
6
mRNA
RNA molecules that carry copies of the
DNA instructions = mRNA
 messenger RNA (mRNA) = serve as
“messengers” from DNA to the rest of the
cell

7
rRNA

Ribosomes are made up of several dozen
proteins, as well as a form of RNA known
as ribosomal RNA (rRNA).
8
tRNA

During the construction of a protein, a third
type of RNA molecule transfers each amino
acid to the ribosome
– as specified by coded
messages in mRNA.

These RNA molecules
are known as
transfer RNA (tRNA).
9
Transcription & Translation
10
Transcription (DNA  mRNA)







RNA molecules are produced by copying part of the
nucleotide sequence of DNA into a
complementary sequence in RNA
required enzyme = RNA polymerase
RNA polymerase binds to DNA (in nucleus)
separates the DNA strands
RNA polymerase then uses one strand of DNA as a
template
nucleotides are assembled into a strand of mRNA
Transcription Animation
11
12
13
Where does RNA start?
enzyme will bind only to regions of DNA
known as promoters
 promoters are signals in DNA that
indicate to the enzyme where to bind to
make RNA (“start sequence”).
 Similar signals in DNA cause transcription
to stop when the new RNA molecule is
completed.

14
RNA Editing
Intron = intervening sequence of DNA; does
not code for a protein
 Exon = expressed sequence of DNA; codes
for a protein
 When RNA molecules are formed, both the
introns and the exons are copied from the
DNA
 introns are cut out of RNA molecules while
they are still in the nucleus
 exons are then spliced back together to form
the final mRNA

15
16
The Genetic Code
Proteins = long chains of amino acids
(polypeptides)
 polypeptide = combination of any or all of
the 20 different amino acids
 properties of proteins are determined
by the order in which different amino acids
are joined together to produce
polypeptides

17
The “language” of mRNA instructions is
called the genetic code
 RNA contains four different bases: A, U, C,
and G
 Letters read “3” at a time = codon
 Codon = a group of three nucleotides on
messenger RNA that specify a particular
amino acid.

18
19
Translation
(mRNA tRNA amino acid chain)
 Occurs
at the Ribosome
 mRNA = instructions for the order
of the amino acid sequence
 Ribosome = reads the instructions
of the mRNA
20
21
Steps of Translation
 mRNA
is released from the nucleus 
enters cytoplasm
 mRNA attaches to the ribosome
 mRNA codons move through the
ribosome proper amino acid brought by
tRNA
 Amino acids are bound together 
polypeptide chain
22

Each tRNA carries only one type of amino
acid

The three bases on tRNA = anticodon
(complementary to mRNA)
23
24
The ribosome forms peptide bonds
between the neighboring amino acids
 It also breaks the bonds between tRNA and
the amino acids
 Translation ends when a “stop” codon is
reached

25
26
 Translation
Animation
27
What amino acids are made?
Use the mRNA strand on the Genetic Code
Chart
 DNA: TAC AAA CAC GGA CCA ACT
(antisense strand)
 mRNA: AUG UUU GUG CCU GGU UGA
 tRNA: UAC AAA CAC GGA CCA ACU
 Amino acids: Methionine – Phenylalanine –
Valine - Proline - Glycine - STOP

28
29