Download CH. 12.3 : DNA, RNA, and Protein

CH. 12.3 :
DNA, RNA, and Protein
Section Objectives:
•Relate the concept of the gene to the
sequence of nucleotides in
DNA.
•Sequence the steps involved in
protein synthesis.
•Explain the different types of RNA
involved in protein synthesis
Genes and Proteins
• The sequence of nucleotides in DNA contain
information.
• This information is put to work through the
production of proteins.
• Proteins fold into complex, threedimensional shapes to become key cell
structures and regulators of cell
functions.
• Thus, by encoding the instructions for
making proteins, DNA controls cells.
Genes and Proteins
• You learned earlier that proteins are
polymers of amino acids.
• The sequence of nucleotides in each gene
contains information for assembling the
string of amino acids that make up a single
protein.
DNA  Proteins  Cells  Bodies
 DNA has the information to build proteins

genes
proteins
cells
bodies
DNA gets all the glory,
Proteins do all the work
Cell organization
• DNA
– DNA is in the nucleus
• genes = instructions for making proteins
– want to keep it there = protected
• “locked in the vault”
cytoplasm
nucleus
Cell organization
aa
aa
• Proteins
aa
– chains of amino acids
– made by a “protein factory” in cytoplasm
– protein factory = ribosome
cytoplasm
aa
aa
aa
aa
aa
aa
aa
build
proteins
nucleus
ribosome
Passing on DNA information: need
RNA
• RNA like DNA, is a nucleic
acid
• RNA structure differs from
DNA structure in three
ways.
Phosphate
group
Nitrogenous
base
(A, G, C, or U)
– 1. Has ribose sugar instead
of deoxyribose (DNA)
– 2. Replaces thymine (T)
with uracil (U)
– 3. Single stranded as
opposed to double
stranded DNA
Uracil (U)
Sugar
(ribose)
RNA
• RNA has a different function than DNA
• Whereas DNA provides the instructions for
protein synthesis, RNA does the actual work of
protein synthesis.
• RNAs take from DNA the instructions on how the
protein should be assembled, then—amino acid by
amino acid—RNAs assemble the protein.
RNA
• 3 types of RNA
– 1. Messenger RNA (mRNA), single, uncoiled strand
which brings instructions from DNA in the nucleus to
the site of protein synthesis.
– 2. Ribosomal RNA (rRNA), globular form, makes up the
ribosome –the construction site of proteins binds (site
of protein synthesis); binds to the mRNA and uses the
instructions to assemble the amino acids in the correct
order.
– 3. Transfer RNA (tRNA) single, folded strand that
delivers the proper amino acid to the site at the right
time
aa
Passing on DNA information
• Need to get DNA gene information
from nucleus to cytoplasm
– need a copy of DNA
– messenger RNA
aa
aa
aa
aa
aa
aa
cytoplasm
aa
aa
aa
build
proteins
mRNA
nucleus
ribosome
Protein Synthesis: 2 step process
1. Transcription 2. translation
1.Transcription: DNA -> mRNA
• In the nucleus, enzymes make an RNA copy of a
portion of a DNA strand
The main difference between transcription and DNA
replication is that transcription results in the formation of one
single-stranded RNA molecule rather than a double-stranded
DNA molecule.
2. Translation:
mRNA -> Protein
process of converting the information in a sequence of
nitrogenous bases in mRNA into a sequence of amino
acids in protein
aa
aa
From nucleus to cytoplasm
aa
aa
aa
aa
aa
transcription
DNA
mRNA
aa
aa
protein
aa
translation
trait
nucleus
cytoplasm
Transcription
• Making mRNA from DNA
• DNA strand is the
template (pattern)
– match bases
• U:A
• G:C
• Enzyme
– RNA polymerase
Matching bases of DNA & RNA
• Double stranded DNA unzips
T G G T A C A G C T A G T C A T CG T A C CG T
Matching bases of DNA & RNA
• Double stranded DNA unzips
T G G T A C A G C T A G T C A T CG T A C CG T
Matching bases of DNA & RNA
• Match RNA bases to DNA
bases on one of the DNA
strands
A
G
C
A
G
G
U
U
C
A
AG
U
C
G
A
U
A
C
A C C
RNA
polymerase
A
U
G
T G G T A C A G C T A G T C A T CG T A C CG T
U
C
Matching bases of DNA & RNA
aa
• U instead of T is matched to A
aa
aa
DNA
TACGCACATTTACGTACGCGG
aa
aa
aa
mRNA
AUGCGUGUAAAUGCAUGCGCC
aa
aa
aa
aa
ribosome
A C C A U G U C G A U C A G U A G C A U G G C A
RNA Processing
• Not all the nucleotides in the DNA of eukaryotic cells carry
instructions—or code—for making proteins.
• Genes usually contain many long noncoding nucleotide
sequences, called introns, that are scattered among the
coding sequences.
• Regions that contain information are called exons because
they are expressed.
• When mRNA is transcribed from DNA, both introns and
exons are copied.
• The introns must be removed from the mRNA before it can
function to make a protein.
• Enzymes in the nucleus cut out the intron segments and
paste the mRNA back together.
• The mRNA then leaves the nucleus and travels to the
ribosome.
RNA Processing:simplified
• Noncoding segments called introns are spliced
out ( coding segment = exons)
Genetic information written in codons is
translated into amino acid sequences
• Transfer of DNA to mRNA uses “language” of
nucleotides
– Letters: nitrogen bases of nucleotides (A,T,G,C)
– Words: codons ~triplets of bases
( ex. AGC)
– Sentences: polypeptide chain
– The codons in a gene specify the amino acid
sequence of a polypeptide
The Genetic Code
• The nucleotide
sequence transcribed
from DNA to a strand
of messenger RNA
acts as a genetic
message, the
complete information
for the building of a
protein..
• Virtually all organisms
share the same
genetic code
Translation: From mRNA to Protein
• takes place at the ribosomes in the
cytoplasm.
Involves 3 types of RNA
1. Messenger RNA (mRNA) =carries
the blueprint for construction of a protein
2. Ribosomal RNA (rRNA) =
the construction site where the protein is
made
3. Transfer RNA (tRNA) =
the truck delivering the proper amino acid to
the site at the right time
Transfer RNA molecules serve as
interpreters during translation
• In the cytoplasm, a
ribosome attaches to the
mRNA and translates its
message into a polypeptide
• The process is aided by
transfer RNAs
• Each tRNA molecule has a
triplet anticodon on one
end and an amino acid
attachment site on the
other
• Anticodon base pairs with
codon of mRNA
cytoplasm
aa
aa
aa
aa
aa
aa
proteinaa
aa
aa
aa
nucleus
ribosome
A C C A U G U C G A U C A G U A G C A U G G C A
trait
How does mRNA code for proteins
• mRNA leaves nucleus
• mRNA goes to ribosomes in cytoplasm
• Proteins built from instructions on mRNA
How?
mRNA
A C C A U G U C G A U C A GU A GC A U G GC A
aa
aa
aa
aa
aa
aa
aa
aa
DNA
How does mRNA code for
proteins?
TACGCACATTTACGTACGCGG
ribosome
AUGCGUGUAAAUGCAUGCGCC
mRNA
?
Met Arg Val Asn Ala Cys Ala
protein
aa
aa
aa
aa
aa
aa
How can you code for 20 amino acids with
only 4 DNA bases (A,U,G,C)?
aa
aa
mRNA codes for proteins in triplets
DNA
TACGCACATTTACGTACGCGG
codon
mRNA
ribosome
AUGCGUGUAAAUGCAUGCGCC
?
protein
Met Arg Val Asn Ala Cys Ala
 Codon = block of 3 mRNA bases
The Genetic code
• For ALL life!
– strongest support for a
common origin for all
life
• Code has duplicates
– several codons for each
amino acid
– mutation insurance!
 Start codon


AUG
methionine
 Stop codons

UGA, UAA, UAG
How are the codons matched to
amino acids?
DNA
TACGCACATTTACGTACGCGG
mRNA
AUGCGUGUAAAUGCAUGCGCC
codon
UAC
tRNA
amino
acid
Met
GCA
Arg
CAU
anti-codon
Val
 Anti-codon = block of 3 tRNA bases
mRNA to protein = Translation
• The working instructions  mRNA
• The reader  ribosome
• The transporter  transfer RNA (tRNA)
ribosome
mRNA
A C C A U G U C G A U C A GU A GC A U G GC A
U GG
tRNA
aa
aa
aa
U A C
tRNA
aa
A G
tRNA
aa
C
U AG
tRNA
aa
From gene to protein
aa
aa
transcription
DNA
aa
translation
protein
aa
mRNA
aa
aa
aa
ribosome
A C CA U GU C G A U C A GU A GC A U GGC A
nucleus
tRNA
cytoplasm
aa
trait
aa
cytoplasm
aa
protein
aa
aa
aa
transcription
translation
aa
aa
aa
aa
aa
aa
nucleus
trait
From gene to protein
protein
transcription
translation