Download RNA and Protein Synthesis

RNA and Protein
Synthesis
Chapter 13 (M)
Information Flow
 Language
of DNA is written as a
sequence of bases
 If the bases are the letters the
genes are the sentences
 Information in DNA is made into
Protein
 RNA  carries & translates the
message in DNA to protein
 DNA RNA  Protein
Flow of information:
The “Central Dogma”

How do we move information from
DNA to proteins?
transcription
DNA
replication
translation
RNA
protein
Types of Nucleic Acid
 DNA
(Deoxyribonucleic
Acid) - transmits
genetic information
that is passed from one
generation to the nextdouble helix
 RNA (Ribonucleic Acid)
Nucleotide
 Composed
a
of
nitrogen base
 a pentose
sugar
a phosphate
group
Structure of DNA & RNA





DNA double
strands
(a) 5 carbon sugar deoxyribose
(b) phosphate group
(c) nitrogenous base
– adenine (A),
guanine (G), thymine
(T), cytosine (C)
A=T, G=C





RNA single strand
(a) 5 carbon sugar ribose
(b) phosphate group
(c) nitrogenous bases
- adenine (A),
guanine (G), uracil
(U),cytosine (C)
A=U, G=C
RNA-Ribonucleic Acid
 Single
stranded
 Ribose sugar
 Four bases Adenine,
Guanine, Cytosine &
Uracil(U)
 Uracil similar to
Thymine and pairs
with Adenine
Types of RNA
1.
2.
3.
m RNA transfers the genetic
code of DNA in the nucleus to
the ribosome in the cytoplasm
t-RNA  transfers amino
acids to the ribosome to make
proteins
r- RNA  ribosomal RNA
Transcription: DNA RNA
Construction of RNA along portions of
the DNA molecule
 Stages

 Initiation
 Elongation
 Termination
Initiation

1.
2.
DNA is double stranded and has regions
on it “Promoters” (TATA box) where
transcription starts.
DNA is unzipped, bases are exposed
“RNA Polymerase” attaches to the
promoter region ready to start making
RNA
Elongation
1.
2.
3.
RNA nucleotides pair with the
exposed DNA bases
RNA Polymerase then links the RNA
nucleotides together to form a chain
(mRNA)
As the RNA peels off the DNA chain,
DNA strands rejoins.
Termination
When the RNA Polymerase reaches a
special base sequence of DNA
(terminator) which signals the end, the
RNA Polymerase detaches from the
DNA
 Two other types of RNA – tRNA & rRNA
are made in the same way

Editing the RNA Message
RNA transcribed in the nucleus is
modified before it leaves the nucleus as
mRNA to be translated.
 mRNA

 Introns
noncoding regions
 Exons the parts that remain & will be
translated, or "expressed

RNA Splicing joining of the exons after
the introns are removed
RNA Splicing
Ribosomes and
Protein Synthesis
13.2
The Triplet Code
 DNA
stores information to make
protein  20 AAs, functional if
order is correct
 English 1000s words 
arrangement of 26 letters
 DNA Code  sequence of 3 bases
(A,T,G,C)  genetic alphabet
 Start Codon = 1, Stop Codons =3
The Triplet Code
Translation
Process by which mRNA code is
read and converted into a specific
amino acid sequence (protein)
Players:
1. Ribosomes
2. mRNA
3. tRNA

Ribosomes

Made of two subunits
 Large
p-site,& A-site
 Small m RNA binding site
t-RNA
Steps in Translation
1.
2.
3.
Initiation
Elongation
Termination
Initiation



mRNA binds to small subunit of ribosome
Initiator tRNA binds to specific start
codon on mRNA & carries the AA Met
Anticodon=UAC(tRNA)
Codon =AUG (mRNA)
Large subunit binds to the small
functional ribosome
Initiation
Initiation
Elongation
Codon Recognition: incoming tRNA with
an AA attached pairs with the mRNA
codon on the “A-site”
 Peptide bond formation: a bond is formed
between the AA or peptide on “P-site” &
AA on the “A-site”
 Translocation: “P-site” tRNA moves out.
“A-site” tRNA w/polypeptide chain moves
to “P-site”

Ribosome with mRNA and tRNA
Figure 17.18 The elongation cycle of translation
Termination
Process continues till a “stop codon” is
reached
 Process is terminated.
 Stop Codons: UAA, UAG, UGA

Termination
Mutations in Genes
Ch 13.3
Mutation
A change in the nucleotide sequence of
DNA
 Can involve large sections of the DNA or
just a single nucleotide pair (Point
mutations)
 Types

 Base
Substitution
 Base Deletion
 Base Insertion
Base Substitution
Base Substitution
Base Insertion/Deletion
Is usually more disastrous than the
effects of base substitutions
 RNA is read as a series of triplets, thus
adding or removing nucleotides will
affect all nucleotides downstream.
 Will result in a different , non working
protein

Causes of Mutations
 May
occur when errors are made
during DNA replication
 When errors are made during
chromosome crossovers in meiosis.
 Physical or chemical agents 
mutagens
Mutagen
Physical mutagen  high-energy
radiation X-rays and ultraviolet light.
 Chemical mutagen  chemicals that are
similar to normal DNA bases but cause
incorrect base-pairing when
incorporated into DNA.

Mutations: Good or Bad
Harmful
 Cancers
 Sickle cell disease
Beneficial
 Chemical resistance
 Plants  polyploidy
Mutations: Good or Bad
Mutations  genetic
diversity
 May be beneficial
tiger swallowtail
butterfly mutations
cause a change in color
predators confuse it
with w/ black swallowtail
which is poisonous and
avoid it
