Molecular Biology: From DNA to Protein (Part II) Transcription • Purpose and sub-cellular compartment. • Steps of transcription and the bio-molecules involved. • Terminology: promoter and terminator DNA sequences RNA Processing in eukaryotic cells Genetic code • The language of nucleic acids: letters and words (nucleotides and codons) • Initiation and termination codons of translation Mutation • Definition, sources, impact the protein product Translation or protein synthesis • Purpose and sub-cellular compartment and its three steps. • The interpreter the language of nucleic acids into the language of proteins Use the genetic code table to translate a sequence of codons into a sequence of amino acids and the reverse as well as the sequence of normal and mutated proteins
34
Embed
Molecular Biology: From DNA to Protein (Part II ...
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Molecular Biology: From DNA to Protein (Part II) Transcription • Purpose and sub-cellular compartment. • Steps of transcription and the bio-molecules involved. • Terminology: promoter and terminator DNA sequences RNA Processing in eukaryotic cells Genetic code • The language of nucleic acids: letters and words (nucleotides and codons) • Initiation and termination codons of translation Mutation • Definition, sources, impact the protein product Translation or protein synthesis • Purpose and sub-cellular compartment and its three steps. • The interpreter the language of nucleic acids into the language of proteins Use the genetic code table to translate a sequence of codons into a sequence of
amino acids and the reverse as well as the sequence of normal and mutated proteins
How DNA directs the functions of the cell?
• RNA Structure • Transcription process, steps, and molecular participants • Translation Process and Steps and molecular participants
Key Hydrogen atom Carbon atom Nitrogen atom Oxygen atom Phosphorus atom
Nitrogenous base (A, G, C, or
U) Phosphate group
O
O–
O O CH2
H C
C
C
C N
C
N
H
H
O
O
C
O
O
H
C H H
OH
C
H
Uracil (U)
Sugar (ribose)
P
Transcription of a gene 1. DNA: double –stranded 2. Enzyme: RNA Polymerase 3. Monomers: RNA ribonucleotides 4. Steps:
• Proteins discrete structural and functional regions called domains.
• Different exons code for different domains of a protein.
THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN
• The information carried by sequence of DNA bases constitutes an organism’s genotype
• The DNA genotype is expressed as proteins, which provide the molecular basis for the phenotype
Genetic information written in a code that is translated into amino acid sequences
The “words” of the DNA “language” are triplets of bases (3 bases long) called codons
Each codons in a gene specify one amino acid
sequence of the polypeptide
Protein synthesis Translation is the RNA–directed synthesis of a
polypeptide Translation of the language of nucleic acids into
the language of proteins (amino acids) One codon ------ one amino acid
DNA molecule
Gene 1
Gene 2
Gene 3
DNA strand (template)
3′
TRANSCRIPTION
Codon
mRNA
TRANSLATION
Protein
Amino acid
3′ 5′
5′
From the language of DNA to the language of proteins
The genetic code is the Rosetta stone of life Nearly all organisms use exactly the same genetic code
Figure 10.8A
UUC UGU UGC UGA Stop
Met or start
Phe
Leu
Leu
Ile
Val Ala
Thr
Pro
Ser
Asn
Lys
His
Gln
Asp
Glu
Ser
Arg
Arg
Gly
Cys Tyr
G
A
C
U
U C A G
Second base
Firs
t bas
e
UUA
UUU
CUC CUU
CUG CUA
AUC AUU
AUG
AUA
GUC GUU
GUG
GUA
UCC UCU
UCG
UCA
CCC CCU
CCG CCA
ACC ACU
ACC ACA
GCC GCU
GCG
GCA
UAC UAU
UAG Stop
UAA Stop
CAC CAU
CAG CAA
AAC AAU
AAG AAA
GAC GAU
GAG
GAA
UGG Trp
CGC CGU
CGG CGA
AGC AGU
AGG AGA
GGC GGU
GGG
GGA
U
C
A
G
U
C
A
G
U
C
A
G U
C
A
G
In-class activity/Genetic code Use the genetic code table to answer the following questions 1. How many codons are there for leu (leucine)? 2. How many codons are there for Met (Methionine)? 3. How many codons are there for Phe (phenylalanine)? Draw a conclusion about the number of codons for amino acids. 4. How many “stop” codons are there? Answer the following questions using this genetic code: 5’-AUGACCCCUUUGUUAUACUAA-3’ 5. How long is this message in nucleotides? 6. Is this the information present in DNA or in mRNA? Explain your answer . 7. Write down the sequence of amino acids coded for by the above stretch of nucleotides. how long is this polypeptide? .
Mutation/ In- class
1. For amino acids with redundant codons, which nucleotide position(s) are always the same, i.e conserved? (marked next to the genetic code table) . 2. Which amino acid does UUA code for? . 3. Does a mutation that changes the codon UUA into a UUG change the amino acid sequence at the protein level? . 4. Does a DNA mutation changing the codon UUA into a UCA change the amino acid sequence at the protein level? . 5. What impact would a change of the codon UUA into a UAA have at the translational level? . In Question 3, the mutation is a . In Question 4, the mutation is a . In Question 5, the mutation is a .
Nucleotide substitutions cause small changes in protein structure
Section 7.7
Wild type = original nucleotide sequence
Substitution = changed nucleotide(s)
Table 7.2
T A B L E 7.2 Types of Mutations Type Illustration Original Sentence
THE ONE BIG FLY HAD ONE RED EYE
Substitution (missense)
THQ ONE BIG FLY HAD ONE RED EYE
Nonsense THE ONE BIG Insertion THE ONE BIG WET FLY HAD ONE RED EYE Insertion (frameshift)
THE ONE QBI GFL YHA DON ERE DEY
Deletion THE ONE BIG HAD ONE RED EYE Expanding repeat
Generation 1: THE ONE BIG FLY HAD ONE RED EYE Generation 2: THE ONE BIG FLY FLY FLY HAD ONE RED EYE Generation 3: THE ONE BIG FLY FLY FLY FLY FLY FLY HAD ONE RED EYE
Only one codon is altered, so only one amino acid in the protein will be affected.
“Frameshift” mutations cause large changes in protein structure
Section 7.7
Insertion of one nucleotide changes every codon after the insertion.
Table 7.2
T A B L E 7.2 Types of Mutations Type Illustration Original Sentence
THE ONE BIG FLY HAD ONE RED EYE
Substitution (missense)
THQ ONE BIG FLY HAD ONE RED EYE
Nonsense THE ONE BIG Insertion THE ONE BIG WET FLY HAD ONE RED EYE Insertion (frameshift)
THE ONE QBI GFL YHA DON ERE DEY
Deletion THE ONE BIG HAD ONE RED EYE Expanding repeat
Generation 1: THE ONE BIG FLY HAD ONE RED EYE Generation 2: THE ONE BIG FLY FLY FLY HAD ONE RED EYE Generation 3: THE ONE BIG FLY FLY FLY FLY FLY FLY HAD ONE RED EYE
A codon start codon within the mRNA message marks the translation initiation and a stop codon marks the end of translation
Start of genetic message
End
Figure 10.13A
Transfer RNA molecules serve as interpreters during translation
- Each tRNA molecule is a folded molecule bearing a base triplet called an anticodon on one end - A specific amino acid is attached to the other end
Amino acid attachment site
Anticodon
Amino acid attachment site
Hydrogen bond
RNA polynucleotide chain
Anticodon Figure 10.11A
Steps of protein Synthesis 1. Initiation a. binding of mRNA to small ribosomal subunit b. binding of Met-tRNA to AUG on mRNA c. Binding of large ribosomal subunit
2. Elongation a. binding of a second tRNA to next codon b. formation of peptide bond between Met and the second
amino acid c. sliding of ribosome by one codon Amino acids are added to the growing polypeptide chain until a
stop codon is reached.
3. Termination Disassembly of the protein synthesis machinery