Lecture notes on Transcription and Translation Processes

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Transcript Lecture notes on Transcription and Translation Processes

Welcome to class  1/19/16 – 1/20/16
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Turn in Check for understanding (3 of them)
Warm up 16-20
Notes on RNA and Transcription process
Complete check for understanding
HomeFun: Genetic Code SkillSheet
Reminder: DNA project due Feb 1st and 2nd
RNA
DNA  RNA  Protein
DNA
Transcription
mRNA
Ribosome
Translation
Protein
Prokaryotic Cell
3
DNA  RNA  Protein
Nuclear
membrane
DNA
Transcription
Eukaryotic
Cell
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
4
Types of RNA
The three main types of RNA are:
Transfer RNA
Ribosomal RNA
Messenger RNA
Messenger RNA
 An mRNA molecule is a copy of the portion of DNA that will be
used to make a protein.
 After being made in the nucleus, mRNA travels to the
cytoplasm, the site of protein synthesis.
Ribosomal RNA
 Protein synthesis occurs on ribosomes, which are made up of
two subunits.
 Both subunits consist of several molecules of ribosomal RNA
(rRNA).
Transfer RNA
During protein synthesis, transfer RNA molecules (tRNA)
carry amino acids from the cytoplasm to the mRNA.
.
Three Types of RNA
• Messenger RNA (mRNA) carries
genetic information to the
ribosomes
• Ribosomal RNA (rRNA), along
with protein, makes up the
ribosomes
• Transfer RNA (tRNA) transfers
amino acids to the ribosomes
where proteins are synthesized
9
RNA Synthesis: Transcription
In transcription, segments of DNA serve as templates to
produce complementary mRNA molecules.
RNA Synthesis: Promoters
RNA polymerase binds only to regions of DNA that have specific
base sequences. These regions are called promoters.
G
T
A
C
A
U
RNA Processing
Nuclear
membrane
DNA
Transcription
Eukaryotic
Cell
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
RNA Synthesis: RNA Editing
New RNA molecules sometimes require a bit of editing
before they are ready to be read.
Introns are pulled out
and exons come
together.
End product is a mature
RNA molecule that
leaves the nucleus to
the cytoplasm.
Exons
Cap
Introns
Tail
RNA Processing
pre-RNA molecule
exon
intron
exon
intron
exon
intron
intron
exon
exon
splicesome
splicesome
exo
n
exon
exon
exon
Mature RNA molecule14
Check for understanding
1. Compare and contrast DNA and RNA following my chart
2. What are the 3 types of RNA? Draw each type and
describe their function
3. What is transcription? Where does it occur? Describe
step by step process and draw a picture of transcription
4. Contrast Intron and Extron
Ribosomes and Protein Synthesis
Importance of
proteins:
1. break down food to
power your muscles
2. send signals through
your brain that control
the body
3. transport nutrients
through your blood.
Proteins are building
blocks, they make up all
that you are.
Translation
• Synthesis of proteins in the
cytoplasm
• Involves the following:
1. mRNA (codons)
2. tRNA (anticodons)
3. ribosomes
4. amino acids
18
DNA  RNA  Protein
DNA
Transcription
mRNA
Ribosome
Translation
Protein
Prokaryotic Cell
19
DNA  RNA  Protein
Nuclear
membrane
DNA
Transcription
Eukaryotic
Cell
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Protein
20
The Genetic Code
RNA has four bases: adenine, cytosine, guanine, and uracil.
These bases form a “language”: A, C, G, and U.
The Genetic Code: Codons
 The genetic code is read in three-letter groupings called
codons.
 A codon is a group of three nucleotide bases in
messenger RNA that specifies a particular amino acid.
AUG
AAC
UCU
Genetic Code Table
There are 64 possible three-base codons in the genetic
code.
Reading Codons
Start at the middle of the circle with the first letter of the codon and
move outward.
CAC = Histidine
Start and Stop Codons
The methionine codon AUG serves as the “start” codon for
protein synthesis. There are three “stop” codons.
UAA, UAG,
and UGA
are “stop”
codons
AUG =
methionine =
“start” codon
Codon Chart: This rectangular chart his
on EOC EXAM, not the circle one
1. AAA is a
codon that
encoded for
what amino
acid?
2. CUA?
Translation
 Transcribed mRNA directs the translation process.
 Translation is the process that makes proteins using the
copy of the DNA code on the mRNA.
Translation: Transfer RNA
To start translation, tRNA molecules bind to mRNA codons,
carrying amino acids with them.
anticodon
Translation: The Polypeptide Assembly
The ribosome helps form a peptide bond. It breaks the bond
holding the first tRNA molecule to its amino acid.
Translation: Completing the Polypeptide
The ribosome reaches a stop codon, releasing the newly synthesized
polypeptide and the mRNA molecule, completing the process of
translation.
Roles of RNA in Translation
All three major forms of RNA—mRNA, tRNA, and rRNA—are
involved in the process of translation.
The Molecular Basis of Heredity
The central dogma of molecular biology is that information is
transferred from DNA to RNA to protein.
Gene Expression
When a gene (segment) of DNA code is used to build a protein,
scientists say that gene has been expressed.
Check for understanding
1. What is the purpose of translation? Describe the process
of translation in steps
2. Draw and label 3 types of RNAs including their structures
and functions
3. What is a codon? What is an anticodon?