Download Transcription, Transcription and Mutations

DNA
Transcription
and Translation
Sections 12.3 and 12.4
DNA vs. RNA
DNA
RNA
Structure:
Sugar:
Bases:
DNA example strand: TACGA
Complimentary:
TACGA
Gene
 Segment
of DNA that codes
for a protein
 The Central Dogma of
Biology:
 DNA
codes for RNA and RNA
makes protein (the synthesis
of)
One Gene – One Enzyme
 Beadle
and Tatum’s experiment showed that
one gene codes for one polypeptide
 polypeptide - a chain of covalently bonded
amino acids.
 (proteins are made of one or more
polypeptides)
RNA
RNA
stands for:
 Ribonucleic
RNA
acid
is found:
 Nucleus
and Cytoplasm
Do Now!! 
 1. What is a protein made of?
 2. Explain the importance of the central dogma.
 3. What is the purpose of RNA?
Objectives
 To compare and contrast DNA and RNA
 To identify the steps of transcription
 To define the enzymes involved
RNA Structure
 Like
DNA, RNA is made up of subunits
called _____________, which are
made of three parts:
 Sugar
(ribose)
 Phosphate
 Nitrogen Base
RNA’s Nitrogen Bases
 Adenine
(A)
 Cytosine (C)
 Guanine (G)
 Uracil (U)
There are 3 types of RNA:

Messenger RNA (mRNA) –
linear, brings genetic code
from DNA to ribosome to
make protein

Transfer RNA (tRNA) –
clover-like segments of RNA
nucleotides that transport
amino acids to the ribosomes

Ribosomal RNA (rRNA) –
helps give ribosome its
structure
All RNA is …
 Single
stranded
 Indefinite shape
Do Now!! 
 1. What is a protein made of?
 2. What are the three types of RNA? Where do
you think they’re all found?
 3. What is the central dogma?
Objectives
 To identify the steps of transcription
 To define the enzymes involved
 To identify the product of translation
Transcription
 First
step in making proteins
 Process of taking one gene and copying it
into mRNA:

Only individual genes are transcribed, NOT a
whole DNA molecule!
 DNA
-> RNA
 Location:

Nucleus of the cell
Steps to Transcription
 1.
An enzyme attaches
to the promoter (start
signal region) of a gene
and unwinds the DNA
 “Initiation” stage
Steps to Transcription (cont.)
 2.
Only one strand acts as a template:
 Other strand known as coding (non-template)
strand
Steps to Transcription (Cont.)
 3.
A mRNA copy is made from the DNA
template strand by RNA polymerase:


(RNA polymerase makes… RNA!)
Elongation stage
Steps to Transcription (cont.)
 4.
A mRNA copy is made
until it reaches the
termination (stop signal)
sequence

 5.
Termination stage
The two strands of DNA
rejoin.
Template vs. Non Template Strand
Transcription animation
 https://www.youtube.com/watch?v=ztPkv7w
c3yU
 https://www.youtube.com/watch?v=5MfSYnI
tYvg
Transcribe this DNA to mRNA
Do Now!! 
 Label
the
transcription
diagram!
Objectives
 To review the steps of transcription
 To define mRNA processing and identify its
importance
 To define poly-A tail and cap
Do Now!! 
 What is the central dogma?
 What is transcription?
 What are the three types of RNA?
 What is translation?
Objectives (P. 6)
 To review the steps of transcription
 To identify the purpose of RNA processing
 To list the steps of RNA processing and practice
removing introns
Objectives (P. 1 & 2)
 To define the building blocks of proteins and
how they are bonded
 To list the steps of translation
 To define a codon and practice using a codon
chart
mRNA Processing
 Scientists
found mRNA in cytoplasm was
shorter than DNA sequence
 mRNA processing: pre-mRNA to mRNA


Pre-mRNA – the original sequence of RNA
created during transcription
mRNA- result of processing (reaches the
ribosomes)
RNA Processing
Cap
What is RNA Processing?
 After
transcription, the premRNA molecule undergoes
processing:



5’ methyl cap is added
Splicing (introns removed)
Poly A tail is added to the 3’ end
Poly A Tail
RNA Processing
 In


Eukaryotes only:
Introns- non-coded sections
Exons- codes for a protein
 Before
RNA leaves the nucleus, introns are removed and
exons are spliced together
 A cap and poly A tail are added to ends of the sequence
 mRNA leaves the nucleus through the nuclear pores
Why is it necessary to add the poly A tail
and 5’ cap?
Let’s try an example…
 Original
DNA Sequence (DNA):
 5’ GTACTACATGCTATGCAT 3’
 Translate

it (RNA):
3’ CAUGAUGUACGAUACGUA 5’
 Add

the 5’ cap:
3’ CAUGAUGUACGAUACGUA 5’cap

Remove the introns “UGUA” and “AUAC”:
3’ CAUGAUGUACGAUACGUA 5’cap
3’ CAUGACGGUA 5’cap
Add a poly A tail onto the 3’ end
Poly A tail
3’ CAUGACGGUA 5’cap
Let’s practice
 Perform transcription on this DNA segment: GCTTCATACGA
 Do RNA processing and remove the introns: GAA and UGC
 How does this mRNA sequence leave the nucleus?
 Where does it go?
Do Now!!  (P. 6)
 What are the 3 parts of mRNA processing?
 Perform transcription then mRNA processing of
this DNA sequence:
5’ T A C T T A A C G A T C C G T C 3’
*introns: AUU, GGC
Objectives
 To identify the steps of translation
 To define codon and practice using a codon
chart
PROTEINS!
Proteins are made up of
amino acids!!!
 Proteins are polymers of amino acids
 Only 20 different amino acids
 BUT there are hundreds of thousands of different proteins
How is this possible?
Proteins
-made of 20 different Amino Acids
- Amino Acids bond to form polypeptide
chains
How do amino acids form these peptide
chains?
o
Peptide Bonds – Link each amino acids together to
form proteins
o
Dehydration synthesis! (lose a water molecule)
How many amino acids are in a dipeptide
chain?
How about a tripeptide chain?
How many water molecules are formed from 2
amino acids?
How many water molecules are formed from
100 amino acids?
Protein
Structure
http://www3.interscience.wiley.com:8100/legacy/college/boyer/0471661791/structure/HbMb/hbmb.htm
Translation!
 https://www.youtube.com/watch?v=h5mJbP23Buo
Translation
 Production of proteins from mRNA
 mRNA goes to the ribosomes in the cytoplasm
or the RER and produces proteins
 Main stages:
 1. Initiation
 2. Elongation
 3. Termination
Do Now!!  (P. 2)
 What is a codon?
 What amino acid does UUG code for? UGA?
 What are the 3 stages of translation?
Ribosome
 Two subunits to the ribosome (large and small)
 3 grooves on the ribosome (A, P, E)
 A: tRNA binding
site
 P: polypeptite bonding site
 E: exit site
Do Now!!  (P. 6)
 What are the 3 phases of translation?
 Label the diagram:
1.
2.
3.
1
 What happens at each
site?
2
3
Steps to Translation
Initiation:
1. mRNA leaves the nucleus and binds to a ribosome
2. The two ribosomal subunits come together at the 5’ end of
the mRNA
Do Now!!  (P. 1)
 What are the three phases of translation?
 List the 3 grooves in a ribosome.
 How many water molecules are lost when 20
amino acids are joined together? 2,000?
Steps to Translation (cont.)
Initiation (cont.):
3. Ribosome will find the start Codon (AUG) and the first
tRNA molecule will attach


This is the only tRNA that will attach to the P site (and skip the A
site)
The first amino acid is always methionine.
**Codon: group of 3 nucleotides on the messenger RNA that specifies
one amino acid (64 different codons)
Steps to Translation (Cont.)
Elongation:
 4. Amino acids attached to a tRNA molecule are brought
over to the mRNA (A site of ribosome)

This tRNA has an anticodon that matches the codon on the
mRNA strand
Anticodon:
Group of 3 unpaired
nucleotides on a tRNA
strand. (binds to mRNA
codon)
tRNA
Think-Pair-Share
 The mRNA sequence reads the following codons: What
amino acids do they stand for?




AUG
GGA
GAG
CAA
** What amino acid does the anticodon CGU stand for?***
Steps to Translation (cont.)
Elongation (cont.):
5. Peptide bond formed
between amino acids in P and A
sites
6. Ribosome shifts over


Translocation
“A” site now open for new
tRNA!
7. tRNA leaves E site and amino
acids behind
Think – Pair - Share
 Find the amino acid sequence
mRNA sequence (translation)
 AUGCGACGAAUUUAA
for the following
Do Now!!  (P. 6)
 Find the amino acid sequence
for the following
mRNA sequence (translation)
 AUGGGACGAUUUUUCCGGUUAUAG
 Which amino acid do these anti-codons
*UAC, GCU, AAA, AUC
code for?
Steps to Translation (Cont.)
Termination:
 8. The mRNA sequence continues to be read
until a stop codon is reached

What are the stop codons?
 9. The amino acids disconnect from the mRNA
sequence and a protein is formed.
Video!!
 https://www.youtube.com/watch?v=5bLEDd-
PSTQ
Do Now!!  (P. 1 & 6)
 Transcribe the following DNA sequence and process the pre-
mRNA:
 5’ TTACGGCTAGGAGTAGCCGAATTCTG 3’
 ** introns: CUC AUC
 Determine protein sequence
Mistakes in DNA
 Cells can make mistakes in replication and
transcription
 Most often these mistakes are fixed by enzymes
Causes of Mutations
 Can happen

spontaneously or by mutagens:
Mutagens: Certain chemicals or radiation that can cause
DNA damage
 Causes bases to pair incorrectly:

Proteins fold incorrectly, become unstable, or are not made
 High-energy forms of radiation, such as X rays and
gamma rays, are highly mutagenic.
Mutations
 A permanent change that
occurs in a cell’s DNA
 Three types of mutations:
1. Point mutation
2. Insertion
3. Deletion
Color-blindness
Progeria
Lewandowsky-Lutz
dysplasia
Hypertrichosis
Point Mutation
 Substitution: A change in just one base pair



Missense Mutation: amino acid is changed
Nonsense Mutation: amino acid is changed to a
stop codon
Silent Mutation: no change is made in amino
acid sequence
Normal RBC
Sickled RBC
Insertion
 Addition of one or more nucleotides
Deletion
 Removal of nucleotides

Ex: cri du chat syndrome- part of chromosome 5 is broken off
(a chromosomal mutation)
Frameshift Mutations
 Causes the reading frame
to shift to the left or the
right
 Caused by insertion and
deletion mutations
Normal: THE FAT CAT ATE THE BIG RAT
Mutated: HEF ATC ATA TET HEB IGR AT
ACGAAATACAGACAT
 Decide what type of mutation occurred:
 ACGAAATAGAGACAT
 ACAAATACAGACAT
 ACGAAATACAGGACAT
Sex Cell vs. Somatic Cell Mutations
 Mutations
that occur in sex cells are passed on
to the organism’s offspring and will be present
in every cell of the offspring
 Somatic
cell (non-sex cell) mutations are not
passed on to the next generation