Download Protein

DNA Transcription
and Translation
Sections 12.3 and 12.4
Do Now

1. What is RNA?

2. What are proteins used for in our bodies?

3. Fill in the chart below:
DNA
RNA
TACGA
TACGA
Structure
Sugar
Base
Example strand:
Complimentary:
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
The Beadle and Tatum experiment showed
that one gene codes for one enzyme.
 One gene codes for one polypeptide.
 polypeptide - a chain of covalently
bonded amino acids.
 (proteins are made of one or more
polypeptide)

Let’s make some observations
about RNA’s structure
RNA
 RNA
stands for:
 Ribonucleic
 RNA
acid
is found:
 Nucleus
and Cytoplasm
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) – long
strands of RNA nucleotides that are
formed complementary to one
strand of DNA.

Transfer RNA (tRNA) – smaller
segments of RNA nucleotides that
transport amino acids to the
ribosomes.

Ribosomal RNA (rRNA) – associates
with protein to form the ribosome.
All RNA is …

Single stranded

Many different shapes

“Cheap copy” of DNA
Do Now

1. What is a protein made of?

2. Explain the process between DNA and proteins.
Transcription

First step in making proteins

Process of taking one gene (DNA) and converting into a
mRNA strand

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
Steps to Transcription (Cont.)

2. One strand acts as a template.
Steps to Transcription (Cont.)

3. A mRNA copy is made from the DNA template strand
by RNA polymerase

4. A mRNA copy is made until it reaches the termination
(stop signal) sequence

5. The two strands of DNA rejoin.
Template vs. Non Template Strand
Transcription animation

https://www.youtube.com/watch?v=ztPkv7wc3yU
Transcribe this DNA to mRNA
mRNA Processing

Pre-mRNA – the original sequence of RNA created
during transcription

mRNA reaches the ribosomes
RNA Processing
What is RNA Processing?

After transcription the pre-mRNA molecule undergoes processing

5’ cap is added

Poly A tail is added to the 3’ end

Introns are removed.
Do Now

Label the Transcription diagram
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 activity (11.5)

http://www2.pearsonsuccessnet.com/snpapp/iText/pro
ducts/0-13-115075-8/index.html
Pg. 339

Pg. 339
Let’s an example…

Original DNA Sequence (DNA):

5’ GTACTACATGCTATGCAT 3’

Translate it (RNA):


3’ CAUGAUGUACGAUACGUA 5’
Add the 5’ cap:

3’ CAUGAUGUACGAUACGUA 5’
cap
Finish the job!

Remove the introns “UGUA” and “AUAC”:
3’ CAUGAUGUACGAUACGUA 5’
3’ CAUGACGGUA 5’
cap
Add a poly A tail onto the 3’ end
Poly A tail
3’ CAUGACGGUA 5’
cap
cap
Get a new partner!

DNA Strand of non-template strand:

5’ ATCGGTAGAGTATTTACAGATA 3’

Remove introns:

CGGUA
UUACAG
Think, Pair, Share

Take a minute think on your own, then pair with your partner, and share your
ideas!

Evolutionary, why do you think there are introns?

Where did they come from?

Why do we have them?

Remember there is NO wrong answer!
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 can this be?
Let’s compare to it to the
English language
How many letters are in the alphabet?
A,b,c,d,…
26
 How many words are there?
Miss, Ings, is, smart, ..
Almost infinite!
 Each word has a unique structure of
letters.


Similar to proteins and amino acids
Proteins- (PCFNa)
-made of 20 different Amino Acids
- Amino Acids bond to form polypeptide
chains
How do amino acids form
these peptide chains?
Peptide Bonds – Link each amino acids together to form proteins
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?
Do Now

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?
Protein
Structure
http://www3.interscience.wiley.com:8100/legacy/college/boyer/0471661791/structure/HbMb/hbmb.htm
Translation

Production of proteins from mRNA

mRNA goes to the ribosomes in the cytoplasm or the RER
and produces proteins
Steps to Translation

1. mRNA leaves the nucleus and binds to a ribosome

2. the 5’ end of mRNA binds to ribosome
Ribosome

Two subunits to the ribosome

3 grooves on the ribosome (A, P, E)

A: tRNA binding site

P: polypeptite bonding site

E: exit site
Steps to Translation (Cont.)

3. Ribosome looks for the start Codon (AUG)

Codon: group of 3 nucleotides on the messenger RNA that specifies one
amino acid (64 different codons)
Steps to Translation (Cont.)

4. Amino acids attached to a tRNA molecule and are brought over to
the mRNA.

5. 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.)

6. tRNA binds to the mRNA sequence and adds an amino acid

7. Each amino acid matches up with 1-6 tRNA molecules

8. tRNA leaves and amino acids bond together through a polypeptide bond
Think – Pair - Share

Find the amino acid sequence for the following mRNA
sequence (translation)

AUGCGACGAAUUUAA
Translation Animations

http://wwwclass.unl.edu/biochem/gp2/m_biology/animation/gene
/gene_a3.html

http://www.stolaf.edu/people/giannini/flashanimat/m
olgenetics/translation.swf
Steps to Translation (Cont.)

9. The mRNA sequence continues until a stop codon is
reached.

10. The amino acids disconnect from the mRNA
sequence and a protein is formed.
Think-Pair-Share

Get with a partner, one partner transcribes and the other translates.
Do Now

Do transcription on this DNA sequence:
CGTACGCTCCCTAGACTA
Do Translation- Remember to start the right place!
Do Now

Do transcription on this DNA sequence:
TTTTATACTGAGGGTTAACTCGT
Do Translation- Remember to start the right place!
1.
2.
3.
4.
5.
6.
1. Initiation

The two ribosomal subunits come together with the
mRNA and the first tRNA molecule which attaches to the
start codon (AUG).

This is the only tRNA that will attach to the P site.

The first amino acid is always methionine.
2. Codon Recognition

The tRNA anticodon will hydrogen bind to the mRNA
codon in the A site.
3. Bond Formation

The amino acid in the P site will form a peptide bond
with the amino acid in the A site.
4. Translocation

The tRNA's and the mRNA move down one site. The
empty tRNA is released from the exit site.
5. Repeat

This process will repeat hundreds of times.
6. Termination

Translation is terminated with the stop codon is
reached. There are three different stop codons UGA,
UAA, UAG.

The release factor recognizes the stop codon and
releases the polypeptide strand. All the factors break
apart and are reused.
Do Now

Take the following amino acid sequence, do reverse transcription and
translation (find RNA and DNA).

Methionine, Arginine, Alanine, Serine, Tryptophan, Tyrosine, Leucine,
Valine, stop

What do you notice about your DNA sequences?
Do Now

Template strand of DNA:

5’ TTACGGCTAGGAGTAGCCGAATTCTG 3’

Remove the introns: CUCAUC

Determine protein sequence
Do Now
How do cells know what
protein to make when?

Gene Regulation: ability of an organism to control
which genes are transcribed.
Controlling Transcription

Transcription factors ensure that a gene is used at the right time and
that protein are made in the right amounts

The complex structure of eukaryotic DNA also regulate transcription.
HOX Genes

Everyone develops from a zygote

Zygote undergoes mitosis

Cell differentiation: cells become specialized

Certain gene sequences determine cell differentiation


HOX Genes
Homeobox Genes (Hox Genes) are
sequences of DNA
Hox genes are responsible for the
general body pattern of most
animals.
HOX Genes

Are transcribed at specific times, and located in
specific places on the genome

Mutations:
Telephone

We are going to play the game telephone.

Every time a DNA makes a copy (spreading of a
message), mutations can happen (mistakes in a
message)
Mistakes in DNA

Cell make mistakes in replication, and transcription

Most often these mistakes are fixed

EX.
Mutations

A permanent change that occurs in a cell’s DNA is called a mutation.

Three types of mutations:

Point mutation

Insertion

Deletion
Point Mutation

Substitution: A change in just one base pair

Missense Mutation: amino acid is change

Nonsense Mutation: amino acid is changed to a stop codon
Frameshift Mutations

Causes the reading frame to shift to
the left or the right

Insertion: Addition of a nucleotide

Deletion: Removal of a nucleotide
ACGAAATACAGACAT

Decide what type of mutation occurred:

ACGAAATAGAGACAT

ACAAATACAGACAT

ACGAAATACAGGACAT
Causes of Mutations

Mutations can happen spontaneously

Mutagens: Certain chemicals or radiation that can cause
DNA damage

Causes bases to mispair and bond with the wrong base

High-energy forms of radiation, such as X rays and
gamma rays, are highly mutagenic.
Sex Cell vs. Somatic Cell
Mutations

Somatic cell mutations are not passed on to the next
generation.

Mutations that occur in sex cells are passed on to the
organism’s offspring and will be present in every cell of
the offspring
Chromosomal Mutations

Piece of chromosome can be broken off, duplicated, or
moved to another chromosome
Fragile X Syndrome

Repeat of CGG about 30 times

Causes mental and behavior impairments
Protein Folding and Stability

Substitutions also can lead to genetic disorders.

Ex. Sickle Cell Anemia (caused by a substitution
mutation)

Can change both the folding and stability of the protein
Sickle Cell Anemia
Causes of Mutations

Mutations can happen spontaneously

Mutagens: Certain chemicals or radiation that can cause
DNA damage

Causes bases to mispair and bond with the wrong base

High-energy forms of radiation, such as X rays and
gamma rays, are highly mutagenic.
Sex Cell vs. Somatic Cell
Mutations

Somatic cell mutations are not passed on to the next
generation.

Mutations that occur in sex cells are passed on to the
organism’s offspring and will be present in every cell of
the offspring