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Warm Up. The genetic code of a DNA molecule is determined by a specific sequence of A. ATP molecules C. chemical bonds B. sugar molecules D. nitrogenous bases. Protein Synthesis and Gene Expression. Why does a cell need proteins to function properly?. Time to make the

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Warm Up

The genetic code of a DNA molecule is determined by a specific sequence of

A. ATP molecules C. chemical bonds

B. sugar molecules D. nitrogenous bases


Protein Synthesis and Gene Expression


Why does a cell need proteins to function properly?

Time to make the

proteins...


SO…how does a cell make proteins anyway?


There are two important nucleic acids involved in making proteins...

1. DNA

2. RNA


Where are proteins made?

B. Ribosomes


DNA: deoxyribonucleic acid

DNA is double stranded.

Contains sugar deoxyribose.

DNA contains bases adenine, thymine, guanine, cytosine.

DNA never leaves the nucleus.

RNA: ribonucleic acid

RNA is single stranded.

Contains sugar ribose.

RNA contains bases adenine, guanine, cytosine and URACIL.

RNA can leave the nucleus.

Let’s Review DNA & RNA


Remember there are three types of RNA

  • mRNA: messenger RNA

DNA

mRNA

  • tRNA: transfer RNA.

Transcription

Amino acid

tRNA

towing

  • rRNA: ribosomal RNA

Translation


Overall process of protein synthesis

transcription

translation

mRNA

DNA

Protein


Summary of Protein Synthesis

  • DNA  mRNA  tRNA  protein

  • The process of going from DNA to mRNA is transcription.

  • The process of going from mRNA to protein is translation.


Let’s explore this in a little more detail...

First, let’s see how the message in DNA gets to the ribosomes…


DNA’s tragedy

If I could only

get out there…

I’d show them

a thing or two!

  • DNA contains volumes of information about making protein.

  • Unfortunately, DNA is too huge to leave the nucleus.

ribosomes

nucleus


How does the cell solve this problem….transcription

How do I tell

those guys what

I want them

to do?

  • That’s where mRNA comes in.

  • mRNA helps get DNA’s message out to the ribosomes...

I can help!


ATGACGATT

TACTGCTAA

First, DNA unzips itself...

  • DNA unzips itself, exposing free nitrogen bases.


ATGACGATT

TACTGCTAA

First, DNA unzips itself...

  • DNA unzips itself, exposing free nitrogen bases.


ATGACGATT

TACTGCTAA

First, DNA unzips itself...

  • DNA unzips itself, exposing free nitrogen bases.


ATGACGATT

TACTGCTAA

First, DNA unzips itself...

  • DNA unzips itself, exposing free nitrogen bases.


ATGACGATT

TACTGCTAA

First, DNA unzips itself...

  • DNA unzips itself, exposing free nitrogen bases.


IV. Transcription

  • The process of going DNA to mRNA


IV. Transcription

b. The steps of transcription:

1. First DNA unzips itself along the

segment of code needed for a certain

protein.

2. mRNA is made by forming

complementary bases on the

unzipped portion of DNA.


IV. Transcription

b. The steps of transcription:

3. DNA’s code is copied into groups of

3 bases at a time called a codon.

4. Each codon codes for 1 amino acid.

5. Once the mRNA strand is

transcribed, it can leave the nucleus

to find a ribosome to carry out the

next step.


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion


U

ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion


U

ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UA


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UA


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UAC


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UAC


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACU


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACU


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACUG


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACUG


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACUGC


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACUGC


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACUGCU


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACUGCU


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACUGCUA


ATGACGATT

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complimentary fashion

UACUGCUA


ATGACGATT

UACUGCUAA

Next, mRNA is made...

  • mRNA is made from the DNA template

  • mRNA matches with free DNA nitrogen bases in a complementary fashion


Some additional notes about making mRNA…

  • DNA contains many non-coding regions, also known as “junk DNA”

  • RNA is not made from the junk DNA


UACUGCUAA

mRNA leaves the nucleus...

I hope he can

tell them what

to do!

  • DNA’s code is copied to mRNA in three letter groups called codons.

  • After mRNA is made from the DNA template, it is ready to leave the nucleus.


UACUGCUAA

The next step...Translation

mRNA meets the Ribosomes!

(No, it’s not a new sitcom on FOX…)


I have a message

for you! It’s

from DNA!

UACUGCUAA

It’s always

something!

mRNA tries to talk to the ribosomes…

  • mRNA leaves the nucleus and travels to the cytoplasm, where the ribosomes are located.

What does

he want now?

Once there, mRNA

meets up with the

ribosomes


Why don’t they

get it???

@%$!!

UACUGCUAA

We need a

translator!

mRNA tries to talk to the ribosomes…but is unsuccessful.

Why can’t we tell

what he’s saying?

  • However, the ribosomes cannot understand the message mRNA is carrying.


Tyrosine

UACUGCUAA

AUG

Where is that

translator?

tRNA Saves the Day!

We won’t work until

we know what to do!

Looks like trouble

for this cell…

I’d better help!

The boss will NOT

be happy about

this...

Now the cell can make a protein!


tRNA: Transfer RNA

  • Chemically, tRNA is clover-leaf shaped.

  • At one end, it carries an amino acid (like a tow truck).

  • At the other end, it has a three letter code known as an anticodon.

Tyrosine

AUG


UACUGCUAA

Anticodon? What’s that?

Tyrosine

  • This anticodon is the complement to the codons contained within mRNA.

  • Can you find the mRNA complement to the anticodon on tRNA?

AUG


Some notes about Amino Acids

  • There are 20 known amino acids present in living things.

  • How is it possible to get a group of four letters to code for 20 things?

  • Put them into groups of three…

    • 43 = 64 codes

Number of members in a group of nitrogen bases

Number of nitrogen bases


What’s a codon, anyway?

  • Here is what a codon looks like. It is a sequence of 3 bases.

  • How we determine what amino acid each codon codes for must be read off of a codon chart.

  • This is also known as the genetic code.


U

C

A

G

U

Phenylalanine

Phenylalanine

Leucine

Leucine

Serine

Serine

Serine

Serine

Tyrosine

Tyrosine

Stop

Stop

Cysteine

Cysteine

Stop

Tryptophan

U

C

A

G

Second Base

C

Leucine

Leucine

Leucine

Leucine

Proline

Proline

Proline

Proline

Histidine

Histidine

Glutamine

Glutamine

Arginine

Arginine

Arginine

Arginine

UCAG

First

Base

Third

Base

A

Isoleucine

Isoleucine

Isoleucine

Methionine

Threonine

Threonine

Threonine

Threonine

Asparagine

Asparagine

Lysine

Lysine

Serine

Serine

Arginine

Arginine

UCAG

G

Valine

Valine

Valine

Valine

Alanine

Alanine

Alanine

Alanine

Aspartic Acid

Aspartic Acid

Glutamic Acid

Glutamic Acid

Glycine

Glycine

Glycine

Glycine

UCAG

Codon chart


Other Codon Charts


Reading a Codon Chart

  • It is possible for some amino acids to have more than one codon.

  • There are three stop codons…they are UAA, UGA and UAG.

  • There is also one START codon…AUG.


Methionine

AUGUGCUAA

UAC

How a Translator works…

  • First, the anticodons on tRNA meet up with the mRNA start codon (AUG) at the ribosome.

  • Next, another tRNA meets up with it’s corresponding mRNA.

  • Each tRNA carries an amino acid.


Methionine

AUGUGCUAA

UAC

How a Translator works…

  • Once two amino acids are made, a bond forms between them.

  • This process continues until a stop codon on mRNA is reached.


UACUGCUAA

Here’s the process…animated!

Note: this is a really basic representation of this process!


UACUGCUAA

Here’s the process…animated!


UACUGCUAA

AUG

tyrosine

Here’s the process…animated!


UACUGCUAA

AUG

tyrosine

Here’s the process…animated!


UACUGCUAA

Here’s the process…animated!

tyrosine


UACUGCUAA

ACG

threonine

Here’s the process…animated!

tyrosine


UACUGCUAA

ACG

threonine

Here’s the process…animated!

tyrosine


UACUGCUAA

Here’s the process…animated!

tyrosine

threonine


UACUGCUAA

Here’s the process…animated!

tyrosine

threonine


UACUGCUAA

AUU

isoleucine

Here’s the process…animated!

tyrosine

threonine


UACUGCUAA

AUU

isoleucine

Here’s the process…animated!

tyrosine

threonine


UACUGCUAA

Here’s the process…animated!

tyrosine

threonine

isoleucine


UACUGCUAA

Here’s the process…animated!

tyrosine

threonine

isoleucine


UACUGCUAA

Here’s the process…animated!

tyrosine

threonine

isoleucine


UACUGCUAA

Here’s the process…animated!

tyrosine

threonine

isoleucine


UACUGCUAA

Here’s the process…animated!

tyrosine

threonine

isoleucine


Animation of translation

Click to automatically start animation.


G

G

G

A

A

A

C

C

C

C

U

U

U

U

U

Nucleus


This is a ribosome.

G

G

G

A

A

A

C

C

C

C

U

U

U

U

U

Single Messenger RNA Strand


Met

U

C

U

G

G

G

A

A

A

C

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C

A

U

U

U

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U

tRNA

Single Messenger RNA Strand


Arg

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U

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Arg

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U

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Arg

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Arg

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Arg

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Single Messenger RNA Strand


Arg

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U

U

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U

U

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tRNA

tRNA

Single Messenger RNA Strand


Arg

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Single Messenger RNA Strand


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U

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U

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tRNA

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Single Messenger RNA Strand


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Single Messenger RNA Strand


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Single Messenger RNA Strand


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Single Messenger RNA Strand


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Single Messenger RNA Strand


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Single Messenger RNA Strand


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G

G

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tRNA

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Single Messenger RNA Strand


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Single Messenger RNA Strand


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Single Messenger RNA Strand


Gly

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Single Messenger RNA Strand


Gly

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U

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G

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Single Messenger RNA Strand


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Single Messenger RNA Strand


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Single Messenger RNA Strand


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tRNA

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Single Messenger RNA Strand


Gly

Met

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U

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G

G

G

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U

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tRNA

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Single Messenger RNA Strand


Gly

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U

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G

G

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Single Messenger RNA Strand


Arg

Lys

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U

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Single Messenger RNA Strand


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Single Messenger RNA Strand


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G

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A

A

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tRNA

tRNA

Single Messenger RNA Strand


Arg

Lys

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U

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Single Messenger RNA Strand


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Single Messenger RNA Strand


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Single Messenger RNA Strand


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tRNA

tRNA

tRNA

Single Messenger RNA Strand


Gly

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Lys

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G

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A

A

A

C

C

C

C

A

A

A

U

U

U

U

U

tRNA

tRNA

Single Messenger RNA Strand


Gly

Met

Lys

Arg

G

G

G

G

G

G

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A

A

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C

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A

A

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U

U

U

U

U

tRNA

tRNA

Single Messenger RNA Strand


Gly

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Lys

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G

G

G

G

G

G

A

A

A

C

C

C

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A

A

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U

U

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tRNA

Single Messenger RNA Strand


Gly

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Lys

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G

G

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U

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tRNA

Single Messenger RNA Strand


Lys

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A

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A

A

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U

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Single Messenger RNA Strand


Lys

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Gly

G

G

G

G

G

G

A

A

A

C

C

C

C

A

A

A

U

U

U

U

U

tRNA

tRNA

Single Messenger RNA Strand


Lys

Gly

Arg

Met

G

G

G

A

A

A

C

C

C

C

A

A

A

U

U

U

U

U

tRNA

Single Messenger RNA Strand


Lys

Gly

Arg

Met

G

G

G

A

A

A

C

C

C

C

A

A

A

U

U

U

U

U

tRNA


Lys

Gly

Arg

Met

G

G

G

A

A

A

C

C

C

C

A

A

A

U

U

U

U

U

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

A

A

A

U

U

U

U

U

tRNA

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

U

U

U

U

U

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

U

U

U

U

U

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

U

U

U

U

U

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

U

U

U

U

U

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

U

U

U

U

U

tRNA


Lys

Gly

Arg

Met

Stop

U

C

U

G

G

G

A

A

A

C

C

C

C

A

U

U

U

U

U

tRNA


STOP

How Does it Know When to Quit?

  • This process continues until a stop or a termination codon (found on mRNA) is reached.

  • There are three stop codons: UGA, UAA and UAG.


Regulation of Transcription and Translation

  • Think about your house, do you keep all the lights on ALL the time in every room??

  • Gene expression is a regulated process where genes can be turned on and off as needed due to environmental factors.


In summary…

  • DNA contains the information needed to make proteins.

  • However, DNA is too large to leave the nucleus.

  • RNA acts as a set of working instructions for ribosomes to make proteins.

  • This process is also known as gene expression.

  • Gene expression is a regulated process.


  • Central Dogma Song


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