Making Proteins

This image summarizes the

processes of transcription and

translation.

What are the three stages in this process

(central dogma) and where are they in this

picture?

DNA

mRNA

tRNA

rRNA

protein

RNA• RNA (Ribonucleic Acid)

– Contains Ribose as the sugar in its sugar-phosphate backbone

• RNA has Uracil rather than Thymine as a base– Base pairs: A – UC – G

• 3 types of RNA– messenger (mRNA)– transfer (tRNA)– ribosomal (rRNA)

Two Steps to Protein Synthesis

1. Transcription: mRNA is made from a strand of DNA

2. Translation: Protein is made by a ribosome by using mRNA as the set of “instructions.”

Transcription in Prokaryotes

• DNA is transcribed into mRNA

Translationin Prokaryotes

• mRNA serves as the instructional material to make proteins

Transcriptionin Eukaryotes

• DNA is transcribed into pre-mRNA

RNA Processingin Eukaryotes

• Non-coding regions of the mRNA, called introns, are removed from the pre-mRNA.

Translationin Eukaryotes

• The mRNA with only the coding region (the exons) leaves the nucleus.

• Translation from mRNA to protein occurs in the cytoplasm.

Steps of DNA Transcription Making mRNA from DNA

1. Helicase does NOT unzip DNA at the gene of interest

2. RNA polymerase unwinds and matches RNA nucleotide bases to DNA, using one side as a template.

3. The mRNA strand is created. It now compliments the original DNA strand (G-C and A-U).

4. Ligase helps the strand of DNA to close and again.5. mRNA strand moves out of nucleus to ribosomes,

and the DNA zips up.

Key Players in TranslationrRNA = RNA that makes up a ribosome

tRNA = RNA that transfers specific amino acids

mRNA = carries the DNA message;

RNA transcribed from DNA

Codon = 3 nucleotides in a row on a strand of mRNA that code for an amino acid

Anticodon = 3 nucleotides in tRNA that base pair with the codon

Amino Acids = monomers of proteins (20 in humans)

Steps to TranslationMaking proteins from mRNA

1. Ribosomes attach to the “start” codon of mRNA (AUG), signaling the beginning of the protein chain

2. mRNA codons are matched to corresponding tRNA anticodons and appropriate amino acids are strung together.

3. Dehydration synthesis occurs between the amino acids, and they join, making a protein chain with peptide bonds in between

4. Ribosomes detach when they come across a “stop” codon (UAA, UAG, UGA). Protein synthesis is complete.

Why do you think RNA

uses the “triplet code”?

Do the math on your own or

with a neighbor.

CODON BINGO

• Fill in the Bingo Card (on page 45) with the 20 different amino acids.– Use your table on page 44 to help– Watch out for repeated amino acids!

• Wait for your teacher to begin calling out DNA letters to begin playing

Translation Activity

• You and your classmates need to discover the hidden protein in your bag.

• Follow the instructions in the bag to unlock the mystery protein.

What if a single base is changed?

What if a single base is changed?

What if a single base is changed?

Proteins

• Made up of Carbon, Hydrogen, Oxygen and Nitrogen (and some Sulfur)

• Proteins are responsible for many reactions

Types of Proteins

1. Enzymes = Catalysts that speed up the rate of a chemical reaction – Build up or break down substrate

• Fit together with its substrate like a “lock” and a “key”

– Not used up in the reaction– Work in a very specific biological range– Usually end with “-ase”

Hi sweeties, Do you remember

me?

In addition to what you know. I am a

substrate.

I am an enzyme. I am going to try to convert you.

I am now a product.

I am a glucose now.

I am a product, too. I am a fructose now.

I am completely unchanged, and

ready for some more sucrose!

I am the active site. The substrate binds

to me.

Proteins

2. Structural Proteins– Provides mechanical support to cells and

tissues

3. Transport Proteins– Transports small ions or molecules

4. Motor Proteins– Enables structures to move

Proteins

5. Hormones (signaling proteins)– Carries signals from cell-to-cell– e.g., insulin

6. Storage– Stores small molecules or ions– e.g., iron is stored in the liver in ferritin

7. Other specialized functions– Defense (immune system antibodies), – Receptor proteins (in eyes and muscles to

detect stimulus)

Proteins• Proteins monomers are called amino acids

– Peptide Bond: Bond between 2 Amino Acids:

H2O

Proteins

• A chain of amino acids are called “polypeptides”

“Many Peptides”• Polypeptides fold and twist to form a

specific shape• Two or more polypeptides form a

complete protein• These shapes

allow proteins to function

Poly peptides

Endo-membrane

System

A system of membrane organelles that are inter-related in their

function

How are the organelles of the endomembrane system inter-

related?

Take notes on the following slides as your teacher

narrates what is happening

How does this design compare to what we have already

learned about protein synthesis?

What’s up? I am

the Nucleus… what do I do for the

cell?

Do you remember me?

I’ll give you a hint: I am in

charge of making

ribosomes and the RNA used to make proteins!

Well, before we go too far, we must not

forget about me! Sometimes I’m rough and sometimes I’m smooth… no matter

what, I’m always important to protein

synthesis!

I have a bit of a complex, because I

go by several different last names.

However, my first name is always Golgi.

Which does give

me a complex as

well…

I am a ribosomal subunit… soon to

become a ribosome.

Follow me as I travel to the E.R.

Now let’s look at some more detailed animations!

http://www.stolaf.edu/people/giannini/flashanimat/cellstructures/dna.swf

http://www.johnkyrk.com/er.html

How are proteins created by the “free” ribosomes differ in

destination from the proteins created by the “attached”

ribosomes of the ER?

Attached Ribosomes: They make proteins that are either 1) secreted out of the cell

2) attached to the plasma membrane 3) stays enclosed in a membrane to function

as another organelle, such as a lysosome.

Free Ribosomes: They make proteins that stay within the cytoplasm. The cell uses these proteins itself.

You will now create a poster of the endomembrane

system to demonstrate your understanding of how all the

organelles work together.