Human Anatomy & Physiology
02.5 Protein Synthesis
Cells make products in order to repair worn out or damaged parts,
hormones, enzymes, fibers, etc. and use them within the cell or
release them outside to be used elsewhere.
The instructions for the proteins that will replace these parts or
become cell products is a section of DNA known as a gene.
A gene is a designated section of the DNA ladder that codes for a
specific protein
 Slight Problem…if the DNA is in the nucleus and it cannot
leave and the ribosomes, which make the proteins, are outside
the nucleus, then how can the instructions to make the protein
be given to the ribosome?
RNA!!!!!
 Ribonucleic Acid
 Built a lot like DNA with the exception of a few differences:
1. Ribose is the sugar not Deoxyribose
2. RNA is only half a ladder (so it only copies one strand of the
gene)
3. RNA has no thymine.
It uses Uracil instead. (Remember, NO T’s in RNA!)
4. RNA can move in and out of the nucleus, where DNA has to
stay in the nucleus.
There are Three types of RNA:
Messenger RNA = responsible for copying the gene and taking it to
the ribosome.
Ribosomal RNA = ribosomes
Transfer RNA = responsible for getting the amino acids and placing
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them in the correct order on the mRNA strand (also known as a
template)
RNA and DNA both use the nucleotide as their monomer.
OK…now we know about RNA, let’s make a protein!
Protein Synthesis has two major steps:
1. Transcription
 Messenger RNA will make a copy of the segment of the DNA
strand known as a gene.
 Genes Code for one specific protein. These proteins can be
enzymes, hair, nails, etc.
 Proteins often cause one to look a certain way and the
characteristics are known as traits.
2. Translation:
 Once the DNA gene has been copied into messenger RNA
(mRNA), then the mRNA will need to be ‘read’ to build a
protein.
Working the Steps of Protein Synthesis:
1. RNA helicase (sound familiar!) opens the gene to be copied.
2. Messenger (mRNA) nucleotides come in match up to ONLY one
side of the DNA ladder.
3. Once mRNA has finished, it has made a copy of the gene blueprint
or instructions, which is now called a template.
Save space for a DIAGRAM here
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.
Transcription is complete!
DNA gene has been copied into a mRNA template.
4. The mRNA template must now leave the nucleus through one of
the nuclear pores and go to the protein factories…Ribosomes!
Save space ~ 5-7 lines for DIAGRAMS here.
 One ribosomal unit (ribosomal RNA) will attach to the bottom
of the template and another directly over the top.
 It takes TWO ribosome units to ‘read’ the template.
5. Notice how the ribosomes are only reading 3 bases at a time.
 Three bases code for ONE amino acid.
This three base unit is called a CODON.
6. There are 20 different amino acids that can be used to make a
protein chain. In order to make things a little simpler, we will just
use numbers of represent the 20 different amino acids (aa) instead of
their name abbreviations.
Transfer RNA (tRNA) will go and get the exact amino acid needed
from the cytoplasm and bring it to the matching codon.
Remember that chicken or hamburger, or salad that you ate? The
protein in this food was broken down into independent amino acids.
Your circulatory system delivered the amino acids to your cells!
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Notice that the tRNA has an end that matches the codon! This end is
known as the anticodon. This assures that the tRNA will place the
amino acid in the exact spot needed in the protein.
Wrong spot or the wrong amino acid in that spot = different protein
will be the result of that mistake!
7. Step 7 continues as the ribosomes pull the mRNA template
through. As amino acids are placed next to one another, they form a
peptide bond. Once they have formed the bond, the tRNA is released
to go and get another amino acid if called for.
8. The amino acid chain is complete once the ending or stop codon is
read. The primary protein chain will now (under most circumstances)
be placed into the Rough ER for transportation.
9. The new protein will fold or be combined with other stands to
form secondary and then tertiary structures. The rough ER will
transport the protein and then send it, via a synaptic vesicle (Think of
synaptic vesicles as cell taxis!), to the Golgi apparatus or body.
Here the Golgi will package the protein for its final transportation.
Leave ⅓– ½ a page for practice making a protein from the given DNA strand.
Remember to:
Reduce, Recite, Reflect, & Review!
Make your Flashcards & Study 3 x 5!
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