click here to read the case study about protein synthesis.here
TRANSCRIPT
RNA and Protein Synthesis
Mrs. McNamaraChapter 10-2 and 10-3 (pgs 190-197)
• Click here to read the case study about protein synthesis.
Making ProteinsBig Question:
How do cells use the genetic information stored in DNA to make millions of different proteins the body needs?
Key Concept:
• Genetics shows that genes code for proteins.
Making ProteinsRemember: each gene consists of a linear sequence of nucleotides arranged in a specific order according to our genetic ancestry.
The order of these nucleotides makes up the genetic information or “code” which determines the sequence of amino acids that will be assembled.
C T G A ...
sugar-
phosphate-
sugar-
phosphate-
sugar-
phosphate-
sugar-
phosphate-
...
Making Proteins Proteins are made up of a linear sequence of amino acids that get twisted up.
And, in all cells, except for bacteria, DNA is stored in the nucleus and protein synthesis takes place in the ribosome (located in the cytoplasm)…
Ribosome
• If a gene is used to make a protein, we say that gene is “expressed”.
Be able to answer the following questions. You will have to answer a question at the start of class tomorrow:
• What is a gene?• What is a protein made of?• What do we mean when we say a
gene is expressed?
Key Concept:
• The genetic code carried by RNA is translated into amino acid sequences of proteins.
Problem:• DNA cannot leave the nucleus (it is
TOO BIG!)
How can we get DNA’s information from the nucleus to the ribosomes (site of protein synthesis)?
We use RNA to move DNA’s code from the nucleus to the ribosome!
3 Types of RNA:• 1. mRNA• 2. tRNA• 3. rRNA
• RNA: ribonucleic acid. Takes DNA information to the ribosome and uses information from DNA to make proteins.
Comparison of DNA and RNA:Nucleotide Components Function Form/Structure
Sugar Nitrogen Base
DNA Deoxyribose
Adenine, Guanine, Cytosine,Thymine
Store and transmit genetic info. that tells cells which proteins to make and when.
2 strands of nucleotides.
Double Helix
RNA Ribose Adenine, Guanine, Cytosine, Uracil
Move genetic info. from DNA to ribosomes; assemble polypeptide chains.
Single strand of nucleotides.
Single Helix
FYI - RNA Hey kids…RNA differs from DNA in several ways.
•An RNA molecule has only one side of the ladder shape. •RNA has the bases A, G, and C. However, it has a base U or Uracil, instead of base T or thyamine.•So when forming base pairs, base A pairs with base U.
1. mRNA (Messenger RNA)• Structure-single, uncoiled strand of RNA
nucleotides.
• Function-takes information from DNA (in nucleus) to ribosome to use during protein synthesis. Used as a template for the assembly of amino acids during protein synthesis.
• mRNA is made from DNA in the nucleus.
• mRNA is “read” in order in 3 base “groups”.• Each called a CODON- a 3-base sequence of
mRNA that codes for a specific amino acid.• 3 mRNA bases=1 codon= code for 1 amino acid• 64 different codons exist…several will code for
the SAME amino acid.
Two Important Types of Codons:
• START CODON-tells the ribosome to begin reading the mRNA and to bring and assemble a chain of amino acids (begin translation). • This codon and amino acid is the same in
EVERY PROTEIN.• STOP CODON-tells the ribosome to stop reading
the mRNA. No more amino acids are brought and assembled (stop translation-ends the assembly of the protein).
Stop and Think:
3 mRNA bases = code for 1 amino acid
If you have 450 mRNA bases, how many amino acids would you code for?
How many codons would you have?
2. tRNA (Transfer RNA)
• Structure-single strand of RNA nucleotides folded into a hairpin shape.
• Function-pairs with mRNA to transfer amino acids into the growing polypeptide chain in the correct sequence.
• How does the tRNA know where to bring the amino acids (what order)?• One end of the tRNA is an ANTICODON-3-base
sequence of tRNA that complements (fits into) an mRNA codon.
• The tRNA brings the amino acid to the codon that it fits into.
Be able to answer the following questions. You will have to answer a question at the start of class tomorrow:• How is RNA able to move DNA’s information out of
the nucleus?• If a strand of mRNA has 1500 bases, how many
codons is that? How many amino acids does it call for?
Key Concept(s):
• DNA Expression begins with its transcription to RNA.
• Translation of the genetic code is mediated by tRNA and ribosomes.
Making Proteins
Protein Synthesis takes place in two steps:
1. Transcription2. Translation
Like copying a cookie recipe from a cookbook, then baking the cookies.
• 1. TRANSCRIPTION-mRNA is made from DNA in the nucleus.
Making Proteins
How does mRNA get made?1. RNA polymerase (enzyme) unzips section of
DNA.• This section is a GENE-piece of DNA that
codes for a protein.
2. RNA polymerase moves along one side of the DNA causing complementary mRNA nucleotides floating in the nucleus to be assembled.
3. RNA polymerase reaches the termination sequence of the gene and releases mRNA and DNA.
4. DNA zips back up; mRNA leaves the nucleus.
How does the mRNA only assemble for one section of DNA (one gene)?
• PROMOTER-beginning of the gene being transcribed. Tells transcription to begin.
• TERMINATION SEQUENCE-end of the gene being transcribed. Tells the RNA polymerase “let go”.
Now, how does the template of bases found in the mRNA get used to assemble the protein?
This requires “translating” the nucleotide-base language of mRNA to the new, amino acid language of protein synthesis.
Making Proteins
TRANSLATION:the second step of protein synthesis; (enzyme assisted!!) the ribosomes ‘read’ the mRNA base sequence in groups of three bases (called a codon). Amino acids are transferred to growing chain by tRNA.
Making Proteins - Translation
Remember: the tRNA anticodon (sequence of 3 bases) fits into an mRNA codon; when they fit together, that is the spot in the chain the amino acid will occupy.
Making Proteins - Translation
How does the amino acid chain get assembled?1. mRNA goes to ribosome (proteins made here).
2. Ribosome reads mRNA from start codon to stop codon.
3. As the ribosome reads each codon, the corresponding tRNA will come and match its anticodon to the correct codon.
4. The amino acid carried by the tRNA will be linked to the prior amino acid in the chain.
5. Ribosome repeats 2-4 until itreads the stop codon and the process stops.
mRNA codon and corresponding amino acids.
The diagram below shows a ribosome attach to mRNA, and then move along the mRNA adding amino acids to the growing polypeptide chain.
Making Proteins
Part 2: Translation
Let’s Review:
DNA makes RNA makes PROTEIN.
It is a 2 - step processTranscription - when DNA makes a copy of the protein recipe. The copy is called mRNA. Translation - when the ribosome makes the protein. Has helper molecules called tRNA that carry the amino acids.
Except for bones, fat, and water, the rest of your body is made of protein.
Examples of protein functions
Function Description ExampleAntibody Antibodies bind to specific foreign
particles, such as viruses and bacteria, to help protect the body.
Immunoglobulin G (IgG)
Enzyme Enzymes carry out almost all of the thousands of chemical reactions that take place in cells. They also assist with the formation of new molecules by reading the genetic information stored in DNA.
Phenylalanine hydroxylase
Messenger Messenger proteins, such as some types of hormones, transmit signals to coordinate biological processes between different cells, tissues, and organs.
Growth hormone
Structural component
These proteins provide structure and support for cells. On a larger scale, they also allow the body to move.
Actin
Transport/storage These proteins bind and carry atoms and small molecules within cells and throughout the body.
Ferritin
Making Proteins
Summary:
• Let’s watch protein synthesis in ACTION!
Be able to answer the following questions. You will have to answer a question at the start of class tomorrow:
• Why is protein synthesis important to your life?
• What are the two parts of protein synthesis – summarize them VERY BRIEFLY.
• What is tRNA’s role in protein synthesis?