Protein Synthesis

5.1 I can explain the steps in the process of transcription, along with where they take place (this includes the role of DNA and mRNA) 5.2 I can explain the steps in the process of translation, along with where they take place (this includes the role of mRNA, tRNA, ribosomes (rRNA), and amino acids) 5.3 I can list the three different types of RNA and describe the function of each. 5.4 I can describe at least three differences between DNA and RNA. 5.5 I can label the following items in pictures of transcription and translation: DNA sense strand, DNA nonsense strand, RNA polymerase, mRNA strand, ribosome, start codon, stop codon, amino acid, polypeptide chain (protein), tRNA, anti-codon, peptide bond 5.6 I can describe at least three different types of mutations in DNA, and their possible effects on the organism.

I can explain the steps in the process of transcription, along with where they take place (this includes the role of DNA and mRNA)

Every cell faces a fundamental problem when making proteins.  The instructions for making the proteins are in the nucleus on the DNA. BUT…  The location for making proteins is outside the nucleus at the ribosomes.

 The first part of the solution is a process called… …TRANSCRIPTION

 First, an enzyme called RNA polymerase attaches to DNA at the beginning of a gene.  The enzyme “unzips” the double helix strand and begins to “read” the instructions, coded in the sequence of the letters A, T, C, and G.

 As the enzyme reads the DNA code, it copies it by attaching complementary RNA nucleotides.  The result is a strand of mRNA (messenger RNA) which carries the instructions for making a protein. RNA polymerase RNA nucleotide Growing mRNA strand

 Well, we’re making a copy of the DNA, and the DNA can be found where? In the nucleus.  The DNA can’t leave the nucleus for two reasons: It’s too large to get through the pores, and it’s too precious to send it out into the cytoplasm where digestive enzymes could break off pieces of it.

 …it leaves the nucleus to go take the DNA’s message to a ribosome where the protein will be made.  So mRNA solves the problem of getting the information from the nucleus to the cytoplasm.  Now to make the protein!!

I can explain the steps in the process of translation, along with where they take place (this includes the role of mRNA, tRNA, ribosomes (rRNA), and amino acids)

 The cell has another problem. It has to take the “language” of nucleic acids (DNA/RNA) and turn it into the language of amino acids (protein).  So it needs a translator… …otherwise known as the ribosome!

 First, the mRNA threads into the ribosome, until the “start codon” – AUG, reaches the P site in the ribosome.

 Next, the ribosome brings in a tRNA (transfer RNA).  On one end of the tRNA is an anti-codon that is complementary to the codon on the mRNA.  On the other end of the tRNA is an amino acid.

 A tRNA also binds at the A site. A peptide bond forms between the two amino acids, connecting them together.  Then the tRNA in the P site leaves (leaving behind its amino acid), and the ribosome moves to the next codon. The process continues this way until it reaches a stop codon.

 Once the ribosome reaches a stop codon, everything detaches.  The protein finishes its production by folding a certain way so that it can do its job.  The ribosome will make another protein.  The mRNA gets recycled by digestive enzymes in the cytoplasm.  The tRNA will pick up more of their amino acids to help build another protein.

I can list the three different types of RNA and describe the function of each.

1. mRNA (messenger RNA) – carries the message of the DNA from the nucleus to the ribosome; created during transcription. 2. tRNA (transfer RNA) – transfers amino acids to the growing chain of amino acids in the ribosome during translation. 3. rRNA (ribosomal RNA) – what ribosomes are made of.

I can describe at least three differences between DNA and RNA.

DNA: Double-stranded Deoxyribose is the sugar G, C, A, and T are the bases Very long RNA: Single-stranded Ribose is the sugar G, C, A, and U are the bases Much smaller (one gene)

I can label the following items in pictures of transcription and translation: DNA sense strand, DNA nonsense strand, RNA polymerase, mRNA strand, ribosome, start codon, stop codon, amino acid, polypeptide chain (protein), tRNA, anti-codon, peptide bond

DNA nonsense strand mRNA strand DNA sense strand RNA polymerase

tRNA Peptide bond Polypeptide chain Amino acid Stop codon mRNA strand Start codon anticodon ribosome

I can describe at least three different types of mutations in DNA, and their possible effects on the organism.

 There are two main categories of mutations that we discuss:  Chromosomal mutations, which involve changes in whole genes on a chromosome (we will look at these next unit)  Gene mutations, which involve changes in parts of genes.

 There are two main types of gene mutations: point mutations, and frameshift mutations.  A point mutation is when one base is switched out for another base. It only affects that one amino acid in the sequence.  A frameshift mutation is when one base is deleted or added, which shifts all the bases after it, affecting all of the amino acids in the sequence after the mutation.

 Let’s say the following sentence is a gene, and each word in the sentence is a codon (even though the words have more than three letters): Biology students are really nice people.

 For a point mutation, one base is switched for another base. Biology students ate really nice people.  We changed the “r” in are to a “t.”  As you can see, only one word was affected.  However, the whole meaning of the sentence has changed.

 Look at your codon chart. Is every amino acid coded for by one codon?  No! There are repeats, right?  So if we changed the last base of the codon, sometimes it would still code for the same amino acid.  If this is the case, is there any change in the protein?  No – we call it a silent mutation because there was no effect on the organism.

 In an addition mutation, one base is repeated. So we will add one letter twice. Biology students sar enic epeopl e.  We put in an additional “s” after students.  Now, every word (or codon) after the addition is affected because every base afterward is shifted down one.

 In a deletion mutation, one base is deleted from the sequence. Biology studenta ren icep eople.  We deleted the “s” at the end of students.  Now, it shifts all the bases afterward up one.

 Effects of mutations can be minor, or severe. They can be beneficial, harmful, or as we’ve seen, neutral.  It’s hard to discuss which type is “worse” than others, because while frameshifts render the entire protein useless and may appear worse at a glance, point mutations can be equally devastating.  Let’s take a look at one such case.