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Protein Synthesis. Chapter 12. What is a protein?. Proteins are macromolecules made up of amino acids . Some proteins, like those in your hair, are structural and provide shape. Other proteins called enzymes speed up chemical reactions. Proteins are made by ribosomes. What is RNA?.
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Protein Synthesis Chapter 12
What is a protein? • Proteinsare macromolecules made up of amino acids. Some proteins, like those in your hair, are structural and provide shape. • Other proteins called enzymes speed up chemical reactions. • Proteins are made by ribosomes.
What is RNA? • Ribonucleic acid (RNA) is a macromolecule with a structure similar to DNA. RNA is also made up of nucleotides, but it has a different nucleotide and serves a different function. • There are also three forms of RNA • 1. messenger RNA (mRNA)= used in transcription • 2. transfer RNA (tRNA) = used in translation • 3. ribosomal RNA (rRNA) = makes up ribosomes
DNA vs. RNA DNA • Double helix • Has the bases A, T, G, C • One type • Genetic material RNA • Single helix • Has the bases A, G, C, and U (uracil) • Three types (mRNA, tRNA, rRNA) • Primarily used for protein synthesis
How is a protein made? • Protein Synthesis is the process of making a protein. There are two main steps: • Transcription • Translation
Transcription • DNA is the genetic code found in the nucleus and contains the instructions for life functions, including how to make a protein. • When a cell needs a particular protein, an enzyme called RNA Polymerase bonds to a piece of DNA at the promoter site. The promoter signals the beginning of a DNA sequence that has the instructions for a protein.
Transcription (cont) • As RNA polymerase reads the DNA, it makes a piece of mRNA in the nucleus. This mRNA carries the instructions in RNA language. • The mRNA is the COMPLEMENT of the DNA strand in RNA language. This means that T’s are replaced with U’s (uracil)
Transcription (cont) • As RNA polymerase pieces together mRNA, it does so by reading codons. • Codonsare like three letter words in RNA language. For example, a codon in RNA might be AAU, GCA, etc.
Transcription (cont) • For example, if the DNA strand reads: • G A T T A C • Then the mRNA strand will read: • CUA A U G
Transcription (cont) • What is the mRNA strand for the following strands of DNA? 1. C A T G C C 2. A T T G C A
Transcription (cont) • Answers: 1. G U A C G G 2. U A A C G U
Transcription (cont) • After RNA polymerase has completed making the strand of mRNA, it “edits” the message through a process calledsplicing. • Some parts of the mRNA are removed from the mRNA message. The pieces that are removed are called introns. The remaining pieces are called exons because they are EXpressed in the edited mRNA.
Transcription (cont) • Why is mRNA edited? • Possible reasons: • DNA sequence might make more than one protein? • Evolution?
Translation • Once transcription is complete, the mRNA molecule moves out of the nucleus and into the cytoplasm. It then attaches to a ribosome for the next step, translation.
Translation (cont) • The ribosome “reads” the mRNA codons with the assistance of tRNA. On one side of tRNA is an anti-codon, the complement of the mRNA molecule. On the other side of tRNA is an amino acid corresponding to the anti-codon.
Translation (cont) • Although there are 64 combinations of nucleotides, there are only about 20 amino acids because some repeat.
Translation (cont) • You can find the name of the amino acid by using the chart on the next slide. • The first letter in the anticodon is found in the center circle, the second letter in the middle circle, and the third letter in the outermost circle.
Translation (cont) • For example, you can find the name of the amino acid for AUG by using the chart this way. • The first letter is in the center circle.
Translation (cont) • The second letter is in the middle circle
Translation (cont) • The third letter is the outermost circle, and the name of the amino acid is written next to it, just outside of the circle. • AUG is methionine.
Translation (cont) • What is the name of… • GUC? • UGA?
Translation (cont) Answers • GUC = Valine • UGA = Stop
Translation (cont) • The tRNA anticodons line up next to the mRNA as the ribosome processes and connects the amino acids forming a polypeptide.
Protein Synthesis Review • DNA is the genetic material in the nucleus. • RNA polymerase transcribes the instructions in the DNA into mRNA. • mRNA is edited through splicing. Introns are removed; exons are expressed.
Protein Synthesis Review (cont) • mRNA ‘s codons are read by the ribosome during translation. • tRNA molecules that carry amino acids match their complementary anti-codons alongside the mRNA. • The ribosome processes and connects the amino acids to form polypeptides which shape into proteins.
Levels of Organization for a Protein • Primary structure – order of amino acids • Secondary structure – how the individual peptides fold • Alpha helixes • Beta sheets
Levels of Organization for a Protein (cont) • Tertiary structure – how the helixes and sheets fold onto themselves to form subunits • Quaternary structure – the completed protein with all subunits in place
Enzymes • Recall that enzymes are special proteins that catalyze (speed up) chemical reactions. • Enzymes are necessary to carry out the functions of life. • Enzymes can become damaged if exposed to extreme conditions such as heat. This is called denaturing the enzyme.
How do enzymes work? • Enzymes are highly specialized and only bond to certain materials called substrates. However, they are able to bend to better fit the substrate at their bonding site. • After the chemical reaction is complete, the enzyme removes itself from the substrate and moves on to another substrate.
