Protein Synthesis
description
Transcript of Protein Synthesis
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Protein SynthesisChapter 8
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A. What is protein synthesis?1. Also called gene expression2. Central dogma of molecular biology: information flows from DNA RNA proteins
(Defined by Francis Crick)3. So…a section of DNA (gene) is
designed to create a specific protein
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B. RNA
1. What is RNA?a. Ribonucleic Acidb. Acts as a messenger between DNA and ribosomesc. Gives ribosomes instructions for making proteins
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2. Structure of RNAa. Like DNA, made up of a
long chain of nucleotidesb. Unlike DNA, RNA is single
strandedc. Nucleotide is different
i. Phosphate is the same
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ii. Sugar – ribose (instead of deoxyribose in DNA)iii. Bases – adenine, cytosine, guanine and uracil (instead of thymine)
- Cytosine-Guanine (C-G)- Adenine-Uracil (A-U)
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Structure of RNA
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C. Transcription – transfer of info from DNA to RNA (Look at page 227!)1. Begins on one end of the gene – promoter/start signal
2. DNA molecule unzips3. Free RNA nucleotides match up by
base pairing4. RNA molecule detaches and DNA molecule re-zips
5. Stops at end of gene – stop signal6. Enzyme – RNA Polymerase
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7. The RNA molecule formed is called messenger RNA (mRNA)a. Complementary to DNA; made in
the nucleusb. Leaves the nucleus & goes to
ribosome (in the cytoplasm)c. Contains the information needed
for protein synthesis
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Transcription
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D. How is the genetic code used to make proteins?
1. Proteins are made by putting a string of amino acids (aa) together2. There are 20 different amino acids
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3. Different proteins are created by putting amino acids
together in different sequences4. RNA instructions are written in groups of three nucleotides
called a codon5. Each codon matches up with a specific amino acid (Look at
page 230!)
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a. There may be more than one codon for an amino acid
b. Promoter/Start codon: AUG(methionine)
c. Stop codon: UAA, UAG and UGA
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E. Translation – using mRNA instructions to make proteins (Look at page 232!)
1. mRNA attaches to a ribosome
2. Transfer RNA (tRNA) brings amino acids over to the
ribosome and matches up with the mRNA
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3. Anticodons on tRNA molecules match up (base pairing) with the codons on the mRNA molecules
4. As the tRNA matches up with the mRNA (anti-codon to codon), a bond forms between the amino acids
5. Once the bond between amino acids forms, the tRNA releases the aa and leaves to find another aa
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Translation
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F. Regulation of Gene Expression1. All cells within an organism have
the exact same genes, but different types of cells express different combinations of genes2. Genes can also be turned on & off
a. Operator – turns a gene onb. Repressor – turns a gene off
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G. Gene Structure1. Not all DNA contains information needed to make proteins2. Introns – sections of a gene without coding information (not used to make proteins)3. Exons – sections of a gene that do have information to make proteins
“exons are expressed”4. Before translation, the introns of mRNA are cut out, and the exons are spliced back together
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H. Mutations – changes in DNA1. Move gene to a new location?
a. Gene rearrangementb. New regulatory control
gene might be turned on when it should be turned
off (or vice versa)
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2. Change a gene? Gene alterationa. The amino acid sequence is affectedb. Point Mutation – single nucleotide changes (ATG AAG)
(one amino acid affected)c. Frameshift Mutation – affects the
whole gene (whole protein affected)
i. Insertion (ATG ATAG)ii. Deletion (ATG AG)
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iii. Example of a frameshift mutation (caused by a deletion)
The dog ate the cat.(Delete the d in “dog.”)
The oga tet hec at.
After the deletion, the sentence (protein) doesn’t make sense!
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DNA GAT
mRNA codon
UAU
tRNA anticodon
UUC
Amino acid
tryptophan