protein synthesis

Protein SynthesisChapter 8

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

B. RNA

1. What is RNA?a. Ribonucleic Acidb. Acts as a messenger between DNA and ribosomesc. Gives ribosomes instructions for making proteins

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

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)

Structure of RNA

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

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

Transcription

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

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!)

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

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

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

Translation

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

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

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)

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)

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!

DNA GAT

mRNA codon

UAU

tRNA anticodon

UUC

Amino acid

tryptophan