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Ch 5 – Protein Synthesis. Differences between DNA & RNA. Contains the sugar deoxyribose Contains thymine Is in the shape of a double helix There is only 1 type of DNA DNA can’t leave the nucleus DNA is much longer Only organic molecule that can replicate itself .
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Differences between DNA & RNA • Contains the sugar deoxyribose • Contains thymine • Is in the shape of a double helix • There is only 1 type of DNA • DNA can’t leave the nucleus • DNA is much longer • Only organic molecule that can replicate itself • Contains the sugar ribose • Contains uracil instead of thymine • Is a single strand • There are 3 types of RNA (m-RNA, r-RNA, t-RNA) • RNA leaves the nucleus • RNA is shorter • Needs a DNA template to be made DNA RNA
3 types of RNA (ribonucleic acid) • m-RNA – messenger RNA – forms by transcription and copies the “message” of the DNA to take out to the ribosomes to instruct the formation of specific proteins • t-RNA – transfer RNA – responsible for transfering specific amino acids to the ribosome as an amino acid chain is assembled into a protein • r-RNA – Ribosomal RNA – a structural component of a ribosome- along with proteins it forms the ribosomes
Protein Synthesis at a glance This is what we did in the DNA lab!
The Delivery Route • Messenger RNA (mRNA) is the blueprint for construction of a protein. • Ribosomal RNA (rRNA) is the construction site where the protein is made. • Transfer RNA (tRNA) is the truck delivering the proper amino acid to the site at the right time. tRNA
One Gene- One Enzyme Theory How Protein Synthesis came to be recognized as the Central Dogma of Molecular Genetics
Garrod’s Hypothesis • Archibald Garrod – (early 20th century) – studied the disease alkaptonuria and hypothesized that a defective enzyme caused an “inborn error of metabolism” along a reaction pathway - see pg. 234
One Gene- One Enzyme Hypothesis • Alkaptonuria – Black urine disease • Ear wax will turn red or black when exposed to air • Sweat is brown in color • Caused by a defective enzyme so the amino acid tyrosine doesn’t degrade properly and a toxic byproduct called homogentisic acid builds up
If there is an accumulation of Substance B then enzyme 2 must be defective.
Beadle and Tatum • 33 years later, they worked with bread mold Neurospora crassa & exposed spores to x-rays to create mutant strains. Through their experiments they concluded: a gene acts by directing the production of only one enzyme - called the one gene-one enzyme hypothesis.
Vernon Ingram • by using Beadle and Tatum’s work, he showed that sickle cell anemia results from alteration of a single gene . Many hereditary diseases have been traced to this type of alteration in just one gene.
Starting Protein Synthesis • DNA controls all the cell activities – largely by controlling the production of thousands of proteins – many of which are specific to each cell. • Protein synthesis begins when the DNA “unzips” – nucleotides of mRNA (messenger RNA) find their complementary base and join into a chain. A pairs with U and G pairs with C
TRANSCRIPTION • Once the chain is fused, the mRNA moves away from the parent DNA strand which then rejoins. • This completes the process of transcription (the message of the DNA has been TRANSCRIBED into the mRNA. • The mRNA now leaves the nucleus and goes out to a ribosome.
The Language of Genetics • Nucleotides are arranged in a linear sequence, some are several thousands long. • A single base does not contain a code. • Westandonguardforthee
Reading the DNA code • Rather three bases or TRIPLETS carry the code. Like a book that contains only three nucleotides (triplets). • From the 4 bases (A, U, C, G) there are 64 possibilities for triplet formation. • These three letter codes determine the exact order in which amino acids will be arranged in a specific protein molecule. Books containing Triplets!
UNZIPPING DNA • RNA polymerase (an enzyme) opens the part of the DNA to be transcribed. • Only one strand of DNA (called the template strand) is transcribed. • RNA nucleotides are available in the region of the chromatin and are linked together similar to the DNA process.
Codons • After RNA is transcribed it detaches itself and may be stored for a short time in the nucleolus or move immediately through the nuclear pores into the cytoplasm. • The RNA has the code for specific amino acids. • This type of RNA is called mRNA. • Like DNA there are 64 combinations of codons in mRNA.
Translation • mRNA acts as the template for the assembly of amino acids and the production of protein molecules. • Ribosomes help read(translate) the mRNA to. determine which amino acids are selected.
Amino Acid trains • Throughout the cytoplasm we find amino acids. • The sequence which they join together during synthesis is determined by the mRNA codons. • The amino acids are picked up and brought to the template using tRNA.
Anticodon • The tRNA carries the amino acids to the mRNA using coding that is the exact opposite of the code found on the mRNA known as an anticodon. • The anticodon tells the specific amino acid to come to the mRNA. • After the tRNA delivers the amino acid it moves to the cytoplasm.
Upon completion of the chain, the protein is released and passes into the cytoplasm where it is used.