1. From DNA to Protein
Ch 9

2. RNA Ribonucleic Acid Nucleic acid, single strand
Contains the sugar ribose
RNA has the same base pairing rule as DNA, but it has Uracil instead of Thymine
A – U
C – G
Three major types of RNA
mRNA, rRNA, tRNA

3. Ribonucleic Acid
Messenger RNA (mRNA): forms complementary to one strand of DNA, contains amino acid sequence (protein- building message) and carries it from the nucleus to the ribosome to direct the synthesis of a specific protein
Ribosomal RNA (rRNA): main component of ribosomes, assembles amino acids into polypeptide chains
Transfer RNA (tRNA): delivers amino acids to a ribosome during protein synthesis

4. Gene Expression
Transcription and translation are part of gene expression:
Multistep process by which information from genes guides the assembly of an RNA or protein product
DNA is TRANSCRIBED into RNA, RNA is TRANSLATED into proteins

5. Transcription Transcription: synthesis of DNA code into mRNA
The DNA is unzipped in the nucleus
An enzyme called RNA polymerase moves along the template DNA strand
It reads the template strand and a complementary mRNA strand is synthesized [uracil is substituted for thymine]
When the polymerase reaches the end of the gene, the mRNA is released and moves into the cytoplasm through nuclear pores

7. Transcription mRNA code is significantly shorter than DNA
Introns: interrupting sequences that DO NOT code for anything, these are removed before the mRNA leaves the nucleus
Exons: The coding regions where the genes are located, stay in the mRNA
In a process called alternative splicing, exons are rearranged and spliced together in different combinations producing multiple versions of a gene

8. Transcription
Codon: sequence of three nucleotide bases that code for an amino acid (or stop signal)
Amino acids make up proteins, proteins are building blocks of cells and enzymes
The sequence of bases in a triplet determines which amino acid the codon specifies
Codons occur one after another in an mRNA, and when it is translated, the order of codons determines the order of amino acids in the resulting polypeptide
Some signal the beginning or end of a protein-coding sequence

10. Translation
Translation: sequence of codons in mRNA is read and translated to make a protein
Anticodon: a triplet of tRNA nucleotides that base-pairs with an mRNA codon
Once in the cytoplasm, mRNA moves to a ribosome
The tRNA anticodon binds to the mRNA codon in the ribosome
Additional tRNA’s continue to move into the ribosome, binding to additional mRNA codons as the mRNA moves through the ribosome like a ribbon.

12. Translation
The ribosome forms peptide bonds between the amino acids, growing polypeptide (protein) chain
As the ribosome moves the next codon, it releases the tRNA
This continues until a stop codon is reached and then protein synthesis stops
The amino acid chain (polypeptide) folds into a protein

14. Mutations
When a mutation occurs in a protein-coding region, the redundancy of the genetic code offers a margin of safety
a mutation that changes a CCC codon to CCG may not have further effects, both of these specify the amino acid serine
Other mutations may change an amino acid in a protein or result in a premature stop codon that shortens it
Mutations that alter a protein can have drastic effects on an organism

15. Mutations
Base-Pair Substitution: chemical change in just 1 base pair 
Insertion: addition of a nucleotide to the DNA sequence
Deletion: removal of a nucleotide to the DNA sequence
Insertions and deletions result in frameshifts
Mutations can lead to genetic disorders or can be harmless

17. Mutations
Sickle cell anemia occurs because of a base-pair substitution
Causes hemoglobin molecules to clump together and red blood cells to form a crescent (sickle) shape
Sickled cells clog tiny blood vessels, disrupting blood circulation throughout the body

18. Ricin Ricin is a ribosome-inactivating protein (RIP)
RIPs remove adenine bases from rRNAs which halts protein synthesis
Death from ricin exposure occurs in days due to low blood pressure and respiratory failure
A dose of ricin as small as a few grains of salt can kill an adult human

19. Ricin
Bulgarian spy’s weapon: an umbrella modified to fire a tiny pellet of ricin into a victim. An umbrella like this one was used to assassinate Georgi Markov on the streets of London in 1978.