From Gene to Protein Chapter 17

One Gene One Enzyme

Genes The DNA provides the instructions to make the protein RNA is the link between gene and protein DNA codes for RNA and RNA codes for the protein

Transcription/Translation The DNA and RNA molecules that are composed of nucleotide monomers When converting from DNA to RNA you are simply transcribing the code from the language of DNA nucleotides to RNA nucleotides Proteins are “written” in the language of amino acids When converting from RNA to protein we are translating from the nucleotide language to amino acid language

RNA In what ways are RNA molecules different from DNA? RNA is single stranded In RNA, Uracil replaces Thymine Nucleotides have ribose instead of deoxyribose In eukaryotes, RNA leaves the nucleus

What are the functions of the 4 different types of RNA?

The Genetic Code RNA consists of four “letters” A, U, G, and C Proteins consist of 20 “letters” the amino acids If 1 RNA base codes for 1 amino acid, then only 4 amino acids can be coded for

How many different amino acids can be coded for if 2 RNA’s code for 1 amino acid? 4 2 = 16 : Not enough! How many different amino acids can be coded for if 3 RNA’s code for 1 amino acid? 4 3 = 64: More than enough for the 20 different amino acids….

There is redundancy in the code but not ambiguity!

The Code is Universal The code is shared by almost all organisms CCG codes for what amino acid? Proline. This holds true for all species of living organisms Bacteria, therefore can be programmed to synthesize human proteins by inserting human DNA

In prokaryotes, RNA is directly translated into the polypeptide

RNA in eukaryotes is processed before translation

The function of the cap is: ◦ prevent mRNA degradation by hydrolytic enzymes ◦ helps attach to the ribosome Function of the 3’ tail: ◦ same functions as the 5’cap ◦ also helps facilitate export of mRNA from nucleus

RNA splicing Removes noncoding regions called introns snRNP (short nuclear ribonucleoproteins) recognize the splicing signals that are at the ends of introns The RNA in the snRNP is called snRNA (small nuclear RNA) spliceosome is the larger protein assembly that surrounds the snRNP The spliceosome cuts and releases the introns, and then joins exons together The spliceosome cuts and releases the introns, and then joins exons together

Evolutionary role of introns Introns may play regulatory role Different intron removal may lead to different proteins Introns may enhance crossing over between homologous regions by increasing the distance between exons

Peptide Bonds Join Amino Acids

Messenger RNA consists of leader, reading frame, and trailer sequences.

Ribosomes, consist of two subunits, each of which contains rRNA and ribosomal proteins.

tRNAs bring amino acids to the ribosomes during translation to be assembled into polypeptide chains.

tRNA Assembly

Initiation of Translation Initiation of Translation

Elongation

Termination

review

Polyribosomes

Mutations