From Gene to ProteinFrom Gene to ProteinChapter 17

One Gene One EnzymeOne Gene One Enzyme

GenesGenesThe DNA provides the

instructions to make the protein RNA is the link between gene and

proteinDNA codes for RNA and RNA

codes for the protein

Transcription/TranslationTranscription/TranslationThe DNA and RNA molecules that are

composed of nucleotide monomersWhen 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

RNARNAIn what ways are RNA molecules

different from DNA?RNA is single strandedIn RNA, Uracil replaces ThymineNucleotides have ribose instead

of deoxyriboseIn eukaryotes, RNA leaves the

nucleus

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

The Genetic CodeThe Genetic CodeRNA consists of four “letters” A,

U, G, and CProteins consist of 20 “letters”

the amino acidsIf 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?

42 = 16 : Not enough!How many different amino acids

can be coded for if 3 RNA’s code for 1 amino acid?

43 = 64: More than enough for the 20 different amino acids….

There is redundancy in the code but not ambiguity!

The Code is UniversalThe Code is UniversalThe code is shared by almost all

organismsCCG codes for what amino acid?Proline. This holds true for all

species of living organismsBacteria, 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 splicingRNA splicingRemoves noncoding regions called

intronssnRNP (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

Evolutionary role of Evolutionary role of intronsintronsIntrons may play regulatory roleDifferent intron removal may

lead to different proteinsIntrons may enhance crossing

over between homologous regions by increasing the distance between exons

Peptide Bonds Join Amino Peptide Bonds Join Amino AcidsAcids

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

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

tRNAs bring amino acids to the tRNAs bring amino acids to the ribosomes during translation to be ribosomes during translation to be

assembled into polypeptide chainsassembled into polypeptide chains. .

tRNA Assembly

Initiation Initiation of of TranslatioTranslationn

ElongationElongation

TerminationTermination

review

PolyribosomesPolyribosomes

Mutations