RNA and Protein RNA and Protein SynthesisSynthesis

What is a gene?What is a gene?

A region of DNA that A region of DNA that contains instructions contains instructions for the making of for the making of proteins.proteins.

chromosomeschromosomes::

fibers of DNA (chromatin) and proteins

contains all genetic information for cell on genesenes

• genes contain information for synthesis of proteins

• DNA is blueprint for organization, development, daily functioning of cell.

RNARNARibonucleic acidRibonucleic acidFunctionFunction: moves the : moves the genetic information from genetic information from DNA in the nucleus to the DNA in the nucleus to the ribosome (site of protein ribosome (site of protein synthesis) in the synthesis) in the cytoplasmcytoplasm

RRNA StructureNA Structure Formed by nucleotidesFormed by nucleotides

Sugar – RiboseSugar – RibosePhosphate groupPhosphate groupNitrogenous BaseNitrogenous Base

AdenineAdenineUracil (replaces thymine)Uracil (replaces thymine)CytosineCytosineGuanine Guanine

Single-strandedSingle-stranded

3 types of RNA3 types of RNA

Messenger RNA Messenger RNA (mRNA)(mRNA)

Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)

Transfer RNA (tRNA)Transfer RNA (tRNA)

Messenger RNA Messenger RNA (mRNA)(mRNA)

Structure – single strandStructure – single strandFunction – carries Function – carries genetic information from genetic information from DNA in nucleus to the DNA in nucleus to the ribosomeribosome

Location - nucleusLocation - nucleus

Rules of base-pairing apply for the mRNA

DNA mRNA

- A- T- G- C- T- A

U -A -C -G -A -U -

A always with UC always with G

Making of the Mobile MessengerMaking of the Mobile Messenger

Piece of DNA that has information to make a specific protein

RNA must be “complementarycomplementary” to DNA

Ribosomal RNA Ribosomal RNA (rRNA)(rRNA)

Structure – globularStructure – globularFunction – makes up Function – makes up the ribosomethe ribosome

Location – ribosomeLocation – ribosome

rRNA = rRNA = ribosomal RNAribosomal RNA

”structural structural work-benchwork-bench” on which proteins are built

Transfer RNA (tRNA)Transfer RNA (tRNA)Shape – hairpin (t-shaped)Shape – hairpin (t-shaped)Function – carries Function – carries (transfers) amino acid to (transfers) amino acid to ribosomeribosome

Location – cytoplasm to Location – cytoplasm to ribosomeribosome

tRNA = transfer RNAtRNA = transfer RNA

1. picks up one one specificspecific amino amino acidacid AND

2. pairs with mRNA codonmRNA codon specific for that amino acid only!

Protein SynthesisProtein Synthesis

2 stages2 stagesTranscription in Transcription in the nucleusthe nucleus

Translation in the Translation in the ribosomeribosome

Transcription + Translation:Transcription + Translation:

Nucleus

RNA Protein

Cytoplasm

DNA

TRANSCRIPTION TRANSLATION

TranscriptionTranscription

Transferring Transferring information from DNA information from DNA to mRNAto mRNA

CodonCodon3 bases of mRNA 3 bases of mRNA nucleotidesnucleotides

Each Each codoncodon codes for a codes for a specific amino acidspecific amino acid

Near universal – supports Near universal – supports idea that organisms are idea that organisms are relatedrelated

CodonsCodonsStart CodonStart Codon – AUG – AUGStop CodonsStop Codons – UAA, – UAA, UAG, UGAUAG, UGA

These codons tell These codons tell translation to begin translation to begin and endand end

AnticodonAnticodon3 bases of tRNA 3 bases of tRNA nucleotidesnucleotides

Complementary to Complementary to mRNA codonmRNA codon

Located on opposite end Located on opposite end of amino acidof amino acid

RibosomeRibosome

Composed of rRNA with 3 Composed of rRNA with 3 binding sitesbinding sites

Free in cytoplasm – proteins Free in cytoplasm – proteins are used in the cellare used in the cell

RER – makes proteins to be RER – makes proteins to be exported out of the cellexported out of the cell

DNA vs. RNADNA vs. RNADNADNA

5 Carbon Sugar = 5 Carbon Sugar = DeoxyriboseDeoxyribose

Base Pairs = Base Pairs = AdenineAdenine

ThymineThymine

GuanineGuanine

CytocineCytocine Original copy of Original copy of

genetic informationgenetic information

RNARNA 5 Carbon Sugar = 5 Carbon Sugar =

RiboseRibose Base Pairs = Base Pairs =

AdenineAdenine

UracilUracil

GuanineGuanine

CytocineCytocine Disposable copy of Disposable copy of

genetic genetic informationinformation

ribosome “reads” mRNA codons one at a time

mRNAmRNA codonscodons ... C G C A A G C C C U G U

proteinprotein =

G C G

arginine lysine

U U C

proline

G G G

cysteine

A C AANTICODONSANTICODONS

How About An How About An Example?Example?

DNA: TGG CCA ATA mRNA: ACC GGU UAU

tRNA: UGG CCA AUA

ACC= 20 GGU=12 UAU=13Code for an Amino Acid Sequence!

Example = Hairy

Steps for Translation:Steps for Translation:1. mRNA leaves nucleus to cytoplasm - codons specify certain AA sequence

2. mRNA associates with ribosome which “reads” mRNA codons one at a time• synthesis of proteins occur on ribosomes

3. tRNA with specific amino acid (corresponding to anticodon) carries correct amino acid to mRNA + ribosomes

4. tRNA delivers correct amino acid (anticodon-codon base pairing) to ribosome and leaves

5. polypeptide elongates in sequence directed by the mRNA codons formation of peptide bond between amino acids

6. termination reached at stop codon ribosome falls off polypeptide is released

TranscriptionTranscriptionExons – coding regions Exons – coding regions of DNAof DNA

Introns – non-coding Introns – non-coding regions of DNAregions of DNA

Cut out (spliced) which controls Cut out (spliced) which controls the genetic information that the genetic information that leaves the nucleusleaves the nucleus