RNA and TranscriptionRNA and Transcription

DNA and Protein SynthesisDNA and Protein Synthesis

Coding for GenesCoding for Genes

GeneGene are coded DNA instructions that are coded DNA instructions that control the production of proteins within control the production of proteins within the cellthe cell

The first step is to copy a part of the The first step is to copy a part of the nucleotide sequence from DNA into nucleotide sequence from DNA into RNARNA

RNARNA

RNA RNA ribonucleic acid, nucleotideribonucleic acid, nucleotide Sugar Sugar Ribose Ribose Single strandedSingle stranded Contains the nitrogenous base Contains the nitrogenous base Uracil (U)Uracil (U)

rather than Thyminerather than Thymine

Types of RNATypes of RNA

Main job is Main job is Protein SynthesisProtein Synthesis the the assembly of amino acids into proteinsassembly of amino acids into proteins

Messenger RNAMessenger RNA Ribosomal RNARibosomal RNA Transfer RNATransfer RNA

Messenger RNA (mRNA)Messenger RNA (mRNA)

Most genes contain Most genes contain instructions for instructions for assembly amino acids assembly amino acids into proteins and into proteins and messenger RNA messenger RNA carries copies of carries copies of those instructionsthose instructions

Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)

Proteins are Proteins are assembled on assembled on ribosomesribosomes

Ribosomes contain Ribosomes contain rRNArRNA

Transfer RNA (tRNA)Transfer RNA (tRNA)

Transfers each amino Transfers each amino acid to the ribosome acid to the ribosome as it is specified by as it is specified by coded messages of coded messages of mRNAmRNA

TranscriptionTranscription

RNA molecules are produced by copying part of RNA molecules are produced by copying part of the nucleotide sequence of DNA into a the nucleotide sequence of DNA into a complementary sequence of RNA. This process complementary sequence of RNA. This process is called is called TranscriptionTranscription

Requires Requires RNA PolymeraseRNA Polymerase (enzyme) (enzyme) RNA polymerase binds to DNA and separates RNA polymerase binds to DNA and separates

the DNA strands. RNA polymerase then uses the DNA strands. RNA polymerase then uses one strand of DNA as a template from which one strand of DNA as a template from which nucleotides are assembled into a strand of RNAnucleotides are assembled into a strand of RNA

TranscriptionTranscription

RNA polymerase will only bind to certain RNA polymerase will only bind to certain spots on the DNA molecule, called spots on the DNA molecule, called promoterspromoters. (have a specific base . (have a specific base sequence)sequence) Promoters are signals in DNA that indicate to Promoters are signals in DNA that indicate to

the enzyme where to bind to make RNAthe enzyme where to bind to make RNA

RNA editingRNA editing

RNA molecules require some editing RNA molecules require some editing before they can be usedbefore they can be used

DNA of eukaryotic genes contain DNA of eukaryotic genes contain sequences of nucleotides called sequences of nucleotides called intronsintrons, , that are not involved in coding for proteinsthat are not involved in coding for proteins

The DNA sequences that code for proteins The DNA sequences that code for proteins are called are called exonsexons because they are because they are “expressed”.“expressed”.

RNA editingRNA editing

RNA editingRNA editing

When RNA molecules are formed from the When RNA molecules are formed from the copied DNA, introns are cut out of the copied DNA, introns are cut out of the RNA while in the nucleus.RNA while in the nucleus.

The remaining exons are spliced together The remaining exons are spliced together to make the final mRNAto make the final mRNA

Genetic CodeGenetic Code

Proteins are made by joining amino acids Proteins are made by joining amino acids into long chains called into long chains called polypeptidespolypeptides..

Each polypeptide contains a combination Each polypeptide contains a combination of any or all of the 20 different amino of any or all of the 20 different amino acids. This is how the properties of acids. This is how the properties of proteins are determined.proteins are determined.

Genetic CodeGenetic Code

RNA contains the bases, A U C G (letters) RNA contains the bases, A U C G (letters) and this is what the “code” consists of.and this is what the “code” consists of.

The genetic code is read three letters at a The genetic code is read three letters at a time, so that each “word” of the coded time, so that each “word” of the coded message is three bases long.message is three bases long.

Each three-letter “word” in mRNA is known Each three-letter “word” in mRNA is known as a as a codoncodon. .

CodonsCodons

A codon consists of 3 A codon consists of 3 consecutive consecutive nucleotides that nucleotides that specify a single amino specify a single amino acid that is to be acid that is to be added to the added to the polypeptide.polypeptide.

CodonsCodons

Example:Example:

UCGCACGGUUCGCACGGU

UCG-CAC-UCG-CAC-GGUGGU

Ser- Hist- GlySer- Hist- Gly

CodonsCodons

AUG AUG Methionine or “START” codon Methionine or “START” codon UAA, UAG, UGA UAA, UAG, UGA “STOP” codons, that “STOP” codons, that

signify the end of a polypeptidesignify the end of a polypeptide

PracticePractice

T A C C C A T T G G A G T C G A T TT A C C C A T T G G A G T C G A T T

A U G G G U A A C C U C A G C U A AA U G G G U A A C C U C A G C U A A AUG – GGU- AAC – CUC – AGC - UAAAUG – GGU- AAC – CUC – AGC - UAA

MET – GLY – ASP – LEU – ARG - STOPMET – GLY – ASP – LEU – ARG - STOP

YOU TRY!!YOU TRY!!

DNA:DNA:

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