TranscriptionTranscription

The Central Dogma of The Central Dogma of Molecular Biology:Molecular Biology:DNA------>RNA------DNA------>RNA------

>Protein>Protein The central dogma The central dogma

concerns the flow of concerns the flow of biological biological information: information: DNA is a self-DNA is a self-

replicating molecule replicating molecule containing genetic containing genetic information that can information that can be transcribed into be transcribed into an RNA message that an RNA message that can be translated can be translated into a polypeptide into a polypeptide (protein).(protein).

DNADNA The DNA molecule is a The DNA molecule is a

double helix of two double helix of two long chains of long chains of nucleotide molecules. nucleotide molecules.

During DNA During DNA replication DNA is replication DNA is duplicated, producing duplicated, producing two double helices.two double helices.

Imbedded in these Imbedded in these long strands of DNA long strands of DNA are genes that control are genes that control the production of the production of proteins to the cell.proteins to the cell.

TranscriptionTranscription

The first step in The first step in decoding these genetic decoding these genetic messages is to copy part messages is to copy part of the genetic sequence of the genetic sequence from DNA into RNA, or from DNA into RNA, or ribonucleic acid. This is ribonucleic acid. This is called called TranscriptionTranscription

These RNA molecules These RNA molecules then carry out the then carry out the process of making process of making proteins.proteins.

Structure of Structure of RNARNA

RNA, like DNA, RNA, like DNA, consists of a long consists of a long chain of chain of nucleotides. nucleotides.

The structure of The structure of RNA and DNA RNA and DNA nucleotides are nucleotides are very similar.very similar.

Structure of RNAStructure of RNA There are three distinct There are three distinct

differences;differences; The sugar in RNA is ribose The sugar in RNA is ribose

(two hydroxyl groups)(two hydroxyl groups) RNA is generally single RNA is generally single

strandedstranded RNA contains the RNA contains the

nitrogenous base Uracil in nitrogenous base Uracil in place of Thymineplace of Thymine

RNA is like a copy of a RNA is like a copy of a master blue print (DNA) master blue print (DNA) that is used to create that is used to create the building blocks of the building blocks of the cell.the cell.

Types of RNA:Types of RNA: RNA molecules have many RNA molecules have many

functions, but most RNA is used functions, but most RNA is used in the process of protein in the process of protein synthesis.synthesis.

The assembly of amino acids into The assembly of amino acids into proteins is controlled by RNA.proteins is controlled by RNA.

Types of RNATypes of RNA

The three major The three major types of RNA are:types of RNA are:

Messenger RNA Messenger RNA (mRNA)(mRNA)

Ribosomal RNA Ribosomal RNA (rRNA)(rRNA)

Transfer RNA Transfer RNA (tRNA)(tRNA)

Messenger RNA (mRNA)Messenger RNA (mRNA) Most genes contain Most genes contain

instructions for instructions for assembling amino assembling amino acids into proteins.acids into proteins.

The RNA molecules The RNA molecules that carry copies of that carry copies of these instructions are these instructions are known as messenger known as messenger RNA (mRNA) because RNA (mRNA) because they serve as the they serve as the messenger from DNA messenger from DNA to the rest of the cell.to the rest of the cell.

Ribosomal RNA (rRNA)Ribosomal RNA (rRNA)

Proteins are Proteins are assembled on assembled on ribosomes.ribosomes.

Ribosomes are Ribosomes are made of proteins made of proteins as well as a form as well as a form of RNA known of RNA known as Ribosomal as Ribosomal RNA (rRNA).RNA (rRNA).

Transfer RNA (tRNA)Transfer RNA (tRNA) During the During the

construction of construction of proteins, a third type proteins, a third type of RNA molecule of RNA molecule transfers each amino transfers each amino acid to the ribosomes acid to the ribosomes as it is specified by as it is specified by coded messages in coded messages in the mRNA.the mRNA.

These RNA molecules These RNA molecules are known as are known as Transfer RNA Transfer RNA (tRNA).(tRNA).

TranscriptionTranscription

RNA molecules RNA molecules are produced by are produced by copying copying (transcribing) part (transcribing) part of the nucleotide of the nucleotide sequence of DNA sequence of DNA into into complimentary complimentary sequence of RNA. sequence of RNA. This is called This is called TRANSCRIPTION.TRANSCRIPTION.

TranscriptionTranscription Transcription requires Transcription requires

an enzyme known as an enzyme known as RNA polymerase that is RNA polymerase that is similar to DNA similar to DNA polymerase.polymerase.

During transcription, During transcription, RNA polymerase binds RNA polymerase binds to DNA and separates to DNA and separates the DNA strands.the DNA strands.

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

TranscriptionTranscription How does RNA How does RNA

polymerase know polymerase know where to start and where to start and stop?stop?

RNA polymerase will RNA polymerase will only bind to DNA in only bind to DNA in an area called the an area called the promoter region, promoter region, which have specific which have specific base sequences. base sequences.

There are also non-There are also non-coding regions of DNA coding regions of DNA called termination called termination sequences which tell sequences which tell RNA polymerase to RNA polymerase to stop transcribing.stop transcribing.

RNA EditingRNA Editing

RNA requires RNA requires editing, just like editing, just like most of your most of your papers.papers.

Large pieces of Large pieces of RNA are RNA are sometimes cut and sometimes cut and trimmed before trimmed before they can go into they can go into action (only in action (only in eukaryotes).eukaryotes).

RNA EditingRNA Editing The pieces removed The pieces removed

are called are called intronsintrons (intervening (intervening sequences) and are sequences) and are cut out why the cut out why the RNA is still inside RNA is still inside the nucleus.the nucleus.

The remaining The remaining portions, called portions, called exonsexons, or expressed , or expressed sequences, are sequences, are spliced back spliced back together to form together to form the final mRNA.the final mRNA.

RNA EditingRNA Editing Why do cells spend Why do cells spend

valuable energy to valuable energy to make long strands of make long strands of RNA just to cut them RNA just to cut them up and splice them up and splice them back together?back together?

This is done so RNA This is done so RNA can be cut and spliced can be cut and spliced in different ways so a in different ways so a single gene can be single gene can be used to produce many used to produce many different RNA strands.different RNA strands.