TranscriptionTranscriptionDNA DNA mRNA mRNA

ObjectivesObjectives Explain the purpose of transcription Explain the purpose of transcription

for a cellfor a cell Tell how RNA differs from DNATell how RNA differs from DNA Name the three main types of RNAName the three main types of RNA Describe the process of transcription Describe the process of transcription

ReviewReview What was the purpose for DNA replication?What was the purpose for DNA replication?

So cell division (mitosis & meiosis) can occur So cell division (mitosis & meiosis) can occur and each new cell created has a full set of DNAand each new cell created has a full set of DNA

What are the Nitrogen bases of DNA?What are the Nitrogen bases of DNA? A, G, C, TA, G, C, T

What is the sugar for DNA?What is the sugar for DNA? deoxyribosedeoxyribose

What does the structure of DNA allow?What does the structure of DNA allow? The strands are complementary of one The strands are complementary of one

another, meaning one strand is a template for another, meaning one strand is a template for the other.the other.

Central DogmaCentral Dogma Soon after there discovery Soon after there discovery

of DNA structure, Watson of DNA structure, Watson and Crick, stated that and Crick, stated that information in molecular information in molecular biology flows in one biology flows in one direction. From DNA to direction. From DNA to RNA to proteins.RNA to proteins.

The central dogma The central dogma involves three process: involves three process: Replication copies DNAReplication copies DNA Transcription converts a DNA Transcription converts a DNA

message into a temporary message into a temporary ‘disposable’ copy of DNA ‘disposable’ copy of DNA called RNAcalled RNA

Translation interprets an Translation interprets an RNA strand into a string of RNA strand into a string of Amino Acids which will turn Amino Acids which will turn into specific proteins.into specific proteins.

Transcription video

What is RNA?What is RNA?

3 main 3 main differences differences between DNA & between DNA & RNA?RNA?

RNA is like a “disposable RNA is like a “disposable copy” of a segment of DNA.copy” of a segment of DNA.

RNA consists of long chains of RNA consists of long chains of nucleotides (like DNA)nucleotides (like DNA) Parts of a Nucleotide:Parts of a Nucleotide:

5 carbon sugar5 carbon sugar Phosphate groupPhosphate group Nitrogenous baseNitrogenous base

RNA sugar- RNA sugar- RiboseRibose RNA is RNA is single strandedsingle stranded RNA contains RNA contains UracilUracil (U) in (U) in

place of Thymineplace of Thymine

Transcription makes 3 types of Transcription makes 3 types of RNARNA

Messenger RNA: mRNAMessenger RNA: mRNA

Ribosomal RNA: rRNARibosomal RNA: rRNA

Transfer RNA: tRNATransfer RNA: tRNA

Function of mRNA

• Carries copies of gene instructions for assembling amino acids into proteins from nucleus to ribosome (transcription)

Function of rRNAFunction of rRNA Forms part of ribosomes, a Forms part of ribosomes, a

cell’s protein factorycell’s protein factory

Large subunit binds to tRNA

Binding Sites

Small subunit binds to mRNA

Function of tRNAFunction of tRNA Brings amino acids from the Brings amino acids from the

cytoplasm to a ribosome to help cytoplasm to a ribosome to help make the growing proteinmake the growing protein

anticodon

Amino Acid

TranscriptionTranscription• TRANSCRIPTIONTRANSCRIPTION :The process of copying a :The process of copying a

sequence of DNA to produce a sequence of DNA to produce a complementary (disposable) strand of RNAcomplementary (disposable) strand of RNA

• During this process, a During this process, a GENE – not an entire GENE – not an entire chromosomechromosome – is transferred into an mRNA. – is transferred into an mRNA.

• The cell needs this process because DNA The cell needs this process because DNA has the information/code needed to make has the information/code needed to make proteins AND DNA is too valuable to leave proteins AND DNA is too valuable to leave the nucleus, so it makes a disposable copy!the nucleus, so it makes a disposable copy!

• THIS IS A MAJOR PART IN PROTEIN THIS IS A MAJOR PART IN PROTEIN SYNTHESIS!!!!! SYNTHESIS!!!!!

Overview of Protein Synthesis:

• Ribosomes are made in nucleolus

•Ribosomes leave through the Nuclear pores on the nuclear membrane

•Some attach to ER, while others remain free floating

•Ribosomes begin attaching Amino Acids together to form proteins

•Proteins enter into RER to be modified and folded (shaped) into structures

•Vesicles form from RER and carry proteins to Golgi apparatus

•There proteins are

packaged, sorted and/ or

stored in Golgi

•Once the proteins are

ready to leave, vesicles

form to transport proteins

throughout the cell and to

other cells.

What are genes?What are genes? Genes are coded Genes are coded

DNA DNA instructionsinstructions that that control the control the production of production of proteins within a cell.proteins within a cell. The code is held with The code is held with

the sequence of the sequence of nitrogen bases in nitrogen bases in DNA. Like credit card DNA. Like credit card numbers, unique to numbers, unique to every person!every person!

REMEMBER: that a REMEMBER: that a chromosome is chromosome is made up of multiple made up of multiple genes, and genes, and transcription only transcription only copies specific copies specific genes, 1 at a timegenes, 1 at a time..

Step 1:Step 1: RNA polymeraseRNA polymerase binds to promoters binds to promoters

on DNA strand and begins to unwind on DNA strand and begins to unwind a segment of DNA that corresponds a segment of DNA that corresponds to the gene it is copying.to the gene it is copying.

start site

nucleotides

transcription complex

Step 2:Step 2: RNA polymerase, using only one strand of DNA as a RNA polymerase, using only one strand of DNA as a

template, adds on free-floating RNA nucleotidetemplate, adds on free-floating RNA nucleotide As RNA polymerase moves along the DNA, a As RNA polymerase moves along the DNA, a

growing RNA strands hangs freely as it is growing RNA strands hangs freely as it is transcribed, and the DNA helix zips back together.transcribed, and the DNA helix zips back together.

*A - U, C – G there are NO T’s*A - U, C – G there are NO T’s

DNA

RNA polymerase moves along the DNA

Step 3Step 3:: Once the entire gene has been transcribed, Once the entire gene has been transcribed,

the RNA strand detaches completely from the the RNA strand detaches completely from the DNA.DNA.

Exactly how RNA polymerase recognizes the Exactly how RNA polymerase recognizes the end of a gene is very complicated but we will end of a gene is very complicated but we will discuss as it reaching a Stop signal.discuss as it reaching a Stop signal.

RNA polymeraseRNA polymerase• RNA polymerase is an enzyme that RNA polymerase is an enzyme that

plays multiple roles in transcription plays multiple roles in transcription processprocess

• Unzips the DNA molecule where gene is Unzips the DNA molecule where gene is foundfound

• Adds free floating nucleotides to make Adds free floating nucleotides to make mRNA strandmRNA strand

What it DOESN’T do is proof read it’s What it DOESN’T do is proof read it’s work like DNA polymerase.work like DNA polymerase.

How does RNA How does RNA polymerase know polymerase know

where to start and where to start and stop?stop?

Promoter sites-Promoter sites- which have specific which have specific nitrogen base nitrogen base sequences (TAC)sequences (TAC)

Promoters are Promoters are signals in DNA to signals in DNA to indicate where an indicate where an enzyme can bind to enzyme can bind to make RNAmake RNA

Stop signals/sitesStop signals/sites – – specific sequence of specific sequence of nitrogen bases that nitrogen bases that tell the RNA tell the RNA polymerase to stop polymerase to stop and fall off.and fall off.

replication

transcription

translation

growing RNA strands

DNA

onegene