A2 Edexcel Biology Session 4.7 Transcription.pptx

Session 4.7

Unit 4: Development, Plants and the EnvironmentTopic 6: Infections, immunity and forensics

TranscriptionIntroduction

Structure of a geneTranscription process

Splicing of exons

A2 Edexcel Biology Xavier DANIEL, Ph.D.

Session 4.7

Splicing of exons

DNA ReplicationDNA content doubles

TranscriptionSynthesis of RNAA region of DNA is used to make one RNA

TranslationSynthesis of proteinOne mRNA is used to make one protein

The Central Dogma of Molecular Biology

Introduction

Structure of RNA

Sugar-phosphate backbone

Adenine (A)

Cytosine (C)

Phosphate

Guanine (G)

Ribose

5’ end

Nitrogen bases

3’ end

Uracil (U)

One RNA strand

“single-stranded RNA”

Introduction

mRNA = Messenger RNAUsed as a template for protein synthesisIntermediate between DNA and proteinBrings the “message” written in DNA

Message = instructions for synthesizing the protein

tRNA = Transfer RNAUsed for protein synthesis

Brings amino acids

rRNA = Ribosomal RNAPart of Ribosomes

Introduction

mRNAs, tRNAs and rRNAs are used in translation

There are many kinds of RNA

For expression of genes and beyond

Regulation: siRNA, microRNA, snRNA Coding RNA: messenger RNA=mRNA Non-coding RNA: Tools in translation tRNA rRNA

Transcription takes place in the nucleusRNA is exported from the nucleus into the cytoplasmTranslation of mRNA takes place in the cytoplasm

TRANSCRIPTION

TRANSLATION

mRNARibosome

Protein

There is no nucleus,Transcription AND translation take place in the cytoplasm

Prokaryotes

Pre-mRNA

Nuclearenvelope

TRANSLATION

TRANSCRIPTION

MATURATION

Ribosome

Polypeptide

Eukaryotes

Introduction

Session 4.7

Splicing of exons

Structure of a gene

Contains the bases that encode the amino acids of

the protein

Inactive/ActiveActivated only if specific

transcription factors bind these base pairs

Contains the base pairs that make transcription

"Wait my signal before you start reading!"

"read the information!" "Stop reading!"

Session 4.7

Splicing of exons

Gene 1

Gene 2

Gene 3

DNA strand(template)

TRANSCRIPTION

TRADUCTION

Several RNA:- ribosomal- transfer- small nuclear- micro- messenger

Complementary

DNA RNA

A U T A G C C G

Complementarity

Overall direction

Transcription process

Transcription is the use of a region of one strand of the DNA double helix as a template to produce a molecule of RNA

This strand is called the non-coding strand/antisense strandOther strand = coding strand/sense strand/non-template strand

Enzyme: RNA Polymerase

RNA Polymerase adds AMP, CMP, GMP and UMP to a new RNA strand

AMP = Adenosine monophosphate

From the 5’P to the 3’OH end of the new RNA strandFrom the 3’OH to the 5’P end of the template DNA strand

The RNA strand is complementary to its DNA template

DNA RNATranscription

5' 3'aatgtagtagtaaactggtgaaatgcaaggtatttattgctaaggaagatgctggagattacatcatcatttgaccactttacgttccataaataacgattcgttctacgacctct3’ 5’

2. Transcribe the DNA coding strand only to RNA from 5’ to 3’ of the RNA

5' 3'aatgtagtagtaaactggtgaaatgcaaggtatttattgctaaggaagatgctggaga

1 Denaturation 5' 3'aatgtagtagtaaactggtgaaatgcaaggtatttattgctaaggaagatgctggaga

ttacatcatcatttgaccactttacgttccataaataacgattcgttctacgacctct3’ 5’

Non-coding strandAntisense strandTemplate strand

5’a 3’

Coding strandSense strandNon-template strand

Manual Transcription of DNA to RNA

5’aa 3’

5’aau 3’

5’aauguag 3’

Direction of transcription5’ to 3’ of RNA3’ to 5’ of coding/sense/non-template strand5’ to 3’ of non-coding/antisense/template strand

DNA RNA

5' 3'aauguaguaguaaacuggugaaaugcaagguauuuauugcuaaggaagaugcuggaga

RNA is almost the same as the coding/sense/non-template strand (U instead of T)RNA is complementary to the non-coding/antisense/template strand (CG GC / TA AU

Template DNA

Result of DNA Replication

Result of transcription

5' 3'aauguaguaguaaacuggugaaaugcaagguauuuauugcuaaggaagaugcuggaga

Comparison of DNA Replication and Transcription

Old DNANew DNA

Non-template / Coding Template / Non-coding

Not individual tRNAs hereRather… if you could put all the anticodons in tandem

Session 4.7

Splicing of exons

“Splicing” = joining two linear pieces together

Most eukaryotic genes are discontinuous The coding region of the gene is composed of two elements

- Exons = used in final/mature mRNA - Introns = NOT present in final/mature mRNA

But both exons and introns are present in the initial/immature mRNA

Introns will be “eliminated” / spliced outExons will be spliced together

Mature mRNA is composed of exons only

Only exons contains the codons

Only exons are coding for proteins This modification of pre-mRNA into mRNA happens after transcription

“Post-transcriptional modification”

Splicing of exons

Alternative splicing

Human body can make antibodies that are- embedded in the membrane of Lymphocyte sB- secreted by lymphocytes B

Two forms of the same proteins making up antibodies

Splicing of exons

Alternative splicing

Human genome contains less than 30 000 genes

Human body can produce 10 billions of different antibodies

Several mechanisms to increase the number of antibodiesOne is alternative splicing

A2 Edexcel Biology Session 4.7 Transcription.pptx

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