Genes – Coding and FlankingGenes – Coding and Flanking

Genes are made up of different regions:Genes are made up of different regions:

– CodingCoding region – part that contains region – part that contains information for producing the proteininformation for producing the protein

– FlankingFlanking regions – the regions before regions – the regions before (upstream) and after (downstream) the (upstream) and after (downstream) the coding regioncoding region

Coding RegionsCoding Regions

Coding regions contains the Coding regions contains the information for producing the proteininformation for producing the protein

It is not a continuous piece of It is not a continuous piece of information but is interrupted by many information but is interrupted by many non-coding sequences called non-coding sequences called intronsintrons

The coding parts are called The coding parts are called exonsexons

Introns and ExonsIntrons and Exons

Flanking RegionsFlanking Regions

UpstreamUpstream – has an important role in – has an important role in starting the process of protein starting the process of protein production – has production – has promoterspromoters to which to which hormones can attachhormones can attach

DownstreamDownstream – this region is about 20 – this region is about 20 base pairs long and regulates gene base pairs long and regulates gene action by ending the transcription action by ending the transcription processprocess

Flanking regionsFlanking regions

Coding RegionUpstreamFlankingRegion

DownstreamFlankingRegion

RNARNAThere are 3 different types of RNA:There are 3 different types of RNA:

Messenger RNA (mRNA)Messenger RNA (mRNA) – copies and carries – copies and carries the genetic code from the DNA in the nucleus the genetic code from the DNA in the nucleus to the ribosomesto the ribosomes

Ribosomal RNA (rRNA)Ribosomal RNA (rRNA) – makes up – makes up ribosomes which are responsible for ribosomes which are responsible for assembling the proteins according to the assembling the proteins according to the instructions on mRNAinstructions on mRNA

Transfer RNA (tRNA)Transfer RNA (tRNA) – molecules which – molecules which carry the amino acids to the ribosomes carry the amino acids to the ribosomes where they are used to construct the proteinwhere they are used to construct the protein

Protein ProductionProtein Production1. 1. Transcription:Transcription: DNA code on DNA code on genes copied genes copied to mRNA to mRNA templatetemplate2. mRNA is 2. mRNA is able to pass able to pass through through nuclear pores nuclear pores and travel to and travel to ribosomesribosomes3. Translation:3. Translation: Amino acids Amino acids are carried to are carried to the ribosomes the ribosomes by tRNA where by tRNA where they are they are assembled into assembled into a polypeptide a polypeptide chain chain according to according to the mRNA the mRNA sequencesequence

A closer lookA closer lookhttp://207.207.4.198/pub/flash/26/transmenu_s.swf

http://www.wisc-online.com/objects/index_tj.asp?objID=AP1302

TranscriptionTranscription

An enzyme – An enzyme – RNA polymeraseRNA polymerase attaches attaches to a region of the DNA in the upstream to a region of the DNA in the upstream region of the gene that codes for the region of the gene that codes for the protein to be producedprotein to be producedDNA unravels and separates the two DNA unravels and separates the two strands of DNA, exposing one template strands of DNA, exposing one template strandstrandThe base sequence of the DNA The base sequence of the DNA template acts as a guide for the template acts as a guide for the building of a complementary copy of building of a complementary copy of messenger RNA (mRNA)messenger RNA (mRNA)

TranscriptionTranscriptionRNA polymerase moves along the DNA RNA polymerase moves along the DNA template as the mRNA strand is formedtemplate as the mRNA strand is formedThe resulting mRNA strand is called pre-The resulting mRNA strand is called pre-mRNA mRNA

TranscriptionTranscription

3’… A G T C C T A A G T A C G A T C …5’3’… A G T C C T A A G T A C G A T C …5’

5’… U C A _ _ _ _ _ _ _ _ _ _ U A C …3’5’… U C A _ _ _ _ _ _ _ _ _ _ U A C …3’

If this represents the sequence of bases on the

template DNA, what would the sequence of the mRNA

strand be?

DNA

mRNA

Remember: RNA compared with DNA is – single-stranded and contains uracil instead of thymine.

ModificationModification

Introns are excised from the pre-mRNAIntrons are excised from the pre-mRNA5’ and 3’ ends added5’ and 3’ ends added

ModificationModification

About 30% of About 30% of human genes are human genes are able to form more able to form more than one protein due than one protein due to to alternative alternative splicingsplicing of the pre- of the pre-mRNAmRNA– some of the introns some of the introns

are kept; or are kept; or – the order of exons is the order of exons is

altered in the final altered in the final mRNA copymRNA copy

TranslationTranslation

The modified mRNA exits the nucleus The modified mRNA exits the nucleus via the nuclear poresvia the nuclear poresOnce in the cytoplasm, it is able to Once in the cytoplasm, it is able to attach to the smaller subunit of the attach to the smaller subunit of the ribosome at the 5’ endribosome at the 5’ endThe mRNA is made up of triplets of The mRNA is made up of triplets of nucleotides called nucleotides called codonscodonsThe codons code for a particular amino The codons code for a particular amino acidacidThere are 22 amino acids in totalThere are 22 amino acids in total

Remember the ribosome itself is made up of ribosomal RNA (rRNA)

CodonsCodons

CodonsCodons

TranslationTranslation

The corresponding amino acid is The corresponding amino acid is brought to the codon on the mRNA at brought to the codon on the mRNA at the ribosome by the transfer RNA the ribosome by the transfer RNA molecules (tRNA)molecules (tRNA)

Transfer RNA

TranslationTranslation

The The tRNAtRNA attach to the mRNA via the attach to the mRNA via the anticodonanticodon on the tRNA molecule on the tRNA molecule

The anticodon is a sequence of The anticodon is a sequence of nucleotides which is complementary to nucleotides which is complementary to the codon on the mRNAthe codon on the mRNA

On the opposite end, the tRNA carries On the opposite end, the tRNA carries the amino acid for which the codon the amino acid for which the codon correspondscorresponds

TranslationTranslation

When two tRNA molecules are adjacent to When two tRNA molecules are adjacent to each other, the larger subunit of the each other, the larger subunit of the ribosome is able to form a peptide bond ribosome is able to form a peptide bond between the two amino acids that they carry, between the two amino acids that they carry, releasing the first of the tRNA moleculesreleasing the first of the tRNA moleculesWith each formation of a peptide bond, the With each formation of a peptide bond, the mRNA moves along the ribosome and the mRNA moves along the ribosome and the next tRNA molecule joinsnext tRNA molecule joinsThis process continues until all of the amino This process continues until all of the amino acids coded for by the mRNA are attached to acids coded for by the mRNA are attached to the polypeptide and the STOP codon is the polypeptide and the STOP codon is reachedreached

TranslationTranslationWhat do

A, B, C, D, E, and F

represent?

CodonsCodonsUsing this table, write the amino acid sequence coded for by the following mRNA sequence:

5’ AUG ACU GGU UUC GCC GAU AAA GAG GUG AAA CCA…

MET THR _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

In SummaryIn Summary

FeatureFeature DNADNA RNARNA

Sugar type in Sugar type in nucleotidenucleotide

Possible Possible bases found in bases found in nucleotidenucleotide

Usual Usual StructureStructure

Double- Double- stranded helixstranded helix

Complete the following table

In SummaryIn Summary

IngredientsIngredients JobJob

Nuclear DNANuclear DNA

mRNAmRNA

rRNArRNA

tRNAtRNA

RNA RNA polymerasepolymerase

Amino acidsAmino acids

Complete the following table