genes – coding and flanking genes are made up of different regions: –coding region – part that...
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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