DNA To RNA To Proteins

Foothill High School Science DepartmentFoothill High School Science Department

DNA To RNA To ProteinsDNA To RNA To Proteins

Transcription, Translation → ProteinsWhich is

The Central Dogma of Biology

Transcription, Translation → ProteinsWhich is

The Central Dogma of Biology


The Structure of RNAThe Structure of RNA

• Long Chains of NucleotidesLong Chains of Nucleotides– 5 Carbon Sugar ( Ribose )5 Carbon Sugar ( Ribose )– Phosphate GroupPhosphate Group– Nitrogenous BaseNitrogenous Base

• A, G, C, U ( no T )A, G, C, U ( no T )

– Single StrandedSingle Stranded


Types of RNATypes of RNA

RNA Mostly For Protein SynthesisRNA Mostly For Protein Synthesis

Three Types of RNAThree Types of RNA

Messenger RNA, Messenger RNA, mRNAmRNA

Ribosomal RNA, Ribosomal RNA, rRNArRNA

Transfer RNA, Transfer RNA, tRNAtRNA


Types of RNATypes of RNA

mRNAmRNAA Copy of the Recipe in the DNA. Transports the A Copy of the Recipe in the DNA. Transports the

Recipe to the Ribosome.Recipe to the Ribosome.

rRNArRNAPart of ribosome.Part of ribosome.

It Reads the Recipe in the It Reads the Recipe in the mRNAmRNAPuts the ingredients togetherPuts the ingredients together

tRNAtRNATransports Amino Acids (the ingredients) from Transports Amino Acids (the ingredients) from

cytoplasm to the Ribosomes in the Order cytoplasm to the Ribosomes in the Order Needed to make the Protein (the Cookies)Needed to make the Protein (the Cookies)


Transcription (mRNAmRNA)Transcription (mRNAmRNA)

The process of copying the DNA The process of copying the DNA nucleotide sequence into a nucleotide sequence into a

complementary sequence of RNAcomplementary sequence of RNA

( ( copying the recipecopying the recipe))

Requires a special enzyme:Requires a special enzyme:

RNA PolymeraseRNA Polymerase(Transcription Rate= ~60 nucleotides/second)(Transcription Rate= ~60 nucleotides/second)


RNA PolymeraseRNA Polymerase

DNA

RNARNAPolymerasePolymerase

DNA


TranscriptionTranscription

Key ConceptKey Concept:

During transcription, RNA During transcription, RNA polymerase binds to DNA and polymerase binds to DNA and separates the DNA strands. RNA separates the DNA strands. RNA Polymerase then uses one strand Polymerase then uses one strand of DNA as a template to of DNA as a template to assemble nucleotides into RNAassemble nucleotides into RNA


TranscriptionTranscription

PromotersPromoters– Regions on DNA that show where

RNA PolymeraseRNA Polymerase must bind to begin the Transcription of RNA

– Specific base sequences act as signals

– Other base sequences indicate stopping points


TranscriptionThe Devil is in the Details


RNA SplicingRNA SplicingAfter the DNA is transcribed into After the DNA is transcribed into

mRNA:mRNA:Editing must be done to the mRNA Editing must be done to the mRNA chain to make the mRNA functionalchain to make the mRNA functional




Introns Introns need to be removedneed to be removed

• These are non-functional segments of the These are non-functional segments of the mRNA strand copied from the DNAmRNA strand copied from the DNA

• Snipped out of the chain in the nucleusSnipped out of the chain in the nucleus

ExonsExons need to be glued back togetherneed to be glued back together

• These segments contain the real recipe and These segments contain the real recipe and need to be reconnected to make the real, need to be reconnected to make the real, functional mRNAfunctional mRNA

This Process is called: This Process is called: mRNA SplicingmRNA Splicing


mRNA SplicingmRNA Splicing


The Genetic CodeThe Genetic Code

Proteins areProteins are::

– long chains of amino acids.long chains of amino acids.• There are 20 different amino acidsThere are 20 different amino acids

– The order of amino acids in the The order of amino acids in the protein determine its shape and protein determine its shape and functionfunction


There are There are 20 amino acids20 amino acids but only but only 4 bases4 bases in RNA. in RNA.

So, How Can You Design A Code?So, How Can You Design A Code?

AdenineAdenine AACytosineCytosine CCGuanine Guanine GGUracil Uracil UU


RNARNABasesBases



The genetic code consists of The genetic code consists of “words” three bases long“words” three bases long

Each “word” is called aEach “word” is called a Codon:Codon:A codon is three consecutive A codon is three consecutive nucleotides that code for a single nucleotides that code for a single

amino acidamino acid



For ExampleFor Example::

UCGUCGCACCACGGUGGU = RNA Sequence= RNA Sequence

UCG UCG - - CAC CAC -- GGUGGU = = CodonsCodons

UCGUCG codes for Serinecodes for SerineCACCAC codes for Histidinecodes for HistidineGGUGGU codes for Glycinecodes for Glycine



If you have 4 Bases and….If you have 4 Bases and….CodonsCodons are defined with 3 Bases…..are defined with 3 Bases…..

How many combinations of 3 can you make?How many combinations of 3 can you make?

There Are 64 Possible 3-base codonsThere Are 64 Possible 3-base codons

Since there are only 20 amino acids,Since there are only 20 amino acids,some amino acids are represented by some amino acids are represented by

multiple codonsmultiple codons


Code WheelCode Wheel

Table On Page 303


Code TableCode Table


8 Essential Amino Acids8 Essential Amino Acids

Essential AA Meats Grains Legumes

MethionineMethionine TryptophanTryptophan

PhenylalaninePhenylalanine LeucineLeucine

ThreonineThreonine ValineValine

IsoleucineIsoleucine LysineLysine

Essential AA = An Amino Acid That Can NOT Be Made, It Must Be EatenEssential AA = An Amino Acid That Can NOT Be Made, It Must Be Eaten


TranslationTranslation

TranslationTranslation is the process of is the process of decoding the mRNA and chaining decoding the mRNA and chaining

Amino Acids together into the Amino Acids together into the polypeptide chainpolypeptide chain(making the protein)(making the protein)

(See pages 245-247)(See pages 245-247)

• RibosomesRibosomes– Read mRNA and construct the proteinsRead mRNA and construct the proteins


Translation Step ATranslation Step A


Translation Step BTranslation Step B


Translation Step CTranslation Step C

Step C– Ribosome connects the Ribosome connects the

amino acids together as amino acids together as they come into the they come into the ribosomeribosome

– Ribosome disconnects Ribosome disconnects the the 3the the 3rdrd amino acid amino acid from the ribosome to from the ribosome to float into the cytoplasmfloat into the cytoplasm


Translation Step DTranslation Step D

• Step DStep D– Polypeptide chain Polypeptide chain

grows until the grows until the mRNA STOP Codon mRNA STOP Codon is reachedis reached

– The ribosome then The ribosome then releases the releases the polypeptide chain polypeptide chain into the cytoplasminto the cytoplasm


The Roles of DNA & RNAThe Roles of DNA & RNA

DNADNA = = The CookbookThe Cookbook

mRNAmRNA = = A copy of the A copy of the

recipe from “The recipe from “The Cookbook”Cookbook”


Genes & ProteinsGenes & Proteins

• Genes are instructions for Genes are instructions for assembling proteins assembling proteins (recipes in a cookbook)(recipes in a cookbook)

• Proteins Proteins (the cookies from the recipe)(the cookies from the recipe) are are enzymes that catalyze and regulate enzymes that catalyze and regulate chemical reactionschemical reactions– Pigments, antigens, regulatorsPigments, antigens, regulators

– Proteins are the keys to biological Proteins are the keys to biological functionfunction

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DNA To RNA To Proteins