DNA Chapter 8. Every cell in your body has its own DNA that is identical to every other cell in your bodyEvery cell in your body has its own DNA that

DNADNAChapter 8Chapter 8

• Every cell in your body has Every cell in your body has its own DNA that is identical its own DNA that is identical to every other cell in your to every other cell in your bodybody

• Your DNA is different from Your DNA is different from everyone else’s DNA, unless everyone else’s DNA, unless you have an identical twinyou have an identical twin

• DNA is found inside the DNA is found inside the nucleus of every cell that has nucleus of every cell that has a nucleusa nucleus

• If a cell does not have a If a cell does not have a nucleus, DNA is found nucleus, DNA is found floating around in the floating around in the cytoplasmcytoplasm

• What we have been calling What we have been calling genes are really DNAgenes are really DNA

• Chromosomes are made up Chromosomes are made up of DNA of DNA

• DNA is short for DNA is short for ddeoxyriboeoxyribonnucleic ucleic aacidcid

• DNA is a molecule that DNA is a molecule that makes up genes and makes up genes and determines the traits of all determines the traits of all living thingsliving things

• ALL living things contain ALL living things contain DNADNA

• DNA is made up of units called DNA is made up of units called nucleotidesnucleotides

• A nucleotide consists of a A nucleotide consists of a nitrogenous basenitrogenous base, a , a phosphate phosphate groupgroup and a 5 carbon sugar and a 5 carbon sugar called called deoxyribosedeoxyribose (hence the (hence the name name deoxyribodeoxyribonucleic acid)nucleic acid)

• DNA looks very much like a DNA looks very much like a twisted laddertwisted ladder

• A ladder has two sides and A ladder has two sides and many rungsmany rungs

• The sides of DNA are made up The sides of DNA are made up of two different chemicals – a of two different chemicals – a sugar (deoxyribose) and an acid sugar (deoxyribose) and an acid (phosphate group)(phosphate group)

• The sugar and acid alternate The sugar and acid alternate on each side of the DNAon each side of the DNA

• The rungs of the DNA ladder The rungs of the DNA ladder are made up of chemicals are made up of chemicals called nitrogen basescalled nitrogen bases

• There are four different There are four different nitrogen bases in DNAnitrogen bases in DNA

• The 4 bases are adenine, The 4 bases are adenine, thymine, guanine & cytosinethymine, guanine & cytosine

• Adenine only fits with ThymineAdenine only fits with Thymine

• Cytosine only fits with GuanineCytosine only fits with Guanine

• There are only two bases on There are only two bases on each DNA rungeach DNA rung

• Adenine (A) & Guanine (G) are Adenine (A) & Guanine (G) are PurinesPurines

• Cytosine (C) & Thymine (T) are Cytosine (C) & Thymine (T) are PyrimidinesPyrimidines

• A Purine is A Purine is alwaysalways paired with a paired with a PyrimidinePyrimidine

• Purines are bigger than Purines are bigger than PyrimidinesPyrimidines

• Between each base pair are Between each base pair are hydrogen bondshydrogen bonds which hold which hold the two bases togetherthe two bases together

• The ladder of DNA is The ladder of DNA is twisted into a spiral, or helixtwisted into a spiral, or helix

• DNA is called a DNA is called a double helixdouble helix

• It is called a double helix It is called a double helix because it is made up of two because it is made up of two strands that are twistedstrands that are twisted

• Scientists did not know much Scientists did not know much about DNA until the 1900’s about DNA until the 1900’s

• Many different experiments Many different experiments provided info about DNA (8.1, provided info about DNA (8.1, pg 226-228)pg 226-228)

• The order of nitrogen The order of nitrogen bases in DNA is the code bases in DNA is the code for all your traitsfor all your traits

• If the order is changed in If the order is changed in any way, there will be a any way, there will be a different traitdifferent trait

• This works much the same This works much the same way as the Alphabetway as the Alphabet

• The word The word penpen means one means one thing, but if we change the E thing, but if we change the E to an I, it means something to an I, it means something totally differenttotally different

• If we change the P to an H, it If we change the P to an H, it means something elsemeans something else

• However, if we change the E However, if we change the E in pen to a D, the word in pen to a D, the word would make no sense at allwould make no sense at all

• It is the same with DNA – It is the same with DNA – sometimes changes make the sometimes changes make the DNA say something else, & DNA say something else, & sometimes it makes no sensesometimes it makes no sense

• When DNA is changed to make When DNA is changed to make no sense at all, it could mean no sense at all, it could mean death or a severe illnessdeath or a severe illness

• The difference is there are only The difference is there are only 4 letters in the DNA alphabet – 4 letters in the DNA alphabet – but the words are much longer but the words are much longer

Question 1Question 1• If one strand of DNA is: If one strand of DNA is:

A T G G C A T G CA T G G C A T G C

What is the other strand What is the other strand going to look like? going to look like?

Question 2Question 2•If one strand is: If one strand is:

G G C T A G A G A T G G C T A G A G A T

What is the other What is the other strand? strand?

DNA & ChromosomesDNA & Chromosomes• Prokaryotic cells lack a nucleus, Prokaryotic cells lack a nucleus,

so the DNA is located in the so the DNA is located in the cytoplasmcytoplasm

• Prokaryotes have one circular Prokaryotes have one circular “chromosome” that contains “chromosome” that contains most or all of the cells DNAmost or all of the cells DNA

• Eukaryotic cells have at least Eukaryotic cells have at least 1000 times as much DNA as 1000 times as much DNA as prokaryotic cellsprokaryotic cells

• Eukaryotic DNA is not free in Eukaryotic DNA is not free in the cytoplasm, but is in the the cytoplasm, but is in the nucleusnucleus

• The number of chromosomes The number of chromosomes varies in eukaryotesvaries in eukaryotes

Size & Length of DNASize & Length of DNA

• DNA molecules are VERY longDNA molecules are VERY long

• E. coliE. coli DNA is 4,639,221 base DNA is 4,639,221 base pairs long = approx. 1.6mmpairs long = approx. 1.6mm

• An An E. coliE. coli cell is only 1.6 cell is only 1.6m! m!

• The DNA must fit in a space one The DNA must fit in a space one one-thousandth of its length! one-thousandth of its length!

Chromosome StructureChromosome Structure

• The DNA must be folded The DNA must be folded numerous times to fit into the numerous times to fit into the cell’s nucleuscell’s nucleus

• A human cell contains almost A human cell contains almost 1000 times as many base pairs 1000 times as many base pairs as as E. coli – E. coli – human DNA must be human DNA must be folded even more!folded even more!

• Eukaryotic chromosomes Eukaryotic chromosomes contain protein & DNA (form a contain protein & DNA (form a substance called substance called chromatinchromatin))

• The DNA is tightly coiled The DNA is tightly coiled around proteins called around proteins called histoneshistones

• The DNA & histones form a The DNA & histones form a nucleosomenucleosome

• Nucleosomes coil together to Nucleosomes coil together to form a thick fiber and form a thick fiber and supercoilssupercoils

• The supercoils form a The supercoils form a chromosomechromosome

• We saw chromosomes in We saw chromosomes in Chapter 5 (figure 5.5)Chapter 5 (figure 5.5)

DNA ReplicationDNA Replication

• DNA must be replicated before DNA must be replicated before mitosis (and meiosis)mitosis (and meiosis)

• How does that occur? How does that occur?

• Each strand of DNA has the Each strand of DNA has the info to make the other strand info to make the other strand (B/C of base pairing)(B/C of base pairing)

• During DNA replication, the During DNA replication, the DNA molecule separates into DNA molecule separates into two strands, then produces two two strands, then produces two new new complimentarycomplimentary strands strands following the rules of base following the rules of base pairingpairing

• In eukaryotes, DNA replication In eukaryotes, DNA replication occurs in numerous places on occurs in numerous places on the DNAthe DNA

• The place where the DNA is The place where the DNA is opening and replication is opening and replication is occurring is called the occurring is called the replication forkreplication fork

• An important enzyme that helps An important enzyme that helps in DNA replication is called in DNA replication is called DNA PolymeraseDNA Polymerase

• There are other enzymes that There are other enzymes that “unzip” the DNA and then zip “unzip” the DNA and then zip the new strands back up againthe new strands back up again

RNA & Protein RNA & Protein SynthesisSynthesis

Chapter 8.4 & 8.5Chapter 8.4 & 8.5

How does DNA code for traits? How does DNA code for traits?

• DNA must remain in the DNA must remain in the nucleus – it is too fragile, & too nucleus – it is too fragile, & too important to be in the important to be in the cytoplasmcytoplasm

• DNA codes for proteins, but DNA codes for proteins, but proteins are made in the proteins are made in the cytoplasmcytoplasm

• How can this be? How can this be? • DNA has a helper molecule DNA has a helper molecule

to leave the nucleus and go to leave the nucleus and go into the cytoplasm to make into the cytoplasm to make proteinsproteins

• This molecule is ribonucleic This molecule is ribonucleic acid – or acid – or RNARNA

RNA StructureRNA Structure

• RNA is similar to DNA in RNA is similar to DNA in that it is made of nucleotidesthat it is made of nucleotides

• There is no Thymine in RNA There is no Thymine in RNA – instead there is a base – instead there is a base called Uracil (U), which is called Uracil (U), which is similar to thyminesimilar to thymine


• RNA is single stranded, not RNA is single stranded, not double stranded (not a double stranded (not a double helix) double helix)

• The sugar in RNA is ribose, The sugar in RNA is ribose, not deoxyribosenot deoxyribose


• You can think of RNA as a You can think of RNA as a disposable copy of DNA or a disposable copy of DNA or a working copy of a single geneworking copy of a single gene

• One gene on DNA can make One gene on DNA can make hundreds or thousands of RNA hundreds or thousands of RNA copies of that gene, which can in copies of that gene, which can in turn make that many proteinsturn make that many proteins

Types of RNATypes of RNA

• There are 3 types of RNA, each There are 3 types of RNA, each with a specific structure and with a specific structure and functionfunction

• Messenger RNAMessenger RNA (mRNA) is the (mRNA) is the copy of the DNAcopy of the DNA

• Ribosomal RNARibosomal RNA (rRNA) makes (rRNA) makes up the ribosomesup the ribosomes

Types of RNATypes of RNA

• Transfer RNATransfer RNA (tRNA) is (tRNA) is used in the making of used in the making of proteins and brings the proteins and brings the amino acids to the amino acids to the ribosomeribosome

Making ProteinsMaking Proteins

• There are two main stages of There are two main stages of making proteins – making proteins – Transcription & TranslationTranscription & Translation

• TranscriptionTranscription is going from is going from DNA to RNADNA to RNA

• TranslationTranslation is going from RNA is going from RNA to proteinto protein

TranscriptionTranscription

• Transcription occurs in the Transcription occurs in the nucleusnucleus

• RNA polymerase is an enzyme RNA polymerase is an enzyme that is needed, similar to DNA that is needed, similar to DNA polymerasepolymerase

• Only one strand of DNA is used Only one strand of DNA is used to make RNAto make RNA


• Transcription is similar to DNA Transcription is similar to DNA replication, but the result is replication, but the result is single stranded with Uracils in single stranded with Uracils in the place of Thyminesthe place of Thymines

• The resulting RNA will be The resulting RNA will be complimentary to the DNA complimentary to the DNA strand usedstrand used


• RNA polymerase knows where RNA polymerase knows where genes start because of pieces of genes start because of pieces of DNA called DNA called promoterspromoters

• Promoters have specific base Promoters have specific base sequences – they act as signals sequences – they act as signals to the RNA polymeraseto the RNA polymerase


• Similar pieces of DNA act as Similar pieces of DNA act as signals for the RNA polymerase signals for the RNA polymerase to stop transcriptionto stop transcription

• The RNA made from The RNA made from transcription needs to be edited transcription needs to be edited before usebefore use


• Large pieces of RNA will be cut Large pieces of RNA will be cut out, called out, called intronsintrons

• The remaining pieces of RNA The remaining pieces of RNA are called are called exonsexons and are spliced and are spliced back together with enzymesback together with enzymes

The Genetic CodeThe Genetic Code

• Proteins are made by joining Proteins are made by joining amino acidsamino acids together together

• How can an mRNA molecule How can an mRNA molecule make a protein if RNA is make a protein if RNA is made of nucleotides? made of nucleotides?


• The genetic code has only four The genetic code has only four letters (A,U,G,C)letters (A,U,G,C)

• But, each word in the code is But, each word in the code is three letters longthree letters long

• Each three letter word makes a Each three letter word makes a specific amino acidspecific amino acid


• The 3-letter words are called The 3-letter words are called codonscodons

• For instance, the codon For instance, the codon AUGAUG always codes for the amino acid always codes for the amino acid methioninemethionine


• The mRNA sequence The mRNA sequence AUGGCGUGU can be broken AUGGCGUGU can be broken up into its codonsup into its codons

• AUG – GCG – UGU AUG – GCG – UGU

• The amino acid sequence is:The amino acid sequence is:–methionine, alanine, cysteinemethionine, alanine, cysteine


• Figure 8.13 shows the genetic Figure 8.13 shows the genetic code (page 244)code (page 244)

• Here are some other Genetic Here are some other Genetic Code chartsCode charts

• (You will have this on a test)(You will have this on a test)

TranslationTranslation

•TranslationTranslation occurs occurs outside of the outside of the nucleus, in the nucleus, in the cytoplasm of the cell, cytoplasm of the cell, on the Ribosomeon the Ribosome


• Translation requires the 3 Translation requires the 3 types of RNAtypes of RNA

• mRNA = messenger RNAmRNA = messenger RNA

• tRNA = transfer RNAtRNA = transfer RNA

• rRNA = ribosomal RNArRNA = ribosomal RNA


• Attached to each tRNA is an Attached to each tRNA is an Amino AcidAmino Acid

• Amino acids make up the poly-Amino acids make up the poly-peptidespeptides

• There is also an There is also an anti-codonanti-codon on on the tRNAthe tRNA

TranslationTranslation• The anti-codon on the tRNA The anti-codon on the tRNA

matches up with the codon on matches up with the codon on the mRNAthe mRNA

Translation – Step by StepTranslation – Step by Step

• First, the mRNA must be First, the mRNA must be transcribed from the DNA, transcribed from the DNA, leave the nucleus & go to the leave the nucleus & go to the cytoplasmcytoplasm

• Then, the mRNA attaches to a Then, the mRNA attaches to a ribosome in the cytoplasmribosome in the cytoplasm


• The mRNA moves through the The mRNA moves through the ribosome in ribosome in one directionone direction & for & for each codon, the proper each codon, the proper amino acidamino acid is attached to the polypeptide is attached to the polypeptide chain via the tRNAchain via the tRNA

• The The anti-codonanti-codon on the tRNA on the tRNA matches up with the matches up with the codoncodon on the on the mRNAmRNA


• For example – the start codon For example – the start codon on the mRNA is A U Gon the mRNA is A U G

• The anti-codon is U A CThe anti-codon is U A C

• Then, a second tRNA with the Then, a second tRNA with the next amino acid attaches to a next amino acid attaches to a different site on the ribosomedifferent site on the ribosome


• The ribosome forms a peptide The ribosome forms a peptide bond between the 1bond between the 1stst and 2 and 2ndnd amino acidamino acid

• The bond between the 1The bond between the 1stst tRNA tRNA and its amino acid is brokenand its amino acid is broken

• The ribosome then moves to the The ribosome then moves to the 33rdrd codon codon


• The polypeptide continues to The polypeptide continues to grow in this fashion until the grow in this fashion until the ribosome reaches a stop codon ribosome reaches a stop codon (UAA, UAG or UGA)(UAA, UAG or UGA)

• The mRNA molecule is then The mRNA molecule is then released & the polypeptide is released & the polypeptide is released into the cytoplasmreleased into the cytoplasm

Genes and ProteinsGenes and Proteins

• The polypeptide made in The polypeptide made in translation will be modified by translation will be modified by the golgi or the rough ER and the golgi or the rough ER and made into a fully functional made into a fully functional proteinprotein

• Proteins control almost Proteins control almost everything that living cells do! everything that living cells do!


• Why is it important that the Why is it important that the mRNA is read in one direction mRNA is read in one direction only? only?

• Decode the following Decode the following DNADNA strand from left to right strand from left to right GACAAGTCCACAATCGACAAGTCCACAATC


• The mRNA strand is: The mRNA strand is: CUGUUCAGGUGUUAGCUGUUCAGGUGUUAG

• The amino acid sequence is The amino acid sequence is leucine-phenylalanine-leucine-phenylalanine-arginine-cysteine-stoparginine-cysteine-stop


• Now, read the mRNA strand Now, read the mRNA strand right to left right to left GAUUGUGGACUUGUCGAUUGUGGACUUGUC

• The amino acid sequence is The amino acid sequence is aspartic acid-cysteine-aspartic acid-cysteine-glycine-leucine-valineglycine-leucine-valine


• The resulting proteins are The resulting proteins are completely different and will do completely different and will do different things – maybe even different things – maybe even not function at all! not function at all!

• Next, we’ll talk about mutations Next, we’ll talk about mutations and how they affect proteins and how they affect proteins and traitsand traits

MutationsMutations

• Every now and then cells make Every now and then cells make a mistake in copying DNA or a mistake in copying DNA or making RNAmaking RNA

• These mistakes are called These mistakes are called mutationsmutations

• Mutations come in all “shapes Mutations come in all “shapes & sizes”& sizes”

MutationsMutations

• Gene mutations result from Gene mutations result from changes in a single genechanges in a single gene

• Chromosomal mutations Chromosomal mutations involve changes in a whole involve changes in a whole chromosomechromosome

MutationsMutations

• Most gene mutations involve Most gene mutations involve just one nucleotide, but some just one nucleotide, but some involve manyinvolve many

• Mutations that affect only one Mutations that affect only one nucleotide are called nucleotide are called point point mutationsmutations

MutationsMutations

• When one nucleotide is switched When one nucleotide is switched out for another, it will generally out for another, it will generally change only one amino acid in change only one amino acid in the protein the protein

• If one nucleotide is inserted or If one nucleotide is inserted or deleted, more severe changes deleted, more severe changes occuroccur

MutationsMutations

• Mutations that add or delete a Mutations that add or delete a nucleotide are called nucleotide are called frame-shift frame-shift mutationsmutations

• They affect every amino acid They affect every amino acid after the mutation – very badafter the mutation – very bad

• HOW???HOW???

Example - substitutionExample - substitution

• DNA: TCT DNA: TCT AACA ACC ACGCA ACC ACG

• RNA: ??RNA: ??

• Amino Acid: ??Amino Acid: ??

• New DNA: TCTNew DNA: TCTTTCAACCACGCAACCACG

• NEW RNA: ??NEW RNA: ??

• New Amino Acids: ??New Amino Acids: ??

Example - substitutionExample - substitution

• DNA: TCT ACA ACC ACGDNA: TCT ACA ACC ACG

• RNA: AGA UGU UGG UGCRNA: AGA UGU UGG UGC

• Amino Acid: arginine – cysteine Amino Acid: arginine – cysteine – tryptophan – cysteine – tryptophan – cysteine

NEWNEW

• DNA: TCT DNA: TCT TTCA ACC ACGCA ACC ACG

• RNA: AGA RNA: AGA AAGU UGG UGCGU UGG UGC

• Amino Acids: arginine – Amino Acids: arginine – serineserine – tryptophan – cysteine – tryptophan – cysteine

Example - DeletionExample - Deletion

• DNA: TTCGTCATGCACATCDNA: TTCGTCATGCACATC

• RNA = ??RNA = ??

• Amino Acids = ??Amino Acids = ??

• New DNA: TTCGTCTGCACATCNew DNA: TTCGTCTGCACATC

• New RNA = ??New RNA = ??

• New Amino Acids = ??New Amino Acids = ??

Example - DeletionExample - Deletion

• DNA: TTCGTCDNA: TTCGTCAATGCACATCTGCACATC

• RNA: AAG CAG UAC GUG RNA: AAG CAG UAC GUG UAGUAG

• Amino Acids: lysine-glutamine-Amino Acids: lysine-glutamine-tyrosine-valine-stoptyrosine-valine-stop

NEWNEW

• DNA: TTCGTCTGCACATCDNA: TTCGTCTGCACATC

• RNA: AAG CAG ACG UGU RNA: AAG CAG ACG UGU AGAG

• Amino Acids: lysine-glutamine-Amino Acids: lysine-glutamine-threonine-cysteine-…threonine-cysteine-…

Chromosomal MutationsChromosomal Mutations

• There are different types of There are different types of chromosomal mutationschromosomal mutations

• A A deletiondeletion is when part of the is when part of the chromosome is deletedchromosome is deleted

• A A duplicationduplication is when a part pf is when a part pf the chromosome is duplicatedthe chromosome is duplicated

Chromosomal MutationsChromosomal Mutations

• An An inversioninversion is when parts of a is when parts of a chromosome are switched chromosome are switched aroundaround

• A A translocationtranslocation is when pieces is when pieces of one chromosome end up on a of one chromosome end up on a different chromosomedifferent chromosome

Documents

DNA Chapter 8. Every cell in your body has its own DNA that is identical to every other cell in your bodyEvery cell in your body has its own DNA that