Chapter 12: DNA and RNA
The Components and Structure of DNA
 DNA – deoxyribonucleic acid
 Deoxyribose – simple sugar in DNA
 DNA is made up of nucleotides
 Nucleotide – made of simple sugar, phosphate and a nitrogen base
 4 Nitrogen Bases in DNA
1. adenine
purines – double ring
2. guanine
3. cytosine
pyrimidines – single ring
4. thymine





Nucleotides join together to form long chains
Phosphate and deoxyribose form the backbone of the chain (sides of the ladder)
Nitrogen bases for the steps of the ladder
The amount of adenine equals thymine
The amount of guanine equals cytosine
Phosphate
Deoxyribose
Hydrogen Bond
Nitrogen Base
Nucleotide
History of DNA
 Rosalind Franklin and Maurice Wilkins worked on the structure of DNA based on xray crystallography (pictures of DNA by x-rays).
 James Watson and Francis Crick were also working on the structure of DNA
 These scientists were trying to be the first to discover and prove the structure of
DNA because they knew it would be one of the most important discoveries in the
20th century.
 1953 Watson and Crick proposed that DNA is made of two chains of nucleotides
joined together by nitrogen bases
 two bases are held together by hydrogen bond
 two strands are complementary
 complementary base pairing
 A and T
 C and G
 DNA is shaped in a double helix
A-A-G-C-T-T-G-C-C-A-T-C-A-G-T-G-G-A-C-G-T-A-C-C-G-T-
The Importance of Nucleotide Sequences
 All living organisms are composed of A, T, C, G
 How can organisms be so different from each other if their genetic material is made
of the same four nucleotides?
 Differences in organisms are from the sequence of the four different nucleotides
and how many nucleotides
 The closer the relationship between two organisms the greater the similarity in
their order of DNA nucleotides
 Scientists use nucleotide sequences to determine evolutionary relationships among
organisms
 Nucleotide sequences can also be used to determine whether two people are
related
 DNA from a crime scene matches the DNA of a suspected criminal
DNA and Chromosomes
 Eukaryotic DNA is found in the nucleus in the form of a number of chromosomes
 DNA molecules are very long.
 Human cell contains more than 1 meter of DNA
 How is so much DNA folded into tiny chromosomes?
 Chromatin – DNA that is tightly coiled around proteins
 Histones – proteins DNA is wrapped around
 Nucleosome – two wraps of DNA around a histone
Replication of DNA
 Before a cell can divide by mitosis or meiosis it must first make a copy of its
chromosomes
 DNA Replication – DNA is copied
 All organisms undergo replication
How DNA Replicates
 During replication each strand serves as a pattern to make a new DNA molecule
 The end result is the formation of two DNA molecules that are identical (duplicated
chromosome)
 Steps of Replication
1. Enzyme, DNA helicase, breaks the hydrogen bonds between nucleotides, this
“unzips” the DNA molecule
2. Free nucleotides from the surroundings in the nucleus bond to the single strands.
Enzyme, DNA polymerase glues the new strands together.
3. This continues until the entire molecule has been unzipped and replicated
4. Each new strand formed is a complement of one of the originals or parent strand.
5. Two DNA molecules that are identical
 DNA molecule consists of two opposing DNA strands
 DNA consists of a 3’  5’ template strand and a 5’  3’ template strand
 Enzyme, DNA polymerase, moves in the 3’  5’ direction along each template
strand.
 It can only assemble nucleotides in the 3’  5’ direction
 The new, complement strand grows in the 5’  3’ direction
 3’  5’ template strand replication occurs fast as DNA polymerase follows the
replication fork assembling a 5’  3’ complementary strand.
 This strand is called the leading strand.
 5’  3’ template strand, DNA polymerase moves away from uncoiling replication
fork.
 DNA polymerase assembles short segments of nucleotides away from the
replication fork.
 After each segment is assembles DNA polymerase returns to replication fork to
begin assembling next segment.
 Okazaki Segments – short segments of complementary DNA
 Lagging Strand – it takes more time to assemble.
 DNA Ligase – enzyme that connects Okazaki segments to produce a single
complementary strand
11.2 From DNA to Proteins
Genes and Proteins
 Proteins form and become key cell structures and regulators of cell functions
 Sequence of amino acid makes specific proteins
 The sequence of nucleotides in each gene contains information for assembling
amino acids.
 It is estimated that each human cell contains about 80,000 genes
RNA
 RNA – ribonucleic acid
 3 Differences Between DNA and RNA
RNA
DNA
Single Stranded
Double Stranded
Sugar is Ribose
Sugar is Deoxyribose
Adenine, Guanine, Cytosine, Uracil
Adenine, Guanine, Cytosine, Thymine
RNA can leave the nucleus
DNA can not leave the nucleus
DNA - A-C-G-T-G-A-A-G-C-T-G-T-A-C-A-G-T-C-A-G-G-C-T-A
RNA  What is the role of RNA in the cell:
 DNA provides workers with the instructions for making the proteins
 RNA takes the DNA instructions on how a protein is made then amino acid by
amino acid they assemble the protein.
 3 Types of RNA that help to build proteins
1. Messenger RNA (mRNA) – brings information from the DNA in the nucleus to the
cytoplasm
2. Ribosomal RNA (rRNA) – what ribosomes are made of and they clamp onto the
mRNA and use its information to assemble amino acids
3. Transfer RNA (tRNA) – transports amino acids to the ribosome to be assembled
into a protein.
Transcription
 Transcription – enzymes make an RNA copy of a portion of a DNA strand
 The process of transcription is similar to replication except
 transcription results in single strand of RNA
 Does not transcribe the entire strand of DNA
 Steps of Transcription From DNA to RNA
1. The process of transcription begins as enzymes, RNA polymerase, unzips the
molecule of DNA
2. As the DNA molecule unzips, RNA polymerase assembles RNA nucleotides
using one strand of the DNA as a template.
3. Only the 3’  5’ template strand of DNA is transcribed. The RNA complimentary
strand grows in the 5’  3’ direction.
4. Transcription continues until RNA polymerase reaches a special sequence of
nucleotides.
5. mRNA molecule breaks away and mRNA leaves the nucleus and enters the
cytoplasm.
The Genetic Code
 Proteins are built from amino acids
 20 different amino acids
 Codon – each set of 3 nitrogen bases represents an amino acid, which is also called
a triplet code
 The order of nitrogen bases in DNA can determine the type and order of amino acids
in a protein
 64 different combinations
 61 code for amino acids
 3 signal to stop protein synthesis
 more than 1 codon can code for the same amino acid
 Codons represent the same amino acids in all organisms
 Gives evidence of evolution
 Start codon is AUG (methionine)
 Stop codons are UAA, UAG, UGA
Translation From mRNA to Protein
 Translation – the process of converting the information in a sequence of nitrogen
bases in mRNA into a sequence of amino acids
 Takes place at the ribosomes in the cytoplasm
The Role of Transfer RNA
 To bring the amino acids to the ribosome
 Correct translation of the mRNA message depends upon the joining of each mRNA
codon with the correct tRNA molecule
 tRNA recognizes the mRNA codon, because tRNA has a sequence of three
nucleotides that are complement of the nucleotides in the codon
 Anti-Codon – tRNA nucleotides
 Ex: mRNA – A-C-A
tRNA – U-G-U
DNA
T–A–C–A–G–G –T–C–G –T–T–A–C–G–G–A–C–T
mRNA
tRNA
Amino
Acids
Translating the mRNA Code
 Steps of Translation
1. The first codon of the mRNA strand attaches to a ribosome
2. tRNA molecules, each carrying a specific amino acid approach the
ribosome
3. tRNA anticodon pairs with mRNA codon
4. The first codon on mRNA is AUG which codes for amino acid methionine.
AUG is the start codon for protein synthesis.
5. A new tRNA molecule carrying an amino acid will pair with the mRNA
codon
6. As the process continues a chain of amino acids is formed until the
ribosome reaches a stop codon on the mRNA strand UAA, UAG, UGA.
12-4 Mutations
Mutation: A Change in DNA
 Mutation – any change in the DNA sequence that also changes the protein it codes
for
 Mutations in Reproductive Cells
 If mutation occurs in egg or sperm the altered gene would become part of the
genetic makeup of the offspring
 Sometimes the mutation is so severe that the embryo does not survive
 In rare cases a gene mutation may have positive effects
 Mutations in Body Cells
 If the cells DNA is changed this mutation would not be passed on to offspring
 But the mutations can cause harm to the individual
2 Types of Mutations in DNA
1. Point Mutation
 Is a change in a single base pair in DNA
 A change in a single letter changes the meaning of this sentence
2. Frameshift Mutation
 A mutation in which a single base is added or deleted from DNA
 This mutation would cause nearly every amino acid in the protein after the
deletion to be changed.
Chromosomal Mutations
 Chromosomal Mutations – changes in chromosomes during replication. Parts can
be broken or lost.
 They occur in all living organisms, but they are especially common in plants
 Although rare, changes in an organisms chromosome structure do occur.
 Chromosomal mutations are rarely passed on to the next generation because:
 The zygote usually dies
 The mature organism is usually sterile
 4 Types of Chromosomal Mutations
1. Deletion – a fragment of a chromosome breaks off, it can be lost when a
cell divides
2. Duplication – the chromosome fragment attaches to its homologous
chromosome, which will then carry two copies of a certain set of genes.
3. Inversion – fragment reattaches to the original chromosome in the reverse
orientation.
4. Translocation – a fragment may join a nonhomologous chromosome.
Causes of Mutations
 Spontaneous Mutations – a mistake in base pairing during DNA replication. It
occurs at random or at any given moment.
 Mutagen – any agent that can cause a change in DNA
 Ex. Chemicals, radiation, high temperatures
Repairing DNA
 When mistakes do occur repair mechanisms fix mutations
 Proofreading enzymes – reads the DNA strand and checks it for mistakes
 Repair enzymes – fixes any mistakes in the DNA strand
Mistakes in Meiosis
 Sometimes accidents occur during meiosis and chromosomes fail to separate
correctly
 Nondisjunction – failure of homologous chromosomes to separate
 During meiosis I one chromosome from each pair is supposed to move to opposite
poles but occasionally both chromosomes of a pair move to the same pole
 Trisomy – 1 extra chromosome (47)
 Ex: extra chromosome on pair number 21 – down syndrome
 Monosomy – missing 1 chromosome (45)
 Ex: missing chromosome on pair number 23 – turner syndrome
 Tetraploid – 2 extra chromosomes (48)
 Polyploids – organisms with more than the usual number of chromosome sets
 Is rare in animals and almost always results in death.
Chapter 12: DNA and RNA
The Components and Structure of DNA
 DNA –
 Deoxyribose –
 DNA is made up of _______________
 Nucleotide –
 4 Nitrogen Bases in DNA
1.
purines –
2.
3.
pyrimidines –
4.
 Nucleotides join together to form long chains
 _______________ and _______________ form the backbone of the chain (sides of
the ladder
 ____________ ____________ are the steps of the ladder
 The amount of _______________ equals _______________
 The amount of _______________ equals _______________
History of DNA
 Rosalind Franklin and Maurice Wilkins worked on the structure of DNA based on xray crystallography (pictures of DNA by x-rays).
 James Watson and Francis Crick were also working on the structure of DNA
 These scientists were trying to be the first to discover and prove the structure of
DNA because they knew it would be one of the most important discoveries in the
20th century.
 1953 Watson and Crick proposed that DNA is made of two chains of nucleotides
joined together by nitrogen bases


 complementary base pairing


 DNA is shaped like a ____________ ____________
DNA
A – A –G –C –T –T –G –C –C –A –T –C –A –G –T –G –G –A –C
The Importance of Nucleotide Sequences

 How can organisms be so different from each other if their genetic material is made
of the same four nucleotides?
 Differences in organisms are from the _______________ of the four different
nucleotides and how _______________ nucleotides
 The closer the relationship between two organisms the greater the similarity in
their order of DNA nucleotides
 Scientists use nucleotide sequences to determine _______________
_______________
 Nucleotide sequences can also be used to determine whether two people are
_______________

DNA and Chromosomes
 Eukaryotic DNA is found in the nucleus in the form of a number of chromosomes
 DNA molecules are very long
 Human cell contains more than _____ meter of DNA
 How is so much DNA folded into tiny chromosomes?
 Chromatin –
 Histones –
 Nucleosome –
Replication of DNA
 Before a cell can divide by mitosis or meiosis it must first make a copy of its
chromosomes
 DNA Replication –
 All organisms undergo replication
How DNA Replicates
 During replication each strand serves as a pattern to make a new DNA molecule
 The end result is the formation of 2 DNA molecules that are _______________
(duplicated chromosome)
 Steps of Replication
1. Enzyme _______ ____________, breaks the hydrogen bonds between
nucleotides, this “__________” the DNA molecule
2. Free _______________ from the surroundings in the nucleus bond to the single
strands. Enzyme, _______ ____________ glues the new strands together.
3. This continues until the entire molecule has been unzipped and replicated.
4. Each new strand formed is a _______________ of one of the originals or parent
strand.
5. Two DNA molecules are ________________
 DNA molecule consists of two opposing DNA strands
 DNA consists of a _______________ template strand and a _______________
template strand.
 Enzyme, _______ _______________, moves in the _______________ direction
along each template strand.
 It can only assemble nucleotides in the _______________ direction
 The new complement strand grows in the _______________ direction.
 _______________ template strand replication occurs fast as DNA polymerase
follows the _______________ _______________ assembling a ______________
complementary strand.
 _______________ template strand, DNA polymerase moves away from uncoiling
replication fork.
 DNA polymerase assembles short segments of nucleotides away from the
replication fork.
 After each segment is assembled DNA polymerase returns to replication fork to
begin assembling next segment.
 Okazaki Segments –
 Lagging Strand –
 DNA Ligase –
11.2 From DNA to Proteins
Genes and Proteins
 Proteins form and become key cell structures and regulators of cell functions

 The sequence of _______________ in each gene contains information for
assembling amino acids
 It is estimated that each human cell contains about 80,000 genes
RNA
 RNA –
 4 Differences Between DNA and RNA
RNA
DNA
DNA
A –C –G –T –G –A –A –G –C –T –G –T –A –C –A –G –T –C –A –G –G
RNA
 What is the role of RNA in the cell:
 DNA provides workers with the _______________ for making the ___________
 RNA takes the DNA instructions on how a protein is made then __________
__________ by amino acid they assemble the protein
 3 Types of RNA that help to build proteins
1. Messenger RNA (mRNA) –
2. Ribosomal RNA (rRNA) –
3. Transfer RNA (tRNA) –
Transcription
 Transcription –
 The process of transcription is similar to replication except


 Steps of Transcription From DNA to RNA
1. The process of transcription begins as enzyme, _______ _______________
unzips the molecule of DNA
2. As the DNA molecule unzips, _______ _______________ assembles RNA
nucleotides using _______ strand of the DNA as a template.
3.
Only the __________ template strand of DNA is transcribed. The RNA
complimentary strand grows in the __________ direction.
4. Transcription continues until RNA polymerase reaches a special sequence of
nucleotides
5. ________ molecule breaks away and the ________ leaves the nucleus and
enters the cytoplasm.
The Genetic Code
 Proteins are built from __________ __________
 _______ different amino acids
 Codon –
 The order of nitrogen bases in DNA can determine the type and order of amino acids
in a protein
 64 different combinations



 Codons represent the same amino acids in all organisms

 Start codon is __________
 Stop codons are __________, __________, __________
Translation From mRNA to Protein
 Translation –

The Role of Transfer RNA

 Correct translation of the mRNA message depends upon the joining of each mRNA
codon with the correct tRNA molecule
 tRNA recognizes the mRNA codon, because tRNA has a sequence of three
nucleotides that are complement of the nucleotides in the codon
 Anti-Codon –
 Ex: mRNA – A-C-A
tRNA –
DNA
mRNA
tRNA
Amino
Acids
T–A–C–A–G–G –T–C–G –T–T–A–C–G–G–A–C–T
Translating the mRNA Code
 Steps of Translation
1.
The first __________ of the mRNA strand attaches to a ribosome
2. __________ molecules, each carrying a specific __________ __________
approach the ribosome.
3. tRNA ____________ pairs with mRNA ____________
4. The first codon on mRNA is ________ which codes for amino acid
_______________. AUG is the start codon for protein synthesis.
5. A new __________ molecule carrying an amino acid will pair with the mRNA
codon.
6. As the process continues a chain of amino acids is formed until the ribosome
reaches a __________ condon on the mRNA strand, ________, ________,
________
12-4 Mutations
Mutation: A Change in DNA
 Mutation –
 Mutations in Reproductive Cells
 If mutation occurs in egg or sperm the altered gene would become part of the
genetic makeup of the offspring
 Sometimes the mutations is so severe that the embryo does not __________
 In rare cases a gene mutation may have positive effects
 Mutations in Body Cells
 If the cells DNA is changed this mutation would

2 Types of Mutations in DNA
1. Point Mutation


2. Frameshift Mutation


This mutation would cause nearly every amino acid in the protein after the
deletion to be changed. The same effect would also result from the addition
of a single base.
DNA Mutations
Chromosomal Mutations
 Chromosomal Mutations –
 They occur in all living organisms, but they are especially common in
_______________
 Although rare, changes in an organisms chromosome structure do occur
 Chromosomal mutations are rarely passed on to the next generation because:


 4 Types of Chromosomal Mutations
1. Deletion –
2. Duplication –
3. Inversion –
4. Translocation –
Causes of Mutations
 Spontaneous Mutations –
 Mutagen –
 Ex.
Repairing DNA
 When mistakes do occur repair mechanisms fix mutations
 Proofreading enzymes –
 Repair enzymes –
Mistakes in Meiosis
 Sometimes accidents occur during meiosis and chromosomes fail to separate
correctly
 Nondisjunction –
 During meiosis I one chromosome from each pair is supposed to move to opposite
poles but occasionally both chromosomes of a pair move to the same pole
 Trisomy –
 Ex:
 Monosomy –
 Ex:
 Tetraploid –
 Polyploids –
