Chapter 11 DNAChapter 11 DNA

Within the structure of DNA is the Within the structure of DNA is the

information for life- the complete information for life- the complete

instructions for manufacturing all the instructions for manufacturing all the

proteinsproteins for an organism. for an organism. DNA 15min DNA 15min video.asfvideo.asf

DNA is a DNA is a polymerpolymer made of repeating made of repeating

subunits called nucleotides. subunits called nucleotides.

Nucleotides have three parts:Nucleotides have three parts:

simple sugarsimple sugar, , phosphate groupphosphate group & a & a

nitrogenous basenitrogenous base. .

DNA polymerDNA polymer known as CGCGTTTTCGCG known as CGCGTTTTCGCG

The simple sugar in DNA, called deoxyribose, The simple sugar in DNA, called deoxyribose,

gives DNA is name:gives DNA is name:

deoxyribose nucleic aciddeoxyribose nucleic acid..

The phosphate group is composed of an atom of The phosphate group is composed of an atom of phosphorousphosphorous surrounded by 4 surrounded by 4 oxygenoxygen atoms. atoms.

A A nitrogenous basenitrogenous base is a carbon is a carbon ringring structure that structure that contains one or more atoms of nitrogen. contains one or more atoms of nitrogen.

In DNA there are four possible nitrogen bases: In DNA there are four possible nitrogen bases: adenine (Aadenine (A), ), guanine (Gguanine (G), ), cytosine (ccytosine (c), and ), and thymine (Tthymine (T).).

Replication of DNAReplication of DNA

The DNA in the chromosomes is copied in a The DNA in the chromosomes is copied in a process called process called DNA replicationDNA replication. Without . Without DNA replication, new cells would have DNA replication, new cells would have only 1/2 of the DNA of their parents.only 1/2 of the DNA of their parents.

During replication, each strand serves as a During replication, each strand serves as a

pattern, or pattern, or templatetemplate, to make a new molecule. , to make a new molecule.

Replication begins as an enzymeReplication begins as an enzyme

that breaks the that breaks the hydrogenhydrogen bonds between bonds between

bases that hold the two strands together,bases that hold the two strands together,

thus “unzipping” DNA.thus “unzipping” DNA.

Genes & ProteinsGenes & Proteins

The sequence of The sequence of nucleotidesnucleotides in DNA in DNA

contains information. This information is put contains information. This information is put

to work through the production of to work through the production of proteinsproteins..

RNARNARNA, like DNA, is a RNA, like DNA, is a nucleic acidnucleic acid. .

However they differ in three ways:However they differ in three ways:

1.1. RNA is a single strand – DNA is doubleRNA is a single strand – DNA is double

2. RNA’s sugar is ribose – DNA’s sugar is 2. RNA’s sugar is ribose – DNA’s sugar is deoxyribose.deoxyribose.

3. Both RNA & DNA have 4 nitrogenous bases, 3. Both RNA & DNA have 4 nitrogenous bases, but rather than thymine, RNA contains a but rather than thymine, RNA contains a similar base called uracilsimilar base called uracil

RNA RNA vsvs DNA half min DNA half min video.asfvideo.asf

If DNA is what provides “workers” with If DNA is what provides “workers” with the instructions for making the proteins- the instructions for making the proteins-

what does RNA do?what does RNA do?

RNA is the workers for protein synthesis- RNA is the workers for protein synthesis-

they take DNA instructions on how the they take DNA instructions on how the

protein should be assembled then, amino protein should be assembled then, amino

acid by amino acid, they assemble the acid by amino acid, they assemble the

protein.protein.

What are the three types of RNA and What are the three types of RNA and what do they do?what do they do?

1.1. mRNA – messenger – brings instructions from mRNA – messenger – brings instructions from the DNA in the nucleus to the cells cytoplasm the DNA in the nucleus to the cells cytoplasm and then it moves it to a ribosome.and then it moves it to a ribosome.

2. rRNA – ribosomal – binds to the mRNA and 2. rRNA – ribosomal – binds to the mRNA and uses the instructions to assemble the amino uses the instructions to assemble the amino acids in the correct order.acids in the correct order.

3. tRNA – transfer – delivers amino acids to the 3. tRNA – transfer – delivers amino acids to the ribosome to be assembled into a protein.ribosome to be assembled into a protein.

The diagram below shows a ribosome attach to mRNA, and then move along the mRNA adding amino acids to the growing polypeptide chain.                                                                                  

TranscriptionTranscription

In the nucleus, enzymes make an RNA copy In the nucleus, enzymes make an RNA copy

of a portion of the of a portion of the DNA strandDNA strand in a process in a process

called called transcriptiontranscription..

The main difference between The main difference between transcription and DNA replicationtranscription and DNA replication : :

Transcription results in the formation of one Transcription results in the formation of one

single-stranded RNA molecule rather than single-stranded RNA molecule rather than

a double-stranded DNA molecule.a double-stranded DNA molecule.

Genetic CodeGenetic Code

The nucleotide sequence transcribed from The nucleotide sequence transcribed from

DNA to a strand of messenger RNA acts as DNA to a strand of messenger RNA acts as

a genetic a genetic messagemessage, the complete , the complete

information for the building of a protein information for the building of a protein

TranslationTranslation

The process of The process of convertingconverting the information in the information in

a sequence of nitrogenous bases in mRNA a sequence of nitrogenous bases in mRNA

into a sequence of into a sequence of amino acidsamino acids in protein is in protein is

known as translation.known as translation.

translation 2min translation 2min video.asfvideo.asf

Genetic ChangesGenetic Changes

MutationsMutations can be caused by errors in can be caused by errors in

replication, transcription, cell division, or by replication, transcription, cell division, or by

external agents external agents

Mutations in Reproductive CellsMutations in Reproductive Cells

Mutations can affect the reproductive cells ofMutations can affect the reproductive cells of

an organism by changing the an organism by changing the sequencesequence of of

nucleotides within a gene in a nucleotides within a gene in a spermsperm or an or an

eggegg cell. cell.

If this cell takes part in If this cell takes part in fertilizationfertilization. The . The

altered gene would become part of the altered gene would become part of the

genetic makeup of the genetic makeup of the offspringoffspring. .

The mutation may produce a new The mutation may produce a new traittrait or it or it

may result in a protein that does not work may result in a protein that does not work

correctly, resulting in structural or functional correctly, resulting in structural or functional

problems in cells & in organisms. problems in cells & in organisms.

In rare cases, a gene mutation may have In rare cases, a gene mutation may have

positivepositive effects, helping an organism by effects, helping an organism by

making it stronger or faster, better able to making it stronger or faster, better able to

survive in it’s environment.survive in it’s environment.

Mutations in Body CellsMutations in Body Cells

If a cell’s DNA is changed, this mutation If a cell’s DNA is changed, this mutation

wouldwould notnot be passed on to offspring. be passed on to offspring.

However, the mutation may cause However, the mutation may cause

problems for the individual. problems for the individual.

Give 2 examples:Give 2 examples:

1.1. stop stomach acid production needed forstop stomach acid production needed for

digestiondigestion

2. cause skin cells to lose elasticity2. cause skin cells to lose elasticity

Some mutations of DNA in body cells affect Some mutations of DNA in body cells affect

genes that control genes that control cellcell divisiondivision. This can . This can

result in the cells growing and dividing result in the cells growing and dividing

rapidly, producing rapidly, producing cancercancer..

Point mutation is a change in a single base Point mutation is a change in a single base pair in pair in DNADNA. A change in a single amino . A change in a single amino acid can affect the shape of the acid can affect the shape of the proteinprotein..

Frameshift MutationFrameshift Mutation is when a single base is is when a single base is added of deleted from DNA.added of deleted from DNA.

FrameshiftFrameshift mutation is more harmful than mutation is more harmful than pointpoint mutation. mutation.

Chromosomal MutationsChromosomal Mutations

Chromosomal mutations can take place Chromosomal mutations can take place

during either mitosis or meiosis. during either mitosis or meiosis.

They result in They result in structuralstructural changes in changes in

chromosomes.chromosomes.

Causes of mutationsCauses of mutations

Some mutations seem to just happen, Some mutations seem to just happen,

however many mutations are caused by however many mutations are caused by

factors in the factors in the environmentenvironment. Any agent that . Any agent that

can cause a change in DNA is called a can cause a change in DNA is called a

mutagenmutagen. .

Three examples are:Three examples are:

1. radiation1. radiation

2. chemicals2. chemicals

3. high temperatures3. high temperatures