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I bet that you can read this information but not the one above.I bet that you can read this information but not the one above.

-.. -.-- --- ..- .-. …. --- -- . .-- --- .-. -.--.. -.-- --- ..- .-. …. --- -- . .-- --- .-. -.-

There must be at least 2 signalsThere must be at least 2 signals

The order of the signals is importantThe order of the signals is important

The grouping of the signals is importantThe grouping of the signals is important

The requirements for an information The requirements for an information system or a code:system or a code:

DNA Structure and FunctionDNA Structure and Function

Nucleotide:Nucleotide:

SugarSugar

PhosphatePhosphate

Nitrogen BaseNitrogen Base

Nitrogen Bases:Nitrogen Bases:

Purines: Adenine and Purines: Adenine and Guanine Guanine

Pyrimidines: Cytosine and Pyrimidines: Cytosine and ThymineThymine

Functions of DNAFunctions of DNA

• Information to make proteinsInformation to make proteins

• Copy itself (must pass information on to Copy itself (must pass information on to new cellsnew cells

Structure Function RelationshipsStructure Function Relationships

Base Pairs:Base Pairs:

Why do Purines only bond with Pyrimidines?Why do Purines only bond with Pyrimidines?

Why does only A pair with T and G pair with CWhy does only A pair with T and G pair with C

Bonding:Bonding:

Why is the backbone bonded together with covalent bonds?Why is the backbone bonded together with covalent bonds?

Why are the base pairs hydrogen bondedWhy are the base pairs hydrogen bonded

Determination of DNA StructureDetermination of DNA Structure• Rosalind Franklin develops new x-ray Rosalind Franklin develops new x-ray

crystallography technique to get a clear picture crystallography technique to get a clear picture of DNAof DNA

• In 1953 Watson and Crick In 1953 Watson and Crick

published the structure of DNApublished the structure of DNA

using Franklin’s using Franklin’s

data withoutdata without

her knowledgeher knowledge

What the X-ray Crystallography What the X-ray Crystallography Looked LikeLooked Like

DNA is obviously the information molecule – It DNA is obviously the information molecule – It plays both a genetic role and a hereditary roleplays both a genetic role and a hereditary role

• How much information is there in the DNA of a cell?How much information is there in the DNA of a cell?• 6 x 106 x 109 9 base pairs per cellbase pairs per cell• 0.34 nm (100.34 nm (10-9-9m) between base pairsm) between base pairs• The length of DNA/cell The length of DNA/cell = 2 m= 2 m

• Amount of DNA in 1 cell is equal to 30 complete sets of Encylopedia Amount of DNA in 1 cell is equal to 30 complete sets of Encylopedia BrittanicaBrittanica

• If the nucleus was the size of a tennis ball, there would be 4 miles of If the nucleus was the size of a tennis ball, there would be 4 miles of DNA in it.DNA in it.

• How do you fit 2 m of DNA in a 1x10-5 nucleus?How do you fit 2 m of DNA in a 1x10-5 nucleus?Compaction RatioCompaction Ratio– 20m thread/.02m capsule = 20m thread/.02m capsule = – 1000 x compacted1000 x compacted

– 2m DNA/1x10-5 m nucleus = 2m DNA/1x10-5 m nucleus = – 200,000 x compact200,000 x compact

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DNA is arranged into chromatin – wrapped around proteins to pack DNA is arranged into chromatin – wrapped around proteins to pack it init in

There is a lot of DNA in one cell!There is a lot of DNA in one cell!

ChromatinChromatin

• ChromatinChromatin – 2 m of DNA must fit in a 1x10 – 2 m of DNA must fit in a 1x10-5-5 m m nucleus. DNA wrapped around proteins to nucleus. DNA wrapped around proteins to organize it and allow it fit into the nucleusorganize it and allow it fit into the nucleus

• Remember – it is condensed 200,000 x to fit in Remember – it is condensed 200,000 x to fit in the nucleusthe nucleus

• It is still loosely coiled enough that enzymes can It is still loosely coiled enough that enzymes can get into the DNA to copy it and make mRNA for get into the DNA to copy it and make mRNA for protein synthesisprotein synthesis

• It is the normal form of DNA during all phases of It is the normal form of DNA during all phases of the cell cycle except mitosisthe cell cycle except mitosis

ChromatinChromatin

ChromosomesChromosomes

• DNA compacted 12,000 times from DNA compacted 12,000 times from chromatinchromatin

• Cannot read or copy the DNA in Cannot read or copy the DNA in chromosomes – it is too tightly woundchromosomes – it is too tightly wound

• Formed solely during mitosis in order to Formed solely during mitosis in order to divide the doubled DNA in ½ divide the doubled DNA in ½

• Protects the DNA when the nucleus Protects the DNA when the nucleus breaks down in mitosisbreaks down in mitosis

A Real ChromosomeA Real Chromosome

DNA released DNA released from a from a

chromosomechromosome

What is the relationship between DNA,

genes, chromosomes, and the genome? • A gene is a segment of DNA that codes for a protein• There are thousands of genes on each chromosome

– which is a folded up piece of chromatin• All of the genes on all of the chromosomes is the

genome

The Cell Cycle

G0

Hours to days

Making proteins

Normal cell functions

Makes an exact copy of DNA

3-6 hours

Growth 1

Makes a few proteins to get ready for mitosis

Growth 2

2 new cells form

DNA Replication is Semi-DNA Replication is Semi-ConservativeConservative

AA -- TT

GG -- CC

GG -- CC

CC -- GG

AA -- TT

TT -- AA

TT -- AA

CC -- GG

AA

GG

GG

CC

AA

TT

TT

CC

TT

CC

CC

GG

TT

AA

AA

GG

- T- T

- CC

- C- C

- G- G

- T- T

- A- A

- A- A

- G- G

A -A -

G -G -

G -G -

C -C -

A -A -

T -T -

T -T -

C -C -

Replication Problems to OvercomeReplication Problems to Overcome

• If you open all 2 m of DNA it will If you open all 2 m of DNA it will randomly base pair and tangle uprandomly base pair and tangle up

• How do you copy 6x10How do you copy 6x1099 base pairs in 3- base pairs in 3-6 hours6 hours

Steps of ReplicationSteps of Replication• Enzymes open the DNA at Origins of Enzymes open the DNA at Origins of

Replication Replication (there are many on each piece of DNA)(there are many on each piece of DNA)

– Each origin makes 2 replication forksEach origin makes 2 replication forks

• Helicase begins to unzip DNA Helicase begins to unzip DNA • Many DNA polymerase enzymes add Many DNA polymerase enzymes add

the complementary nucleotides the complementary nucleotides (they form (they form

covalent bonds between the sugar of 1 nucleotide and the phosphate covalent bonds between the sugar of 1 nucleotide and the phosphate of another)of another)

• DNA proof-reading enzymes check for DNA proof-reading enzymes check for mistakes (this happens as base pairs mistakes (this happens as base pairs are added)are added)

DNA Mutations – DNA Mutations – change in 1 or more nucleotide change in 1 or more nucleotide

nitrogen bases in the DNAnitrogen bases in the DNA

• Errors in replication – DNA polymerase Errors in replication – DNA polymerase makes an error about 1000 base pairsmakes an error about 1000 base pairs

• DNA proofreading enzymes attached to DNA proofreading enzymes attached to the polymerase correct the mistakesthe polymerase correct the mistakes

• There are usually about 3-6 permanent There are usually about 3-6 permanent mistakes/replicationmistakes/replication

How can mutations occurHow can mutations occur

• A mistake in replication not picked up by A mistake in replication not picked up by the proofreading enzymethe proofreading enzyme

• Environmental insultsEnvironmental insults

Radiation (UV, X-rays, radioactive Radiation (UV, X-rays, radioactive molecules)molecules)

Toxic chemicals in air, food, Toxic chemicals in air, food, cigarette cigarette smokesmoke

How can mutations affect cells and organisms?

• It may not change anything in the cell at all

• If nucleotides change, repair enzymes may fix them

• If nucleotides are changed and repair enzymes don’t fix them, the cell should undergo apoptosis (cell suicide) before it enters S phase.

How can mutations affect cells and organisms?

• If the change isn’t picked up by repair enzymes and the cell doesn’t undergo apoptosis:– It can make a cell make a mishappen protein

– That protein can be a little or a lot mishappen

– Depending on how mishappen and how important that protein is to the cell will determine if the cell malfunctions or not

– If it malfunctions – the cell may die or it could become cancerous

How can mutations affect cells and organisms?

• Unless it becomes cancerous – the malfunctioning cell will not change or affect the organism as a whole!

• In order for a mutation to have an effect on the organism as a whole – it must occur in the sperm, egg, or embryo – then every cell of the offspring’s body will have the mutation so it will actually change the trait of the organism.

Effects of DNA Mutations on Effects of DNA Mutations on Organisms (if in sperm or egg)Organisms (if in sperm or egg)

• No effectNo effectChange is not in a geneChange is not in a geneStill codes for same aaStill codes for same aaaa change doesn’t change protein foldingaa change doesn’t change protein folding

• Negative EffectNegative EffectSignificantly changes protein shape so that Significantly changes protein shape so that

a a function cannot be performed or some function cannot be performed or some body body part is misshapen etc.part is misshapen etc.

• Positive EffectPositive EffectThe change in the protein shape gives the The change in the protein shape gives the organism a survival advantageorganism a survival advantage