DNA Structure and Analysis

Central Idea of Genetics!

DNA RNA PROTEINTranscription Translation

There are four kinds of bases in DNA:

• adenine• guanine • cytosine• thymine

DNA Structure

• Nucleotides join together to form long strands• DNA consists of two strands• Strands twist around each other to form a double helix• Nucleotides are held together by a phosphodiester bond

– Connects the sugar of one nucleotide to the phosphate of another

• Nucleotide sequence can vary

Phosphodiester bonds

DNA Structure

• DNA consists of two strands joined together by hydrogen bonds between the base pair

• Base pairs are complementary on opposite strands– Adenine only base pairs with thymine– Guanine only base pairs with cytosine

• Two strands are considered antiparallel because the polarity of each strand opposite– Necessary for nitrogen bases to align and form

hydrogen bonds

DNA Structure

DNA Double Helix

Polarity of DNA

• Each strand of nucleotides has a 5’ end and 3’ end– The 3’ end used to bond to another nucleotide– The 5’ end is attached to the phosphate group

of the nucleotide

• A strand of DNA runs from the 5’ 3’

•Each carbon in the deoxyribose is numbered 1’-5’

DNA structurehttp://academic.brooklyn.cuny.edu/biology/bio4fv/page/molecular%20biology/dna-structure.html

DNA Animations

• http://www.pbs.org/wgbh/nova/genome/dna.html# • http://learn.genetics.utah.edu/content/begin/tour/• http://www.johnkyrk.com/DNAanatomy.html• http://www.sumanasinc.com/webcontent/animations/conten

t/DNA_structure.html

Chromosomes and DNA Replication

DNA makes up chromosomes!

DNA and Chromosomes

• In prokaryotic cells, DNA is located in the cytoplasm.• Most prokaryotes have a single DNA molecule

containing nearly all of the cell’s genetic information.

DNA and Chromosomes

• Many eukaryotes have 1000 times the amount of DNA as prokaryotes.

• Eukaryotic DNA is located in the cell nucleus inside chromosomes.

• The number of chromosomes varies widely from one species to the next.

DNA and Chromosomes• Chromosome Structure

– Eukaryotic chromosomes contain DNA and protein, tightly packed together to form chromatin.

– Chromatin consists of DNA tightly coiled around proteins called histones.

– DNA and histone molecules form nucleosomes. – Nucleosomes pack together, forming a thick fiber.

DNA Replication

• Necessary to create new cells!• Each strand of DNA has all the

information needed to reconstruct the other half

• Strands are complementary and can be used to make the other strand

• Semiconservative Replication– Parent strands

separate and serve as templates for new strands

– New DNA molecule holds one parent strand and one new strand

DNA Replication

DNA Replication

1. The DNA molecule separates into two strands.2. Produces two new complementary strands

following the rules of base pairing.3. Each strand of the double helix of DNA serves as a

template for the new strand.

DNA Replication

Nitrogen Bases

Replication Fork

DNA Polymerase

Replication Fork

Original strandNew Strand

Growth

Growth

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• http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf

• http://www.youtube.com/watch?v=hfZ8o9D1tus• http://www.youtube.com/watch?v=4jtmOZaIvS0

DNA Replication

1. Unwinding - Enzymes unzips DNA by breaking hydrogen bonds. Strands separate at the replication fork.

Replication Fork

DNA Replication

2. Base Pairing - New complementary nucleotides are added to the 3’ end to make a new strand – the new strands are formed in opposite directions; the enzyme DNA polymerase attaches nucleotides to produce new strands.

DNA Replication

3. Joining- DNA polymerase joins the fragments together. The new DNA strand is proofread

DNA Replication

RNA and Protein Synthesis

Genes are coded DNA instructions that control the production of PROTEINS.

Genetic messages can be decoded by copying part of the nucleotide sequence from DNA

into RNA.

RNA contains coded information for making proteins.

Central Idea of Genetics!

DNA RNA PROTEINTranscription Translation

RNA

RNA – Ribonucleic Acid– Composed of a long strain of nucleotides– Contains sugar, phosphate group, and nitrogen base

RNA DNA

Ribose sugar Deoxyribose sugar

Singe-stranded Doubled-stranded

Uricil Thymine

RNATypes:

– Messenger RNA (mRNA) – messenger from DNA to the rest of the cell

– Ribosomal RNA (rRNA) – make up ribosomes

– Transfer RNA (tRNA) – transfer amino acids to the ribosomes

Transcription

• The process of making RNA by copying part of the DNA sequence into a complementary RNA sequence

Transcription

Requires enzyme RNA polymerase

1. RNA Polymerase binds to DNA and separates strands

2. RNA Polymerase uses DNA as template and assembles complementary RNA strands

Transcription

Transcription Animations• http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf

RNA Editing

• The DNA of eukaryotic genes contains sequences of nucleotides, called introns, that are not involved in coding for proteins.

• The DNA sequences that code for proteins are called exons.

• When RNA molecules are formed, introns and exons are copied from DNA.

RNA Editing

• The introns are cut out of RNA molecules.

• The exons are the spliced together to form mRNA.

Protein Review

• Proteins are made by joining – AMINO ACIDS

• Each protein contains a combination of the 20 amino acids

• The function of the protein is determined by number and sequence of amino acids

• (A polypeptide is a protein!)Protein 1

Protein 2

Genetic Code• The genetic code is the “language” of mRNA instructions.• A codon consists of three consecutive nucleotides on

mRNA that specify a particular amino acid.

Each codon specifies a particular amino acid that is to be placed on the polypeptide chain.

Genetic Code

RNA Sequence -

U C G C A C G G U

Codon Sequence – U C G – C A C – G G U

Use the Amino Acid Guide to determine amino acid –

U C G – C A C – G G U

Amino acid sequence –

U C G – C A C – G G U

Serine – Histidine – Glycine

Translation

• Translation is the decoding of an mRNA message into a polypeptide chain (protein).

• Translation takes place on ribosomes.

• During translation, the cell uses information from messenger RNA to produce proteins.

Translation

1. Messenger RNA is transcribed in the nucleus, and then enters the cytoplasm where it attaches to a ribosome.

Translation2. The ribosome “reads” the mRNA codon and

the corresponding amino acid is brought to the ribosome by the tRNA

codon

Amino Acid

Amino Acid

Translation3. The ribosome forms bonds between the

amino acids to form the proteinBond formed

Translation 4. Translation

continues until the ribosome reaches a stop codon on the mRNA and releases the protein (polypeptide)

The BIG Picture!

Translation Animation

• http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a3.html

• http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf