DNADNA

DNA-Deoxyribonucleic Acid- DNA-Deoxyribonucleic Acid- molecule that contains molecule that contains genetic information. genetic information.

Genes are segments of Genes are segments of DNA. Chromosomes are DNA. Chromosomes are strands of DNA.strands of DNA.

In the 1950’s it was In the 1950’s it was understood that DNA was understood that DNA was the molecule that stored the molecule that stored genetic information but the genetic information but the structure was unknown.structure was unknown.

DNADNA

Structure of DNAStructure of DNA

James Watson and Francis Crick James Watson and Francis Crick discovered the structure of DNA.discovered the structure of DNA.

Double Helix structure.Double Helix structure. DNA and RNA are classified as nucleic DNA and RNA are classified as nucleic

acids.acids. Each strand of DNA is made of nucleotides- Each strand of DNA is made of nucleotides-

subunits of a nucleic acid. subunits of a nucleic acid. Each nucleotide is made of a phosphate Each nucleotide is made of a phosphate

group, a five carbon sugar (deoxyribose), group, a five carbon sugar (deoxyribose), and a nitrogen-containing base. and a nitrogen-containing base.

Structure of DNAStructure of DNA

There will be the There will be the same number of same number of sugars, phosphates, sugars, phosphates, and bases. and bases.

Sugar-phosphate and Sugar-phosphate and sugar-bases are held sugar-bases are held by strong covalent by strong covalent bonds. bonds.

Base pairs are held Base pairs are held by weak hydrogen by weak hydrogen bonds. bonds.

Pairing between basesPairing between bases

Erwin Chargaff noticed that the amount of Erwin Chargaff noticed that the amount of A=T and the amount of G=C.A=T and the amount of G=C.

In DNA Adenine is always paired with In DNA Adenine is always paired with Thymine and Guanine is always paired Thymine and Guanine is always paired with Cytosine. with Cytosine.

One purine (two rings, A and G) is always One purine (two rings, A and G) is always paired with one pyrimidine (one ring-T and paired with one pyrimidine (one ring-T and C). C).

Pairing between BasesPairing between Bases A - T, and G - C are A - T, and G - C are

complimentary base complimentary base pairs pairs

What is the significance?What is the significance? The sequence on one The sequence on one

strand will determine the strand will determine the sequence on the other sequence on the other strand.strand.

DNA ReplicationDNA Replication"...It has not escaped our notice that the "...It has not escaped our notice that the

specific pairing we have postulated specific pairing we have postulated immediately suggests a possible copying immediately suggests a possible copying mechanism for the genetic material.” mechanism for the genetic material.”

-Watson, J.D., and Crick, F.H.C. 1953."Molecular -Watson, J.D., and Crick, F.H.C. 1953."Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid" Nucleic Acid" NatureNature, April 25, 1953. vol. 171:737-738., April 25, 1953. vol. 171:737-738.

DNA ReplicationDNA Replication

DNA replication is the copying of DNA DNA replication is the copying of DNA before cell division. before cell division.

DNA Replication takes place in the S DNA Replication takes place in the S phase of the cell cycle before Mitosis and phase of the cell cycle before Mitosis and MeiosisMeiosis

Jobs:Jobs: DNA is split.DNA is split. Hold DNA apart.Hold DNA apart. Make new nucleotides.Make new nucleotides. Check for errors. Check for errors.

DNA ReplicationDNA Replication DNA is split by an enzyme known as DNA DNA is split by an enzyme known as DNA

helicase. helicase. DNA is held apart by proteins at the replication DNA is held apart by proteins at the replication

fork.fork. The enzyme DNA polymerase moves along The enzyme DNA polymerase moves along

each strands, and adds the complimentary each strands, and adds the complimentary nucleotides until two new identical copies are nucleotides until two new identical copies are produced. (semi-conservative) produced. (semi-conservative)

DNA polymerase can backtrack to correct DNA polymerase can backtrack to correct incorrect nucleotide base pairings.incorrect nucleotide base pairings.

http://www.maxanim.com/genetics/Dna%20Rephttp://www.maxanim.com/genetics/Dna%20Replication/Dna%20Replication.lication/Dna%20Replication.htmhtm

MeiosisMeiosis

Meiosis is a form of cell division that Meiosis is a form of cell division that produces gametes.produces gametes.

Homologous chromosomes are pairs that Homologous chromosomes are pairs that are similar is size, shape, and genetic are similar is size, shape, and genetic information. information.

Before meiosis begins DNA is replicated. Before meiosis begins DNA is replicated. Chromosomes are replicated and exist Chromosomes are replicated and exist

as two identically attached chromatids. as two identically attached chromatids.

Stages of Meiosis IStages of Meiosis I

Prophase I- Nuclear envelope breaks down, Prophase I- Nuclear envelope breaks down, Homologous chromosomes pair, spindles form.Homologous chromosomes pair, spindles form.

Metaphase I- Homologous chromosomes are Metaphase I- Homologous chromosomes are moved to the equator. moved to the equator.

Anaphase I- Spindle fibers separate the pairs of Anaphase I- Spindle fibers separate the pairs of chromosomes, chromosomes are not split chromosomes, chromosomes are not split along the centromere. along the centromere.

Telophase I- chromosomes move to the poles, Telophase I- chromosomes move to the poles, new nuclear membrane is formed, cytoplasm is new nuclear membrane is formed, cytoplasm is divided. divided.

Stages of MeiosisStages of Meiosis

Prophase II- new spindle forms, nuclear Prophase II- new spindle forms, nuclear membrane breaks down. membrane breaks down.

Metaphase II- The chromosomes line up along the Metaphase II- The chromosomes line up along the equator, attached at the centromere.equator, attached at the centromere.

Anaphase II- each individual chromatid is pulled Anaphase II- each individual chromatid is pulled apart at the centromereapart at the centromere

Telophase II- nuclear envelopes forms, spindle Telophase II- nuclear envelopes forms, spindle breaks down, cytoplasm splits, four haploid cellsbreaks down, cytoplasm splits, four haploid cells

MeiosisMeiosis

Crossing over is the when a piece of a Crossing over is the when a piece of a chromatid on one homologous chromatid on one homologous chromosome is broken and exchanged chromosome is broken and exchanged with another, occurs in prophase I.with another, occurs in prophase I.

Spermatogenesis is meiosis in male testes Spermatogenesis is meiosis in male testes that produce 4 sperm. that produce 4 sperm.

Oogenesis is meiosis in female ovaries Oogenesis is meiosis in female ovaries that produces 1 egg and 3 polar bodies. that produces 1 egg and 3 polar bodies.