Structure of DNA & Replication (6a) Identify components of DNA and describe how information for specifying traits of an organism is carried in the DNA. (6b) Recognize that components that make up the genetic code are common to all organisms.

DNA Deoxyribonucleic Acid Where is it found? ALL CELLS HAVE DNA Nucleus of Eukaryotic Cells Cytoplasm of Prokaryotic Cells What does it do? Contains genes that code for traits. Controls cells activities

Structure of DNA Shape of DNA referred to as Double Helix Made up of: Hydrogen Bonds Shape of DNA referred to as Double Helix Made up of: Sugar-Phosphate Backbone Nitrogen bases connected by hydrogen bonds Sugar-Phosphate Backbone Nitrogen Bases

Monomer of DNA - Nucleotide DNA is made of repeating nucleotides: Nucleotides consist of 3 parts: Sugar (Deoxyribose) Phosphate Nitrogen Bases Sugar Deoxyribose phosphate Nitrogen Base 4types

Circle each nucleotide in your diagram. How many nucleotides are shown?

Nitrogen Bases & Pairing Rules In DNA, there are 4 possible nitrogen bases. 1 . 2. 3. 4. Adenine Guanine Cytosine Thymine Adenine and Thymine always pair together Guanine and Cytosine always pair together

Importance of Nitrogen Bases Nitrogen bases = the genetic code Sequence of nitrogenous bases determines the characteristics or traits of an organism. The more similar two organisms are, the more similar their order of nucleotides or nitrogenous bases will be. DNA -> Gene -> Protein -> Trait

DNA Replication Replication = making copies of DNA When a new cell is created (through mitosis), DNA must be created to control the new cell. One original parent DNA molecule is copied to create two identical daughter DNA molecules. Parent DNA Daughter DNA

STEPS OF DNA REPLICATION Double helix unwinds STEP 2: Parent strands separate or “unzip” STEP 3: Parent strands serve as templates for building new strands of DNA STEP 4: End result is 2 identical molecules of DNA

Mitosis & Meiosis (5a) Describe the stages of the cell cycle including DNA replication and mitosis and the importance of the cell cycle to the growth of organisms. (6g) Recognize the significance of meiosis to sexual reproduction.

Somatic Cells (Body cells) Types of Cells Somatic Cells (Body cells) Gametes (Sex cells) All cells other than sex cells Made by mitosis Contain 2 copies of each chromosomes (homologous chromosomes) diploid cells = # 2n Ex. Humans =46 chromosomes Egg and sperm cells Made by meiosis Contain 1 copy of each chromosome Haploid = # 1n Ex. Humans: =23 chromosomes

Steps of Mitosis – for growth and repair Growth & DNA Replication occurs Chromosomes condense Chromosomes line up in middle of cell Chromosomes pull apart (And Cytokinesis) Cell and chromosomes divide into two separate cells

Disadvantages of Mitosis Mitosis produces specialized cells (ex. Liver, heart, and nerve cells) Controlled by gene regulation – genes turned on and off in different cells to produce different shapes, structures, and functions. Cancer – unregulated growth of cells leading to tumors in the body. Disadvantages of Mitosis

Steps of Meiosis – to produce sex cells

Meiosis – 2 Rounds of Division Interphase I: DNA Replication Prophase I: Chromosomes form TETRAD, crossing-over occurs Metaphase I: Tetrads line up in middle Anaphase I: Tetrads pull apart Telophase I: 2 daughter cells produced ****NO DNA REPLICATION***** Prophase II: 2 daughter cells prepare to divide Metaphase II: chromosomes line up Anaphase II: chromosomes split Telophase & Cytokinesis: 4 genetically different daughter cells produced

Advantages of Sexual Reproduction Produces GENETIC VARIATION Offspring genetically different from each other and parents – may provide better chances of survival! Mutations can arise in sex cells – leading to gene or chromosomal mutations. Ex. Down’s syndrome (trisomy 21) Disadvantages of Sexual Reproduction

Comparison of Mitosis & Meiosis Produces somatic cells For growth and repair 1 round of division 2 genetically identical cells produced Can lead to cancer Meiosis: Produces gametes For sexual reproduction 2 rounds of division 4 genetically different cells produced Can lead to genetic abnormalities