Deoxyribonucleic Acid & Cell Reproduction

1. Deoxyribonucleic Acid & Cell Reproduction Chapter 10-1, Chapter 8 (pg 184-189; pg 144 - 156)

2. Unit 6: lecture 1 • Topics: • DNA Structure • Covers information from: • Chapter 10-1 (pgs 185 – 187)

3. WHAT IS DNA? • DNA- Deoxyribonucleic Acid • EVERY living organism has its own unique DNA • DNA stores all genetic (hereditary) information • DNA is known as the “blueprint” for an organism, it tells the body what it will look like • Each gene codes for a different trait or appearance • Each gene is a code for a protein • Each strand of DNA (chromosome) contains hundreds of genes!

4. WHAT IS DNA? • Structure • DNA structure was discovered in 1953 by James Watson and Francis Crick • Took X-ray pictures of DNA molecule • Used photography technique developed by another scientist, Rosalind Franklin • The shape of DNA was described as a “double helix” • Each DNA molecule is made up of two long strands of molecules known as NUCLEOTIDES • There are four types of nucleotides in DNA • T = Thymine  A = Adenine • C = Cytosine G = Guanine

5. WHAT IS DNA? • Each DNA nucleotide is made up of three parts: • A sugar molecule (DEOXYRIBOSE) • A phosphate group • A nitrogen containing base

6. WHAT IS DNA? • The sugar and phosphate are identical in each DNA nucleotide • The shape and structure of the nitrogen base is what makes each nucleotide different • Thymine and Cytosine have a single ring structure • PYRIMIDINE– single ring nitrogen base • Adenine and Guanine have a double ring structure • PURINE– double ringed nitrogen base

7. WHAT IS DNA? • To connect the two strands, two nucleotides attach, or pair, together • Adenine always pairs with Thymine • A pairs with T • Guanine always pairs with Cytosine • G pairs with C • Purines can only pair with pyrimidines because of the shape of the nitrogen base • When two DNA nucleotides pair together, they are called COMPLEMENTARY BASE PAIRS • Held together by hydrogen bonds

8. WHAT DOES a molecule of DNA LOOK LIKE? • Each DNA molecule is made up of two long strands of nucleotides • The two strands are parallel & are connected by the pairing of the complementary base pairs • The shape of DNA is described as a “double helix” or a twisted ladder • Parts of a DNA molecule • Phosphate & Sugar backbone • B. Nitrogen base • (center of helix, "rungs” of the ladder) • The nitrogen bases from the 2 strands are attached by Hydrogen bonds

9. End of lecture 1

10. Unit 6: lecture 2 • Topics: • DNA Replication • Mutations • Covers information from: • Chapter 10-1 (pgs 188 – 189)

11. CELL DIVISION • Remember The Cell Theory: • All cells come from the division of pre-existing cells. • CELL DIVISION - process where a cell splits to produce a new cell • Before a cell divides, all the genetic material (DNA) must be copied. • This will allow for both cells (2 after cell splits) to have a complete copy of the genetic material.

12. HOW DOES DNA REPLICATE? • DNA REPLICATION- when a strand of DNA copies itself • The two parallel strands are pulled apart. The bonded complementary base pairs separate. • Two sides of DNA are separated by enzymes called HELICASES • Helicase enzyme moves along DNA, breaking hydrogen bonds between base pairs (separates left & right strands)

13. HOW DOES DNA REPLICATE? • DNA POLYMERASE (another enzyme) bonds to each separated strand and makes a new complementary strand of DNA for each side. • New hydrogen bonds form between base pairs • 5. Two new exact copies of the original DNA molecule are produced • Each new DNA molecule has • 1 old strand and • 1 newly copied strand

15. CAN THE ENZYMES MAKE MISTAKES? • YES! Known as a MUTATION • Mutations can be caused if: • The order of nucleotides changes, wrong nucleotides paired together, or certain sections of DNA were deleted or repeated • Our cells have a proofreading and repair process to fix mutations. Most of the mutations are fixed, but some are overlooked. • About 1 in every 1 billion nucleotides is a mutation • If a mutation changes the order of nucleotides in a gene, which can change the appearance of that trait. • Mutations can happen: • When DNA is making a copy of itself. • When a gene in DNA is being used to make a protein • If you are exposed to harmful chemicals and/or UV rays

16. CAN THE ENZYMES MAKE MISTAKES? • Mutations can have the following affect on the organism: • Negative – some mutations are very bad and can even be fatal • Positive – some mutations can actually be helpful • Neutral – some mutations don’t affect the organism at all • Some of the most common types of mutations are: • Substitutionis when one nucleotide is changed to another; • Example: Car Cat • Additionis when one nucleotide is added in the sequence • Example: Car Care • Deletionis when one or more nucleotides are removed from the sequence; • Example1: Car  Cr; Example 2: Automobile  Auto

17. End of lecture 2

18. Unit 6: Lecture 3 • Topics: • Introduction to Cell Division • Binary Fission • Cell Cycle – Interphase • Covers information from: • Chapter 8-2 (pgs 148 – 149)

19. How do cells divide? • Cell division is just one small part of the cell cycle • For the majority of the cell’s life, it is doing normal cellular activities. • Cell division makes up about 10% - 20% of the cell cycle • Prokaryotic Cell Division – Binary Fission • Eukaryotic Cell Division – Mitosisor Meiosis • Mitosis • How unicellular organisms replicate (asexual reproduction) • How multicellular organisms add more cells to their body • Meiosis • Produces reproductive cells

20. How do cells divide? • Binary Fission • Prokaryotic cell division • Remember:Prokaryotic cells do not have a nucleus or membrane bound organelles ex: bacteria • 3 Step Process: • DNA is copied • Cell grows to two times its original size • Cell splits in two • This process happens very quickly • Type of asexual reproduction • Produces two identical organisms, No genetic diversity

21. Binary Fission E. coli going through binary fission

22. How do cells divide? • EUKARYOTIC CELL DIVISION • Remember: Eukaryotic cells have a nucleus and membrane-bound organelles; ex: animal, plant, fungus, protist • Eukaryotic cell division is more complicated and a more involved process than prokaryotic cell division • Eukaryotic Cell Cycle - 2 PARTS • 1. INTERPHASE • Makes up 80% - 90% of a cell’s life, Time between cell division • Cell is doing normal cellular activities and preparing to divide • Stages in Interphase: G1 , S PHASE, G2 •  2. DIVISION: M PHASE (Mitosis or Meiosis), CYTOKINESIS • * After cytokinesis, the cells begin G1 again

23. Cell Cycle (pg 149)

24. How do cells divide? • INTERPHASE • 1. G1 PHASE - GAP 1 • First time gap, cell grows to mature size, does normal cellular activities • 2. S PHASE – DNA SYNTHESIS • DNA replicates • 3. G2 PHASE - GAP 2 • Second time gap, cell grows and gets ready to divide • If the cell is not ready to continue, it wont pass these steps • It will take a break and go into a phase of the cycle known as G0 • A cell can stay in G0 for days, months, even years!

25. How do cells divide? • DIVISION • 1. “M PHASE” (MITOSIS or MEIOSIS) • Has 4 steps: Prophase, Metaphase, Anaphase, Telophase •  2. CYTOKINESIS

26. End of lecture 3

27. Unit 6: Lecture 4 • Topics: • Cell Division • Mitosis • Meiosis • Covers information from: • Chapter 8-1 (pgs 145 – 146) • Chapter 8-2 (pgs 150 – 151) • Chapter 8-3 (pgs 153 – 156)

28. Unit 6: Lecture 4 • DIVISION • 1. “M PHASE” (MITOSIS or MEIOSIS) • Mitosis – Division of the nucleus • Has 4 steps: Prophase, Metaphase, Anaphase, Telophase •  2. CYTOKINESIS • Cytokinesis – Division of the cytoplasm

29. STAGES OF division

30. STAGES OF division (m phase) • A. PROPHASE • DNA wraps around Histones to become more condensed and organized, now known as a Chromosome • HISTONE– structural protein • CHROMOSOME– condensed, organized strand of DNA • Remember: DNA just replicated, so there are 2 copies of every strand of DNA • The identical copies are held together by a CENTROMERE • Each half is called a CHROMATID • Both halves together are called SISTER CHROMATIDS and looks like an “X” • Nucleolus and nuclear membrane (envelope) break down • Two CENTROSOMES appear and move to opposite ends of the cell • Centrosomes separate and begin to make specialized microtubules known as SPINDLE FIBERS

33. STAGES OF division (m phase) • B. METAPHASE • Chromosomes (Sister Chromatids) line up in the middle of the cell • Spindle fibers attach to each side of the centromere on the sister chromatids • C. ANAPAHSE • Spindle fibers shorten and break the centromere in half  • Sister chromatids separated and each half is pulled to an opposite end of the cell • D. TELOPHASE • Spindle fibers break down • Nuclear membrane (envelope) reforms around both groups of chromosomes • Cell gets ready to split

34. STAGES OF division • 2. CYTOKINESIS • CYTOKINESIS- dividing of the cytoplasm • Steps: • Cell membrane pinches inward • Cytoplasm divides • Cell pinches into 2 cells • Two identical cells are formed • In humans, produce body cells (SOMATIC CELLS) • Each somatic cell has 46 chromosomes • *PLANTS - cell wall can't pinch in, so plants form a CELL PLATE • New cell wall forms in the middle of the cell

36. Meiosis Produces GAMETES Gamete – Reproductive cell, aka Haploid Cell divides twice Results in 4 new cells In humans, each gamete has 23 chromosomes Meiosis I - 1st division Meiosis II - 2nd division Separates sister chromatids

37. FORMATION OF GAMETES • Males produce four gametes of equal size • Known as SPERMATOGENESIS • Females produce one large gamete, and three non-functional gametes (Polar Bodies) • Divides cytoplasm unequally • Known as OOGENESIS

39. End of lecture 4