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Question: Why don’t we all look alike?

Explore the fascinating world of DNA and discover why all living things look different. Learn about the structure of DNA, how it replicates, and the role it plays in determining our traits.

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Question: Why don’t we all look alike?

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  1. DNA – The Code for Life Question: Why don’t we all look alike?

  2. All Living Things… • Have cells. • All cells contain the genetic instructions that make an organism unique.  Adapted to environment, appearance, preferences, behaviors, survival instincts, etc.

  3. DNA • We get our genetic codes/instructions from DNA that is located inside every cell.

  4. Jurassic Park DNA Scene • (Youtube.com)

  5. DNA DNA stands for – Deoxyribonucleic acid Functions of DNA: 1. Carries the codes to make proteins. • Carries the genetic material that is passed on from the parents to the offspring.

  6. Discovery of DNA Invented X-ray diffraction photography. Photo used to determine the shape of DNA is spiral. Rosalind Franklin -

  7. DISCOVERY OF DNA James Watson and Francis Crick used the information from Franklin and other scientists to build a 3-D model of DNA. Won the Nobel Peace Prize in Chemistry in 1961.

  8. Structure of DNA Shape of DNA - Like a twisted rope ladder. This shape is called Double Helix. A single spiral would be called Helix.

  9. STRUCTURE OF DNA Side Pieces (The Rope Part) Are alternating units of a (1) five-carbon sugar and a (2) phosphate group. These go down both sides of the molecule phosphate Sugar (called deoxyribose)

  10. STRUCTURE OF DNA Nitrogen Bases (Steps of the ladder) - • Adenine – A • Thymine – T • Cytosine – C • Guanine - G The bases are connected to the sugar only !!!!!

  11. STRUCTURE OF DNA The nitrogen bases fit together in this way: Adenine always goes with Thymine Cytosine always goes with Guanine The bases are held together by a weak hydrogen bond. Two (2)bonds between A and T, three (3)bonds between C and G.

  12. Purines and Pyrimidines Purines: A & G Pyrimidines: T & C Both basically serve the same purpose but structure is different. Structure allows these to be used in different ways in cells Purines- 2 carbon-nitrogen rings, 4 nitrogen atoms Pyrimidines-1 carbon-nitrogen ring, 2 nitrogen atoms

  13. STRUCTURE OF DNA These three parts form the basic unit of DNA called the NUCLEOTIDE. (subunits of DNA) phosphate Nitrogen base Can be A, T, C or G Sugar (deoxyribose)

  14. STRUCTURE OF DNA The nitrogen bases fit together in this way: Adenine always goes with Thymine Cytosine always goes with Guanine The bases are held together by a weak hydrogen bond. Two (2)bonds between A and T, three (3)bonds between C and G.

  15. phosphate adenine sugar thymine cytocine guanine

  16. STRUCTURE OF DNA One complete turn of the double helix is 10 base pairs or 10 steps on the ladder

  17. DNA Nucleotide Drawing

  18. Where is DNA located? • DNA molecules are coiled up inside of EVERY SINGLE CELL! • The structures that DNA is coiled into are called CHROMOSOMES.  This is how the DNA molecules actually fit inside of tiny cells.

  19. Chromosomes • Definition: The structure that DNA is organized in. • They come in pairs, half from each parent.

  20. NUMBERS OF CHROMOSOMES VS COMPLEXITY The number of chromosomes in the cells of eukaryotes differs from one kind of organism to another and has NOTHING to do with the complexity of the organism. FOR EXAMPLE: Goldfish - 98 Wheat - 42 Human - 46 Potato - 48 Fruit fly - 8 A fern called Ophioglossum reticulatumhas 1,260 chromosomes per cell, more than any other known organism.

  21. CHROMOSOME ARRANGEMENT All regular body cells have all the same parts in multi-cellular organisms and the same # of chromosomes. There are 46 chromosomes in human body cells. Chromosomes always come in pairs. In humans there are 46 chromosomes for a total of 23 pairs. 22 of the pairs are similar. The 23rd pair is different. These are the sex chromosomes. Male xy Female xx

  22. CHROMOSOME ARRANGEMENT HUMAN BODY CELLS HAVE 46 CHROMOSOMES OR 23 PAIRS. Bone cell Nerve cell BULLFROG BODY CELLS HAVE 26 CHROMOSOMES OR 13 PAIR. FRUIT FLY BODY CELLS HAVE 8 CHROMOSOMES OR 4 PAIR.

  23. Gene: segment of DNA on your chromosomes that determines your traits.

  24. Traits • Characteristics about an organism that are determined by the information carried on genes (segments of DNA).

  25. Siblings??? • If you have a sibling, and you both get the DNA from your (same) mom & dad, why don’t you look exactly alike?????

  26. Siblings • Since sex cells only get half the number of chromosomes, each sex cell does not get the same exact half. • During sex cell formation, chromosomes randomly reconnect to form a new gene variety. • (We will talk about this more in reproduction… next unit…)

  27. How does DNA copy itself? Purpose:DNA copies itself to ensure that each new cell that is produced gets the correct number of chromosomes and receives an EXACT copy of the DNA molecule. This is called DNA REPLICATION. The DNA molecule serves as its own pattern or template so as an exact copy can be made.

  28. Replication #1 Replication #2

  29. STEPS OF DNA REPLICATION 1. DNA untwists and unzips down the hydrogen bonds. This is why the bonds had to be WEAK. 2. New nucleotides fill in the naked ends produced by the unzipping process. 3. Nucleotides continue to fill in until the entire strand is complete. 4. This results in 2 new identical DNA molecules.

  30. What happens when there is a problem during replication? • A permanent change in the sequence of DNA is known as a mutation • (a small change that occurs during replication but is caught/corrected is known as a point mutation)

  31. DNA REPLICATION What if there is a mistake? There is always a chance that the wrong nucleotide bonds to another. HOWEVER, DNA has a special enzyme that is responsible for “reading” the bases and recognizing and replacing damaged or wrong nucleotides. This PROOFREADING allows for only one (1) error in ONE BILLION nucleotides.

  32. Possible causes of mutations • Error during replication • Error during fertilization (reproduction) • Outside factors such as X-rays and chemical have ben known to change or breakdown chromosomes

  33. Common mutations (in humans) • Pimples/acne, high fertility (twins), heart disease, diabetes, stroke, high blood pressure, color blindness, heterochromia (two different colors in one eye OR two different colored eyes), red hair, down syndrome, blue eyes, freckles

  34. Different types of mutations

  35. Different types of mutations: Substitution/Inversion • Switches a section of base pairs • Switching an A or a G

  36. Different types of mutations: Insertion and Deletion • Insertion= extra base pairs are inserted into a new plane • Deletion= a section of DNA is lost or deleted

  37. Different types of mutations: Duplication • A piece of DNA is abnormally copied one or more times

  38. Different types of mutations: Translocation • Altered chromosome arrangement

  39. We have been told that DNA is the blueprint for life, BUT what does that mean? DNA holds the instructions that tell a cell how to construct amino acid chains. SO WHAT? Proteins build cells That is important because amino acid chains build proteins. AND

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