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DNA: History, structure, and replication
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Bellwork 10/3/14 1. Correct yesterday’s bellwork: carbon dioxide, light energy is converted into chemical energy. The process of cellular respiration is essential in the oxygen/carbon dioxide cycle. Respiration removes ________ from the atmosphere and produces and releases ________ to the atmosphere. glucose, oxygen oxygen, glucose carbon dioxide, oxygen oxygen, carbon dioxide
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DNA: What is it & why is it important?
DNA is a nucleic acid (stores genetic information). It can determine an organisms’ traits (what it looks like) by determining the structure of an organism’s proteins.
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DNA: What is it & why is it important?
DNA is the recipe for all living things (code of life). It is found in the NUCLEUS in eukaryotic cells & free floating in the CYTOPLASM in prokaryotic cells.
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WHO DISCOVERED DNA? The structure of DNA was discovered through X-ray experiments by Rosalind Franklin which led James Watson and Francis Crick to the discovery of the structure of DNA in 1953 DNA is a DOUBLE HELIX Rosalind Franklin: Great Minds
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Figure 12–7 Structure of DNA
Section 12-1 Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)
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DNA STRUCTURE DNA is a nucleic acid.
Nucleic acids are built up of nucleotides! Nucleotides: Sugar Nitrogenous base Phosphate Sugar in DNA is called deoxyribose
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DEOXYRIBONUCLEIC ACID
DNA is double stranded Backbone (sides of ladder) is made up of phosphates and sugars Image from:
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DNA STRUCTURE The rungs of the ladder are made up of nitrogen bases.
A=Adenine G= Guanine C = Cytosine T= Thymine
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Nitrogen bases =“Steps of ladder”
Purines (2 rings) Phosphate group G C Pyrimidines (1 ring) Deoxyribose sugar T © Pearson Education Inc, publishing as Pearson Prentice Hall. All rights reserved
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A=T C=G CHARGAFF’S RULES Adenine always bonds across with THYMINE
Guanine always bonds across with CYTOSINE Image from:
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DOUBLE HELIX Hydrogen bonds
between nitrogen bases hold the two strands together. Image from:
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Antiparallel=Strands run in opposite directions
DNA IS ANTIPARALLEL Antiparallel=Strands run in opposite directions
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Complete the bases that will be on the other strand of DNA
TAGCTTCC GGACTTAT CTCAGATC
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DNA in EUKARYOTES is packaged into chromosomes
Humans have approximately 3 billion base pairs (1 m long) 60,000 to 100,000 genes
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DNA in EUKARYOTES is packaged into chromosomes
If the diameter of the DNA (2 nanometers) was as wide as a fishing line (0.5 millimeters) it might stretch as far as 21.2 km (or 13.6 miles) in length which would all have to be packed into a nucleus, the equivalent size of 25 cm in diameter. That is some packaging!
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THINK ABOUT IT How could you get this piece of string into the container?
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Chromosomes vs Chromatin
Unwound DNA How DNA looks when the cell is NOT dividing Chromosomes: Tightly packaged DNA Found only when the cell is dividing
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Structure of rna RNA is the other type of nucleic acid
Made of up of many nucleotides Three main differences from DNA: Sugar is ribose Single stranded Replace Thymine with Uracil RNA can leave the nucleus & DNA can not!! *this is really important when we get to protein synthesis
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RNA VS DNA
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How is dna copied? DNA is copied through a process called DNA replication. It takes place in the NUCLEUS of a cell! It occurs in the S phase of the cell cycle.
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How is dna copied? Semiconservative Replication=
the DNA molecule breaks down the middle and each half is the pattern to make a new half!
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DNA REPLICATION STEPS An enzyme called helicase unzips DNA – hydrogen bonds are broken. Now there are two separate strands of DNA!!
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DNA REPLICATION STEPS 2. DNA Polymerase adds matching bases to one side of the DNA strand (A+T, G+C) DNA Polymerase
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DNA REPLICATION STEPS 3. DNA Polymerase checks the new strands to make sure they are matched correctly. 4. Ligase comes in & glues the DNA back together.
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DNA REPLICATION STEPS 5. Two identical strands of DNA now exist!
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DNA Replication: The Cell’s Extreme Team Sport
DNA REPLICATION VIDEO DNA Replication: The Cell’s Extreme Team Sport
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Figure 16.7 A model for DNA replication: the basic concept (Layer 1)
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Figure 16.7 A model for DNA replication: the basic concept (Layer 2)
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Figure 16.7 A model for DNA replication: the basic concept (Layer 3)
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Figure 16.7 A model for DNA replication: the basic concept (Layer 4)
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Replication: http://www. youtube. com/watch
Replication: Real Time:
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DNA Replication Song
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