DNA: History, structure, and replication

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

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.

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.

WHO DISCOVERED DNA? http:/www.time.com/time/time100/scientist/profile/watsoncrick.html 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

Figure 12–7 Structure of DNA Section 12-1 Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

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

DEOXYRIBONUCLEIC ACID DNA is double stranded Backbone (sides of ladder) is made up of phosphates and sugars Image from: http://www.tokyo-med.ac.jp/genet/picts/dna.jpg

DNA STRUCTURE The rungs of the ladder are made up of nitrogen bases. A=Adenine G= Guanine C = Cytosine T= Thymine

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

A=T C=G CHARGAFF’S RULES Adenine always bonds across with THYMINE Guanine always bonds across with CYTOSINE Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif

DOUBLE HELIX Hydrogen bonds between nitrogen bases hold the two strands together. Image from: http://evolution.berkeley.edu/evosite/evo101/images/dna_bases.gif

Antiparallel=Strands run in opposite directions DNA IS ANTIPARALLEL Antiparallel=Strands run in opposite directions

Complete the bases that will be on the other strand of DNA TAGCTTCC GGACTTAT CTCAGATC

DNA in EUKARYOTES is packaged into chromosomes Humans have approximately 3 billion base pairs (1 m long) 60,000 to 100,000 genes

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!

THINK ABOUT IT How could you get this piece of string into the container? http://www.artzooks.com/files/3966/AZ533823_320.jpg http://www.mivaroo.com/sites/toyconnection.com/

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

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 

RNA VS DNA

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.

How is dna copied? Semiconservative Replication= the DNA molecule breaks down the middle and each half is the pattern to make a new half!

DNA REPLICATION STEPS An enzyme called helicase unzips DNA – hydrogen bonds are broken. Now there are two separate strands of DNA!!

DNA REPLICATION STEPS 2. DNA Polymerase adds matching bases to one side of the DNA strand (A+T, G+C) DNA Polymerase

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.

DNA REPLICATION STEPS 5. Two identical strands of DNA now exist!

DNA Replication: The Cell’s Extreme Team Sport DNA REPLICATION VIDEO DNA Replication: The Cell’s Extreme Team Sport

Figure 16.7 A model for DNA replication: the basic concept (Layer 1)

Figure 16.7 A model for DNA replication: the basic concept (Layer 2)

Figure 16.7 A model for DNA replication: the basic concept (Layer 3)

Figure 16.7 A model for DNA replication: the basic concept (Layer 4)

Replication: http://www. youtube. com/watch Replication: http://www.youtube.com/watch?v=zdDkiRw1PdU Real Time: http://www.youtube.com/watch?v=bee6PWUgPo8

DNA Replication Song https://www.youtube.com/watch?v=b9YvRq4gSg8