Chromosomes DNA Replication TSW explain how the genetic

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Chromosomes & DNA Replication TSW explain how the genetic code is contained within DNA

Chromosomes & DNA Replication TSW explain how the genetic code is contained within DNA

DNA & Chromosomes Prokaryotes: single, circular chromosome ¡ Eukaryotes: DNA in nucleus of the

DNA & Chromosomes Prokaryotes: single, circular chromosome ¡ Eukaryotes: DNA in nucleus of the cell in the form of multiple chromosomes ¡

Chromosome # Varies widely between species ¡ Example: ¡ l l l Humans: 46

Chromosome # Varies widely between species ¡ Example: ¡ l l l Humans: 46 Giant Sequoia Tree: 22 Drosophila: 8

DNA Length Extremely long (more than 1 m in the nucleus of a human

DNA Length Extremely long (more than 1 m in the nucleus of a human cell!) ¡ Must be tightly folded to fit inside of the nucleus ¡ Q: How does this work? ¡ A: Chromosomes ¡

Chromosome Structure CHROMATIN: DNA that is tightly coiled around proteins called HISTONES ¡ NUCLEOSOME:

Chromosome Structure CHROMATIN: DNA that is tightly coiled around proteins called HISTONES ¡ NUCLEOSOME: DNA+Histone ¡ l l Pack together to form a thick fiber with loops and coils Allows a lot of DNA to fit in such a small space

Chromatin ¡ Usually dispersed until MITOSIS where the chromatin condenses into individual chromosomes l

Chromatin ¡ Usually dispersed until MITOSIS where the chromatin condenses into individual chromosomes l Do you remember which phase?

DNA Replication Facts ¡ ¡ ¡ DNA has to be copied before a cell

DNA Replication Facts ¡ ¡ ¡ DNA has to be copied before a cell divides DNA is copied during the S or Synthesis Stage of Interphase New cells will need identical DNA strands

DNA Replication Each strand of the DNA double-helix has all the info needed to

DNA Replication Each strand of the DNA double-helix has all the info needed to construct the other half via “base-pairing” ¡ 2 strands are complementary ¡

Duplicating DNA Copying DNA called REPLICATION ¡ Results in 2 DNA molecules that are

Duplicating DNA Copying DNA called REPLICATION ¡ Results in 2 DNA molecules that are identical to each other & the original strand ¡

How does replication occur? Enzymes “unzip” the DNA molecule (DNA Helicase) ¡ “unzipping”: H

How does replication occur? Enzymes “unzip” the DNA molecule (DNA Helicase) ¡ “unzipping”: H bonds break between nucleotides & the 2 strands of DNA unwind ¡

DNA Polymerase Enzyme (-ase) ¡ Joins individual nucleotides ¡ “proofreads” new strand to maximize

DNA Polymerase Enzyme (-ase) ¡ Joins individual nucleotides ¡ “proofreads” new strand to maximize odds that each molecule is a perfect copy ¡

Proofreading New DNA Polymerase initially makes about 1 in 10, 000 base pairing errors

Proofreading New DNA Polymerase initially makes about 1 in 10, 000 base pairing errors ¡ Enzymes proofread and correct these mistakes ¡ The new error rate after proofreading is 1 in 1 BILLION base pairing errors ¡

DNA Damage and Repair Chemicals and ultraviolet radiation damage the DNA in our body

DNA Damage and Repair Chemicals and ultraviolet radiation damage the DNA in our body cells ¡ Cells must continuously repair DAMAGED DNA ¡ Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA ¡ DNA polymerase and DNA ligase replace & bond new nucleotides together ¡

What does replication look like?

What does replication look like?