Dna structure and replication
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DNA: Structure and Replication. Two Types of Nucleic Acids. Slide # 2. Nucleic Acids : carry the genetic instructions for all life. Discovery of Nucleic Acid. Slide # 3. 1869: Friedrich Miescher discovered nuclein Noticed that nuclein had a lot of phosphate

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DNA: Structure and Replication

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Dna structure and replication

DNA: Structure and Replication

Two types of nucleic acids

Two Types of Nucleic Acids

Slide # 2

Nucleic Acids: carry the genetic instructions for all life

Discovery of nucleic acid

Discovery of Nucleic Acid

Slide # 3

  • 1869: Friedrich Miescher discovered nuclein

    • Noticed that nuclein had a lot of phosphate

  • He found nuclein in every type of cell he studied.

Miescher’s lab

Griffith s experiment

Griffith’s Experiment

Slide # 4

  • 1. 1928: Frederick Griffith

  • a. Showed that bacteria could be transformed

  • b. transformation: process in which bacteria can take up the genes of another bacteria and express those genes

Avery s experiment

Avery’s Experiment

Slide # 5

Oswald Avery continued Griffith’s experiment!

Avery showed that DNA is the transforming agent!

Hershey and chase experiment

Hershey and Chase Experiment

Slide # 6

  • 1. 1952: Hershey & Chase used radioactive markers on viruses

  • a. showed that virus only injects nucleic acid into bacteria

  • b. bacteria take up nucleic acid and can express the new genes

  • c. demonstrated that DNA is the genetic material of the cell

Components of dna

Components of DNA

Slide # 7

DNA is made up small, repeating units (monomers) called nucleotides.

  • Nucleotide has 3 parts:

  • 1. A phosphate group

  • 2. A sugar (called deoxyribose)

  • 3. Nitrogen base (4 different bases)

    • Adenine “A”

    • Thymine “T”

    • Cytosine “C”

    • Guanine “G”





Phosphate group


Go to Section:

Chargaff discovered ratios of nitrogen bases

Chargaff: Discovered Ratios of Nitrogen Bases

Slide # 8

  • 1940’s: Erwin Chargaff discovered that the % of base “A” was almost equal to the % of base “T” & the percent of base “C” was nearly equal to the % of base “G”– didn’t know why

  • Also discovered that composition of DNA (% of A, T, C, & G) varies from species to species

  • Both discoveries gave support that DNA carries the genetic code!


Percentage of bases in four organisms

Percentage of Bases in Four Organisms

Slide # 9

Source of DNAATGC





Go to Section:

Rosalind franklin the famous picture taker

Rosalind Franklin: The Famous Picture Taker

Slide # 10

  • 1952: Rosalind Franklin: an expert in x-ray crystallography.

  • She took the x-ray picture of DNA -- shows DNA is a double helix.

  • 1958: Franklin died (37 years old)

James watson francis crick puzzle solvers

James Watson & Francis Crick: Puzzle Solvers

Slide # 11

  • 1953: Discovered the structure of DNA

  • Described DNA as a doublehelix (twisted ladder)

    • Sides of ladder are made up of sugar & phosphate groups

    • Steps of ladder are made up of nitrogen base pairs (A-T & C-G)

      -- Applied Chargaff’s rules

    • Base pairs (steps) are held together by weak hydrogen bonds

    • Sequence (order) of nitrogen bases determines the genetic instructions / “genetic code” of organism.

James Watson

Francis Crick

Drill 12


Quote:Whatever you are, be a good one!

Abraham Lincoln

Agenda:Homework check

DNA structure cont.

Cell Division notes


1. Which of the following best describes cellular respiration?

a. External breathing

b. Breakdown of sugar to release energy in cells

c. Movement of water from outside the cell to inside the cell.

d. Removal of water from a cell

2. Describe the structure and components of a DNA nucleotide.

Knowing the structure tells how dna replicates

Knowing the Structure Tells how DNA Replicates

Slide # 12

  • DNA Replication: makes 2 identical DNA strands by copying the original model

  • Each new strand contains one old (parent) strand & one new (daughter) strand

  • DNA replication occurs during cell division – inside the nucleus

Parent strand: gray

Daughter strand: red

Steps in dna replication

Steps in DNA Replication

Slide # 13

  • DNA unwinds (DNA Helicase)

  • DNA polymerase breaks hydrogen bonds that hold nitrogen bases together

  • DNA ligase hydrogen bond new nitrogen bases onto DNA parent strand

    • Chargaff’s rules applied: A-T & C-G

    • Nucleotides added in 5’ to 3’ direction

  • Sugar-phosphate groups bond to nitrogen bases to complete daughter strand

  • Result: 2 identical DNA strands each contains 1 parent strand & 1 daughter strand

Steps in dna replication1

Steps in DNA Replication

Slide # 14

Parent strand

Daughter strand

Strands are antiparallel

When does replication occur

When Does Replication Occur?

Slide # 15

  • 1. The cell replicates (makes a copy) its DNA right before cell division.

  • 2. When two new cells are produced in cell division, each new cell needs its own copy of the DNA (identical copy!)

  • 3. After DNA replication, the cell will divide in half (cell division) and give each new cell a copy of the DNA



Slide # 16

  • Fertilized human egg cell has 46 chromosomes

    • 23 chromosomes in egg cell

    • 23 chromosomes in sperm cell

    • Humans have 46 chromosomes in each body cell.

  • 2. Each cell has millions of base pairs storing our genetic code.

  • 3. After DNA Replication, each cell has 92 “sister chromatids”

    • After mitosis, each cell ends up with 46 chromosomes

Karyotype of Human


Chromosomes more than just dna

Slide # 17

Chromosomes: More than Just DNA

Chromosome:coiled DNA & protein “spacers” called histones.

Histones keep the chromosome from getting tangled.

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