Chapter 8 DNA Structure and Function

Watson & Crick

  • Watson and Crick are most popularly known for their double he lix model of DNA, not for discovering DNA.
  • The pair won the Noble Prize in 1962, but there colleague Rosalind Franklin died before they were awarded it, so she is not given as much credit
  • Their 3 dimensional model changed the way people saw DNA and opened up new pathways of research.

Chargaff's Rules

  • Erwin Chargaff made 2 rules essential to future research in DNA
  • His first rule said that there is the same amount of guanine (G) as cytosine (C), and the same amount of adenine (A) as thymine (T)
  • His second rule said that the DNA of different species differs in its proportions of guanine to adenine

How Do DNA Base Pairs Bind?

This image shows the bases pairs binding
  • As said in Chargaff's first law, only adenine and thymine can bind, and guanine and cytosine can bind
  • The bases bind together from hydrogen bonds formed between them
  • Each half of the helix is complementary to the other half, allowing only them to bond

What is a Chromosome?

  • Chromosomes are structures that holds a single DNA molecule for the organism
  • Chromosomes are essential to reproduction because they hold all of the DNA needed for that organism.
  • They go through DNA replication

What is a Karyotype?

An example of a Karyotype
  • A Karyotype is an organized profile of a persons set of chromosomes
  • It is a visual representation used for experiments and lab work
  • The Karyotype is organized by size and shape

How Does DNA Replicate?

  • DNA replication is when cell copies chromosomes so that it has two sets. This is done to prepare for division
  • The first step is to break the bonds holding the two helixs together. This unravels the two strands
  • Then primers are attached to each strand, which helps the enzyme DNA polymerase add on nucleotides to form the 2 new DNA double strands.
  • The original strands are called the parental strands, and the newly synthesized are called daughter strands
  • Then, the primers are removed and replaced with nucleotides by the enzyme DNA ligase to make the finished product
  • A strand of DNA has a 3' carbon at the top of the nucleotide and a 5' carbon at the bottom, and in a double helix of DNA each strand runes opposite one another.
  • New nucleotides can only be attached to a 3', so they are synthesized 3'-5', but read 5'-3

What Damages DNA?

UV light
  • Sometimes mistakes happen during DNA replication, such as adding the wrong base, or to many or to little nucleotides are added
  • Usually they are corrected, but ehen the damages become permanent they become mutations
  • Other damages to DNA can come from UV light, x-rays, and gamma rays

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