DNA and the Language of Life Chapter 11

How did scientists learned that DNA is the genetic material?

Genes are Made of DNA  Griffin’s experiment (1928)  Avery’s experiment (1944)  Hershey and Chase experiment (1952)

Griffith’s experiment

 Griffith showed that although a deadly strain of bacteria could be made harmless by heating it, some factor in that strain is still able to change other harmless bacteria into deadly ones. He called this the "transforming factor."

Avery’s experiment  Transforming factor - Protein or DNA? Avery and colleagues treated a mixture of heat- treated deadly strain and harmless strain of bacteria with:  Protein-destroying enzyme  DNA-destroying enzyme

Hershey and Chase experiment -1952

 The basic unit of the DNA molecule is called: NUCLEOTIDE

A NUCLEOTIDE has three parts:  A ring-shaped sugar called deoxyribose  A phosphate group  A nitrogenous base (single or double ring of carbon and nitrogen atoms)

Nitrogenous Bases

Nucleotide monomers join together by covalent bonds between the sugar of one nucleotide and the phosphate of the next, forming a sugar- phosphate backbone.

The bases pair up (A- T & G-C) forming the double helix first described by Watson and Crick

Watson, Crick and Franklin

Various ways to model DNA structure manipulate DNAhttp://

Why does DNA need to be replicated? Growth – new cells - reproduction How does this process happens?

 Weak bonds  Hydrogen bonds  Comes apart easily  Comes together easily

Overview of DNA replication  DNA separates  Complementary nucleotides are linked along separated strands

initiate  Initiator protein guides unzipper protein (helicase) to correct position on DNA

untwister  Untwister (topoisomerase) unwinds the DNA double helix in advance of the unzipper

Unzipper separates DNA strands, breaking weak bonds between the nucleotides unzip

assemble Builders (polymerases) assemble new DNA strand by joining nucleotides to their matching complements on the exposed strands

straightners  Straighteners (single-strand DNA binding proteins) keep single strand of DNA from tangling

Phosphate provides energy Phosphate bond energy from the new nucleotides is used to make the new bonds

Leading vs. Lagging strand  Leading (top) strand is built continuously as the builder follows behind the unzipper, but the Lagging (lower) strand builds in the opposite direction

Lagging strand  Lagging (lower) builder makes a loop with the DNA strand and builds in opposite direction

Lagging strand  Built in small sections  Sections linked by enzyme ligase

Repairs of DNA  Erasers (Repair Nuclease): find poorly matched or damaged nucleotides and cut them out

Repairs of DNA  Builders (Polymerase): fill gaps using other DNA strand as a guide

Repairs of DNA  Stitchers (Ligase): uses ATP to restore continuity of backbone of repaired strand

Big picture of DNA replication

Replication review

REPLICATION IN 3 STEPS

Conection between DNA and Protein  DNA defines the genotype (genetic makeup)  Proteins determine the phenotype (specific trait)  Each gene codes for one protein (polypeptide)

Life is orchestrated by Proteins Proteins  Combinations of 20 different amino acids linked in long chains  Function is determined by amino acid sequence  Amino acid sequence is determined by DNA sequence  Used for enzymes, hair, muscles, cell parts

Amino Acids Linked  Amino Acids Link Together to Form a Protein (Polypeptide)

DNA to Protein Conection  Geneticists Beadle and Tatum studied mutant strain of orange mold  This strain was missing a necessary enzyme for mold to grow  Each mutant strain was defective in a single gene  One gene-on enzyme hypothesis  More accurate – One gene one polypeptide

Protein Synthesis  DNA → RNA → Protein (polypeptide)  This happens in two main steps:  Transcription  Translation

Information is sent from the Nucleus to ribosome where protein is made

Outline of making Protein  Directions on DNA  DNA opens up and messenger RNA (mRNA) copies message  mRNA is edited – some parts taken out (introns)  mRNA goes out of nucleus to ribosome  mRNA attaches to ribosome  Transfer RNA (tRNA) picks up an amino acid  tRNA attaches to mRNA matching complementary base pairs at opposite end from amino acid  Amino acid is attached to other amino acids held by the ribosome to make a chain of protein  When protein completely built unattached from ribosome

Why we need RNA?  DNA cannot leave the nucleus  DNA gets transcribe into Messenger RNA (mRNA)  Once edited, mRNA can leave the nucleus as a single strand

Similarities and differences DNA vs. RNA  k/mcvittiej/bio30unit1/overheads/1.23.htm k/mcvittiej/bio30unit1/overheads/1.23.htm k/mcvittiej/bio30unit1/overheads/1.23.htm

1.A sequence of nucleotides In DNA (a gene) is transcribed to RNA in the nucleus 2. The RNA travels to the cytoplasm where it is translated into the specific amino acid sequece of a polypeptid

A codon is a three- base "word" that codes for one amino acid. Several codons form a "sentence" that translates into a polypeptide.

Transcription players  DNA  Messenger RNA (mRNA)  RNA polymerase

Transcription

mRNA editing

Translation players  mRNA  Transfer RNA  Ribosome  Ribosomal RNA

Translation

Transcription-translation animations  imations.html imations.html imations.html

 Protein making analogy short movie /02.html /02.html 00:54 – 03:20

What are Mutations  Any change in the nucleotide sequence of DNA  Two types of mutations  Base substitution  Base deletion

Types of mutations