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DNA / Protein Synthesis. History of DNA Research. DNA – Deoxyribonucleic acid 1) Frederick Griffith (1928)- discovered that a factor in heat-killed, disease-causing bacteria can “transform” harmless bacteria into ones that can cause disease. Griffith's Experiments

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DNA / Protein Synthesis

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DNA / Protein Synthesis


History of DNA Research

DNA – Deoxyribonucleic acid

1) Frederick Griffith (1928)- discovered that a factor in heat-killed, disease-causing bacteria can “transform” harmless bacteria into ones that can cause disease.


  • Griffith's Experiments

    • Griffith set up four individual experiments.

    • Experiment 1: Mice were injected with the disease-causing strain of bacteria. The mice developed pneumonia and died.


Harmless bacteria (rough colonies)

  • Experiment 2: Mice were injected with the harmless strain of bacteria. These mice didn’t get sick.

Lives


  • Experiment 3: Griffith heated the disease-causing bacteria. He then injected the heat-killed bacteria into the mice. The mice survived.

Heat-killed disease-causing bacteria (smooth colonies)

Lives


Heat-killed disease-causing bacteria (smooth colonies)

  • Experiment 4: Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria and injected the mixture into the mice. The mice developed pneumonia and died.

Harmless bacteria (rough colonies)

Live disease-causing bacteria(smooth colonies)

Dies of pneumonia


Heat-killed disease-causing bacteria (smooth colonies)

  • Griffith concluded that the heat-killed bacteria passed their disease-causing ability to the harmless strain.

Harmless bacteria (rough colonies)

Live disease-causing bacteria(smooth colonies)

Dies of pneumonia


  • Transformation 

    • Griffith called this process transformation because one strain of bacteria (the harmless strain) had changed permanently into another (the disease-causing strain).

    • Griffith hypothesized that a factor must contain information that could change harmless bacteria into disease-causing ones.


History of DNA Research

2) Oswald Avery (1944)- discovered DNA was responsible for transformation


History of DNA Research

3) Hershey and Chase (1952)- their studies supported Avery’s work by studying bacteriophage (a virus that infects bacteria)


History of DNA Research

4) Watson and Crick (1953)- first to develop a double-helix model of DNA


DNA

  • DNA is found inside the nucleus of every cell in your body


DNA Structure

  • DNA is made up of nucleotides.

Nitrogenous

Base

Phosphate

Sugar


Parts of a nucleotide

  • A nucleotide contains three parts:

    1) Phosphate group

    2) 5-carbon sugar group (deoxyribose)

    3) Nitrogenous bases (4 types)

    • Adenine (A)

    • Guanine (G) Purines (double rings)

    • Cytosine (C)

    • Thymine (T) Pyrimidines (single ring)

To help you remember:

CUT = PY


Chargaff’s Rule

  • Erwin Chargaff (1949) discovered the base-pairing rules for nitrogenous bases:

    1) A always pairs with T

    C always pairs with G

    2) % A in DNA = % T in DNA

    % C in DNA = % G in DNA


Guanine

Cytosine

Adenine

Thymine


  • Double Helix

    • DNA molecule is composed of two long chains of nucleotides twisted and held together by hydrogen bonds in the center between the nitrogen bases


  • DNA Double Helix


  • In even in your smallest chromosome there are 30 million base pairs. How does so much DNA fit in every tiny cell in your body?


DNA

  • You fold it!

  • Think about how much easier it is to pack your suitcase when everything is nicely folded.

Can’t fit

Much more fits when you organize and fold it.


  • DNA must condense (make itself smaller) by folding itself around proteins called Histones.

  • When DNA wraps around Histones it forms tight coils and is called chromatin.


  • What are histones?

  • Histones are proteins that DNA wraps around.

  • What is Chromatin?

  • Chromatin is what you call DNA when it is wrapped around the Histones.


Example:

Histone

DNA

Double Helix

Chromatin

DNA around histones


Chromosomes

  • When the chromatin forms coils and condenses it forms a chromosome.

  • See Fig. 12-10 in your book.


DNA

Double Helix

Chromosomes

Made up of chromatin

Chromatin

DNA around histones

Histone =


  • DNA Double Helix  Chromatin  Chromosome

DNA Double Helix

DNA Chromatin

DNA Chromosome

http://www.biostudio.com/demo_freeman_dna_coiling.htm (dna coiling)


DNA Replication

  • Occurs when cells divide.

    (Cell division)


DNA Replication

  • DNA makes an exact copy of itself

  • takes place inside the nucleus during S phase before cell division


Replication

  • Each strand of the double helix of DNA serves as a template against which the new strand is made.


phosphate

Sugar-phosphate

Sugar-phosph

DNA Base Pairing Rules

  • A compliments T

  • T compliments A

  • G compliments C

  • C compliments G

G

A

C

T

T

C

A

A

G

T


Replication

Step 1: The hydrogen bonds between the double helix break and two strands separate. Each strand is called a template strand.

Step 2: Two new complementary strands are formed following the rules of base pairing. The new strands are called complimentary strands.

Template strand

Compliment strand


DNA Polymerase

A

T

How DNA Replication Works!

DNA polymerase is an enzyme that adds the complimentary bases to the DNA template strand and also “proofreads” or checks that it is correct.


Semiconservative


Replication

  • Template Strand (original)

  • CGTATCCGGAATTT

  • The complimentary strand..

  • GCATAGGCCTTAAA


Template strand

Complimentary Strand

ACGGCAT

TACGGCAT

TGCCGTA

ATGCCGTA


Complimentary

  • If I have a strand that DNA sequence of CAT what would be on the complimentary strand?

  • CAT

GTA


RNA

  • Ribonucleic acid

  • Single strand

  • made up of nucleotides

  • contains three parts:

    • 1) Phosphate group

    • 2) 5-carbon sugar group (ribose)

    • 3) Nitrogenous bases (4 types)

      • Adenine (A)

      • Guanine (G) Purines (double rings)

      • Cytosine (C)

      • Uracil (U) Pyrimidines (single ring)


Base-pairing in RNA

1) A always pairs with U

2) C always pairs with G


Types of RNA


Compare DNA and RNA

1) Sugars are different:

DeoxyriboseRibose

H OH OH OH

HOH OH OH


Compare DNA and RNA

DNARNA

2) A, G, C,TA, G, C, U

(A–T, C-G) (A-U, C-G)

3) Double strandedSingle stranded

4) only 1 type3 types


Protein

  • Proteins are made of building blocks called amino acids.

  • Proteins are different from one another by the sequence, or order, of their amino acids.


Protein

  • There are 20 different amino acids.

  • Thousands of proteins can be made from these amino acids because there are many different orders that they can be in.


  • Proteins are made in two steps:

    • Transcription

    • Translation


  • What is transcription?

    • The process where mRNA is made from a DNA template

    • Transcription happens in the nucleus


  • What is translation?

    • Translation is the decoding of an mRNA message into a protein.

    • Translation takes place on ribosomes in the cytoplasm


Transcription Translation


Transcription

  • Protein synthesis begins when a strand of (A) DNA unravels.

  • The code for producing a protein is carried in the sequence of the (B) bases in the DNA.

  • Each group of three bases forms a codon, which represents a particular amino acid.


Transcription

  • One of the unwound strands of DNA forms a complementary strand called (C) mRNA.

  • This process is called transcription.

  • It takes place in the nucleus of the cells.


Bases

DNA

mRNA


Post-transcriptional modification

  • DNA is composed of coding and noncoding sequences

  • Noncoding region = Introns

  • Coding region = Exons (code for proteins)

  • During transcription, introns are cleaved and removed, while exons combine to form useful mRNA


Post-transcriptional modification

E I E I E

initial DNA

 introns cleaved

pre-mRNA

 exons combine

final mRNA


Now look at the right side of the picture.

  • The mRNA has moved into the cytoplasm, where it attaches to a (D) ribosome.

  • A phase of protein synthesis called translation then begins.

Ribosome

mRNA


  • A (E) tRNA approaches the ribosome.

  • At one end of this molecule are three bases known as an (F) anticodon.

  • At the ribosome, each anticodon lines up with its complementary codon on the mRNA.

tRNA

Anticodon

Codon

Anticodon


  • This occurs according to base pairing.

  • At the other end of tRNA, an (G) amino acid is attached.

  • As the ribosome moves along the strand of mRNA, new tRNAs are attached.

  • This brings the amino acids close to each other.


  • The amino acids are joined by peptide bonds, and the resulting strand is a protein.


Codon Chart

  • To determine which amino acid we choose we use this chart:

CODONAMINO ACID

AGU

AGC

GGU


  • What are mutations?

    • Mutations are changes in the DNA sequence that affects the genetic information


Types of mutations:

  • Gene mutations result from changes in a single gene

  • Chromosomal mutations involve changes in whole chromosomes


  • Gene mutations:

    • Point mutations – affect only one nucleotide because they occur at a single point

      • Include substitutions, additions, and deletions

    • Frameshift mutations – when a nucleotide is added or deleted and bases are all shifted over, leaving all new codons.

      • Include additions and deletions

      • Substitutions don’t usually cause a frameshift


Substitutions

One base change


Insertions

Many base changes


Deletions


  • Chromosomal mutations:

    • Include deletions, duplications, inversions, and translocations.


  • Deletions involve the loss of all or part of a chromosome.


  • Duplications produce extra copies of parts of a chromosome.


  • Inversions reverse the direction of parts of chromosomes.


  • Translocations occurs when part of one chromosome breaks off and attaches to another.


  • Significance of Mutations

    • Many mutations have little or no effect on gene expression.

    • Some mutations are the cause of genetic disorders.


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