DNA DNA- Deoxyribonucleic acid A large polymer used to carry
the genetic code of all living organisms
DNA Heredity & Structure What we know about DNA was not
discovered overnight! Many different scientists contributed
information. Because of the efforts of all these scientists, we now
have a model of DNA that consistently fits the observations we
make. It also allows us to make useful predictions!
DNA History Oswald Avery (1944) genes are composed of DNA
Rosalind Franklin (1952) studied the DNA molecule using a technique
called X-ray diffraction HERSHY CHASE DNA & Viruses James
Watson/Francis Crick (1953) Developed the double helix model of DNA
structure
Griffiths Experiment- 1928 Was trying to develop a vaccination
for the pneumococcus bacteria. Vaccine- a prepared substance from
killed or weakened disease causing agents used to prevent future
infections He was working with two strains of bacteria. Rough -
bacteria had a rough appearance in culture, non-virulent (doesn't
kill) Smooth - bacteria had a smooth appearance in culture,
virulent (kills) He discovered that something was being transferred
between the dead smooth bacteria and the living rough bacteria that
caused them to undergo transformation. Avery, MacLeod, McCarthy
identified that DNA was being transferred killing the rats in
1944
Avery, MacLeod and McCarthy- 1944 1. Avery, MacLeod, McCarthy
(1944)- proved that the transfer of DNA is what killed Griffiths
rats 1. took extract (from heated smooth bacteria) and treated it
with DNAase (destroys DNA) - then mixed with rough bacteria and
injected into rats -> the rats lived 2. in other side of
experiment, treated extract with protease (digests proteins) -then
mixed with rough bacteria and injected into rats -> rat died
This showed that DNA, not protein, has ability to transform
cells
Heat-killed, disease-causing bacteria (smooth colonies)
Disease-causing bacteria (smooth colonies) Harmless bacteria (rough
colonies Dies of pneumonia Lives Heat-killed, diseasecausing
bacteria (smooth colonies) Control (no growth) Lives Harmless
bacteria (rough colonies) Dies of pneumonia Live, disease-causing
bacteria (smooth colonies)
Erwin Chargaff- 1950 Base pairing rule is A-T and G-C Thymine
is replaced by Uracil in RNA Bases are bonded to each other by
Hydrogen bonds Discovered because of the relative percent of each
base; (notice that A-T is similar and C-G are similar)
Chargaffs Data Source of DNA A T C G Streptococcus 29.8 31.6
20.5 18 Yeast 31.3 32.9 18.7 17.1 Herring 27.8 27.5 22.2 22.6 Human
30.9 29.4 19.9 19.8
Hershey and Chase- 1952 Hershey and Chase proved that the
genetic material is DNA in 1952. Previously, scientists thought
that proteins were the hereditary molecule Hershey and Chase used
radioactively labeled bacteriophages (viruses) to determine that
DNA was being injected by the viruses instead of proteins. This
proved that DNA was the hereditary material of life.
Martha Chase (left) & Alfred Hershey (right)
Virus Structure DNA is located in the head. The outside and
tail of the virus is made out of protein.
Virus ATTACKS!!
Bacteriophages ATTACK!!
Hershey Chase Experiment DNA in Viruses Bacteriophage with
phosphorus-32 in DNA Bacteriophage with sulfur-35 in protein coat
Phage infects bacterium Phage infects bacterium Radioactivity
inside bacterium No radioactivity inside bacterium
Wilkins & Franklin- 1952 MHF Wilkins and Rosalind Franklin
studied the structure of DNA crystals using X-rays. They found that
the crystals contain regularly repeating subunits. The pattern
generated by the diffraction of the x-rays suggested that the
overall structure of DNA was a double helix.
Watson & Crick- 1953 James Watson and Francis Crick used
Chargaff's base data and Franklins X-ray diffraction data to
construct a model of DNA. Their model showed that DNA is a double
helix with sugar-phosphate backbones on the outside and the paired
nucleotide bases on the inside, in a structure that fit the spacing
estimates from the X-ray diffraction data. The paired bases can
occur in any order, giving an overwhelming diversity of
sequences.
Watson & Crick with their model of DNA
DNA Structure
There are 3 main components of a strand of DNA 1. DNA is a
large polymer (macromolecule) Made up of monomers called
nucleotides. Nucleotides A nucleotide is made of 3 parts: 1. 2. 3.
phosphate functional group Nitrogen base (A, T, G, C) Deoxyribose
sugar (in DNA)
DNA Structure Dna twists into a double helix due to the
attraction between the negatively charged phosphates and net
positive charge of the hydrogen bonds between the Bases - DNA has
an overall negative charge due to the phosphates of the
sugar/phosphate backbone Rails of the ladder are made of
alternating sugar and phosphates The nitrogen base (A, T, G, C) are
always attached to the deoxyribose sugar
Nitrogenous Bases Two types: Purines (two rings) Pyrimidines
(one ring) Purines Adenine and Guanine Pyrimidines Thymine and
Cytosine
Practice Pairing TEMPLATE STRAND A T C G G C G C T A A T
Bonding TEMPLATE STRAND A T C G G C G C T A A T Weak HYDROGEN
bonds form between the Nitrogen Base Pairs.
The backbone of it all TEMPLATE STRAND A T C G G C G C T A A T
The backbone is made of alternating sugars and phosphates. -
Remember: Sugar ALWAYS attaches to the Nitrogen base
Chromosome Coils Supercoils Histones
DNA Replication Part 2
DNA & RNA continued! 1. Before mitosis (during S phase of
interphase) , a complete copy of a cells DNA is made through a
process called DNA replication. 2. When a cell divides, each
daughter cell gets one complete copy of the DNA. 1. Similar to
photocopying a document the end result is two identical documents
that contain the same information.
Step 1 1) DNA must unwind and break the hydrogen bonds. DNA
Helicase unzips the strands. 1. DNA Helicase- the enzyme that
unzips DNA like a zipper so it can be copied. The area where the
DNA is split is called the replication fork.
Step 2 2. Each strand of original DNA is used as a template
(blueprint). DNA Primase flags or marks the spot for it to begin
DNA Primase- Begins DNA replication by attaching a short fragment
of RNA called a primer to the place where replication will begin.
This primer tells DNA polymerase where to start copying DNA
replication Created by DNA Primase Replication Fork
Step 3 1. DNA Polymerase- makes the new strand of DNA like a
copying machine. It can only read in one direction 3 to 5 just like
how we read a page from left to right. As a result, the new strand
it makes is made in the 5 to 3 direction. 1. 2. Leading strand- the
continuous strand that DNA polymerase makes in the 53 direction. It
never stops once it starts until it reads the entire strand of DNA.
DNA replication 5' to 3 Lagging strand- DNA polymerase can only
read in the 3 to 5 direction, it must make the new strand in small
chunks. These small chunks are called Okazaki fragments. They are
normally between Direction of replication 100-200 base pairs long.
2. DNA Ligase- connects okazaki fragments together on the lagging
strand to make a complete strand
1. Because of Chargaffs rule, only the correct, complementary
bases will fit, so chances are good that the DNA polymerase will
make a perfect copy. 2. What would happen if DNA polymerase made a
mistake? How long do you think these animals will survive?
Protein Synthesis Transcription
DNAs Purpose DNA has genes that code for the synthesis
(creation) of specific PROTEINS Heres the problem Where is DNA
located? Nucleus Where does Protein Synthesis occur? At ribosomes
in the cytoplasm Can DNA ever leave the nucleus? No.
RNA Ribonucleic acid Single-stranded Sugar is ribose Thymine is
replaced by URACIL 3 types of RNA 1) Messenger RNA (mRNA) o carries
information from DNA to ribosome 2) Transfer RNA (tRNA) o Carries
amino acids 3) Ribosomal RNA (rRNA) o Makes up ribosomes
RNA can be Messenger RNA also called Ribosomal RNA which
functions to mRNA also called rRNA Carry instructions which
functions to Combine with proteins from to to make up DNA Ribosome
Ribosomes Transfer RNA also called tRNA Bring amino acids to
ribosome
Differences between DNA and RNA RNA Structure: Single stranded
Sugar: Ribose Bases: Adenine Guanine Cytosine Uracil DNA Structure:
Double stranded Sugar: Deoxyribose Bases: Adenine Guanine Cytosine
Thymine
Transcription1. Transcription- creating a strand of mRNA from
an original strand of DNA 1. occurs in the nucleus!!!
Steps of transcription 1. Just as DNA polymerase copies DNA, a
similar enzyme called RNA polymerase makes new RNA from the DNA
strand. 2. RNA polymerase temporarily separates the strands of a
small section of the DNA molecule which exposes some of the bases
of the DNA molecule. 3. Along one strand of the DNA, the RNA
polymerase binds complementary RNA nucleotides to the exposed DNA
bases and makes a strand of mRNA. 1. 2. It is called messenger RNA
because it carries DNAs message out of the nucleus and into the
cytoplasm. mRNA is SINGLE STRANDED! A=U T=A C=G G=C
5. When the RNA polymerase is done reading the gene in the DNA,
it seperates from the DNA 6. The separated DNA strands reconnect,
ready to be read again when necessary. 7. mRNA moves out of the
nucleus and finds a ribosome RNA polymerase mRNA DNA
Translation Translation- (also known as protein synthesis)
making a protein from the instructions found on mRNA. These
instructions are originally found in genes. 1. A gene is a region
of DNA that contains the instructions for making proteins. This is
why we refer to DNA as the blueprints Protein
Where does this happen? Where is the DNA located? Where are
proteins made in the cell?
Genetic Code Genetic code the language of mRNA instructions
(blueprints) Read in three bases (codon) at a time by a ribosome
Codon found on mRNA; consists of three bases (one right after the
other) There are 64 different codons that code for 20 amino acids
Each codon codes for a specific amino acid Ex: Consider the
following RNA sequence: UCGCACGGU The sequence would be read three
base pairs at a time: UCG CAC GGU The codons represent the amino
acids: Serine Histidine - Glycine
Special codons- Start and Stop AUG start codon which codes for
the amino acid Methionine. All protein chains begin with this UAA,
UAG, UGA These three codons are stop codons. When a ribosome
reaches these codons it tells the ribosome to end the protein
chain.
Ribosomes- the protein factory 1. Ribosomes are organelles in
the cell designed to make proteins by reading mRNA made during
transcription 2. Ribosomes are found in two main locations in a
cell1. 2. Rough ER Freely floating in the cytoplasm 3. Ribosomes
are made of rRNA 4. Ribosomes have two main parts or subunits that
attach to mRNA to read it. 5. A ribosome can fit two codons inside
of it at a time
tRNA (transfer RNA) tRNA carries (or transfers) the correct
amino acid to the codon on the mRNA. One end of the tRNA has an
ANTICODON that is paired with the codon on the mRNA strand There
are 1000s of tRNAs floating around in the cytoplasm to be used for
translation
Step 1 of Translation (protein synthesis) 1. mRNA is made
during transcription. It then leaves the nucleus and combines with
a ribosome. The ribosome then reads the mRNA to make a protein
Translation (dont copy) mRNA GUA UCU GUU ACC GUA Codon: a
sequence of 3 nitrogen bases on mRNA that code for 1 amino acid Its
a TRIPLET code Example: This strand of mRNA has 5 codons, so it
would code for 5 amino acids.
Translation (dont copy) mRNA GUA UCU GUU ACC GUA Ribosome The
mRNA molecule travels to the ribosomes where the mRNA codes are
read by the ribosomes Ribosomes hold the mRNA so another type of
RNA, transfer RNA (tRNA) can attach to the mRNA
Step 2 of translation mRNA GUA UCU GUU ACC GUA CA U A G A
Ribosome Covalent bond VAL SER 1. As the ribosome reads down the
mRNA strand, it will pair each mRNA codon with the correct tRNA
anticodon. 2. Remember, only 2 tRNAs can fit in a ribosome at a
time 3. After it has been paired, a covalent bond will form between
the amino acids creating a chain of amino acids also known as a
protein
Translation mRNA GUA UCU GUU ACC GUA CA U A G A CA A
Translation- step 3 The ribosome will read through the entire
strand of mRNA making a protein in the process until it reaches a
stop codon. Once it reaches a stop codon, the ribosome releases the
mRNA and the protein is completed. Protein Synthesis Video
As the ribosome reads the mRNA strand, amino acids linked
together to form a protein. The new protein could become cell part,
an enzyme, a hormone etc.
Protein synthesis in prokaryotes vs eukaryotes Prokaryote vs
eukaryote protein synthesis Prokaryotes lack a nucleus. While RNA
polymerase begins making the strand of mRNA from the template DNA,
the ribosome floating around in the cytoplasm can simultaneously
read the mRNA strand thats being made and translate it into a
protein In Eukaryotes, the mRNA strand must first exit the nucleus
through a nuclear pore before it can be translated into a
protein
Mutations
Point Mutations- Substitutions Point mutations mutations
involving changes in one or a few nucleotides in a DNA sequence.
Point mutations come from a substitution in the copied DNA strand
Substitutions one base is changed to another ATGC AAGC 3 types of
point mutations: Silent mutation- No change in the protein Missense
mutation- changes one amino acid (missense) Sickle-cell anemia is
caused by this Nonsense mutation- Inserts a pre-mature STOP
codon
Frameshift Mutations A frameshift mutation occurs when the
reading frame of the ribosome is changed. How frameshift mutations
can affect the protein: This may change every amino acid that
follows the point of the mutation. Can alter a protein so much that
it cannot perform its function. Frameshift mutations can come from
2 different changes to the DNA sequence Insertion a extra base is
inserted into the original strand of DNA Deletion a base is removed
from the original strand of DNA Frameshift due to insertion
Frameshift due to deletion
Guess the mutation Deletion Substitution Insertion
Significance of mutations Mutations can be neutral, beneficial,
or harmful Neutral mutations Generally have little or no effect on
an organism. Beneficial mutations May produce proteins with new or
altered activities Useful to organisms in different or changing
environments Plant an animal breeders take advantage of these
Polyploidy often results in larger, stronger plants. Bananas and
other citrus fruits have been made polyploid.
Harmful mutations Can cause dramatic change in protein
structure or gene activity Defective proteins can disrupt normal
biological activities May result in genetic disorders Normal Fruit
fly face Antennae replaced by legs
Mutations & Inheritance Mutations in somatic (body) cells
affect only that organism, but the effects can be dramatic. Harmful
mutations cause many forms of cancer. Mutations in gametes (sperm
& egg) are passed along to offspring. These mutations become
the basis for new genetic variation within a species, which is
important to understand evolution.
Chromosomal Mutations Mutations can also occur when a
chromosome is changed. A chromosomal mutation is a change in the
number or structure (genes) of chromosomes. 4 main types of
chromosomal mutations: Deletion Duplication Inversion
Translocation
Deletion Duplication Inversion Translocation
Part 3- Genetic Techniques
What is Genetic Engineering? Genetic Engineering- Making
changes in the DNA code of living organisms in an effort to achieve
a more desirable trait
Techniques in Genetic Engineering DNA extraction Removal of DNA
from a cell Cutting DNA Small sections are cut from the DNA using
Restriction enzymes Separating DNA DNA is separated in a technique
called Gel Electrophoresis (separates according to size) CSI- crime
scene investigation- DNA is often used to link criminals to crime
scenes by matching DNA fingerprints of a suspect with DNA found at
the crime scene. Making Copies Many copies of DNA can be made in a
technique known as Polymerase Chain Reaction (PCR)
Figure Section 13-2 13-6 Gel Electrophoresis DNA plus
restriction enzyme Power source Longer fragments Shorter fragments
Gel Mixture of DNA fragments DNA fingerprinting
Recognition sequence Section 13-2 Restriction Enzymes DNA
sequence Restriction enzyme EcoRI cuts the DNA into fragments.
Sticky end
Recombinant DNA DNA from different species that is cut and
recombined; usually human DNA is cut and combined with bacterial
DNA
Applications of Genetic Engineering Transgenic organisms that
contain genes from other species (recombinant DNA)
Transgenic Microorganisms Reproduce rapidly Easy to grow
Produces a host of important useful substances such as human forms
of proteins such as insulin, growth hormone, and clotting
factor
Figure 13-9 Making Recombinant DNA Recombinant DNA Section 13-3
Gene for human growth hormone Gene for human growth hormone Human
Cell Sticky ends DNA recombination DNA insertion Bacterial Cell
Bacterial chromosome Plasmid Bacterial cell for containing gene for
human growth hormone
Transgenic Animals Used to study genes and improve food supply
Mice have been produced with human genes that make immune system
act similar to human
Transgenic Plant Genetically modified Many contain genes that
produce natural insecticide Others resist weed-killing chemicals
Eventually produce human antibodies
Cloning Member of a population of genetically identical cells
produced from a single cell Cloned sheep DOLLY Ethical and moral
issues
Figure 13-13 Cloning of the First Mammal A donor cell is taken
from a sheeps udder. Donor Nucleus These two cells are fused using
an electric shock. Fused Cell Egg Cell The nucleus of the egg cell
is An egg cell is taken removed. from an adult female sheep. Cloned
Lamb The fused cell begins dividing normally. Embryo The embryo
develops normally into a lambDolly Foster Mother The embryo is
placed in the uterus of a foster mother.
