Download DNA: THE CODE OF LIFE

THE CODE OF LIFE
WHAT DOES DNA DO?
THE GENETIC CODE…
What forms the genetic code?
How does DNA copy itself?
Contributors…
Rosalind Franklin – English Scientist 1951
Maurice Wilkins – New Zealand Biophysicist
Erwin Chargaff – Austro-Hungarian 1950
James Watson – American Biologist 1953
Francis Crick – English Physicist 1953
…DNA contains the genetic information for cells to
make proteins, which contribute to inherited traits
The structure of DNA
DNA – deoxyribonucleic acid
Resembles a twisted ladder
Referred to as a “double helix”
The structure of DNA
There are three major components of DNA:
• Deoxyribose sugar
• Phosphate group
• Nitrogen bases
The structure of DNA
The “sides” of the ladder or double helix are composed
of alternating:
• Deoxyribose sugar
• Phosphate group
Creating the “Backbone” of the DNA strand
Deoxyribose sugar
Phosphate group
The structure of DNA
The “rungs” of the ladder or double helix are composed of:
4 Nitrogen bases:
• Molecules made of nitrogen, carbon, oxygen, and hydrogen
• The two-carbon nitrogen ring bases (adenine and guanine) are
purines
• The one-carbon nitrogen ring bases (thymine and cytosine) are
pyrimidines.
Nitrogen bases
Nitrogen bases…
Thymine always pairs with Adenine
Cytosine always pairs with Guanine
The structure of DNA
Nucleotides:
• Nucleotides are the building blocks of nucleic acids.
• They are composed of a nitrogenous base, a five-carbon
sugar (deoxyribose or ribose), and at least one phosphate
group.
• A nucleotide forms the “side” and half the “rung” of the
double helix.
Chromosomes, Genes, and DNA
• A gene is a sequence of DNA that determines a trait and is
passed from parent to offspring.
• Each gene is located at a specific place on a chromosome.
• There are many possible combinations of nitrogen bases and
genes, making each organism unique.
Chromosomes, Genes, and DNA
• A gene contains the information to code for one specific protein.
• Proteins within an organism are also responsible for structure,
function, regulation and reproduction within an organism.
• Proteins determine a variety of traits in organisms, from eye
color to an organism’s ability to digest food.
Chromosomes, Genes, and DNA
• The order of the nitrogen bases along a gene forms a genetic code
the specifies what type of protein will be produced.
• REMEMBER????? Proteins are long-chain organic macromolecules
made of individual amino acids.
• A group of 3 nitrogen bases codes for one specific amino acid. This
is known as a CODON. (a sequence of three nucleotides that together
form a unit of genetic code in a DNA or RNA molecule.)
Chromosomes, Genes, and DNA
• The order of the codons determines in which order the
amino acids are assembled to form a specific protein
• There are 20 amino acids, BUT different combinations of
these can form thousands of different proteins.
• 9 essential amino acids for humans cannot be made within
the body, so they must be obtained through diet.
DNA Replication
• The process by which an identical copy of DNA is formed for
a new cell through cell division is DNA REPLICATION.
• Daughter cells must have a complete and exact copy of the
parent cell’s DNA to survive and function properly.
• REMEMBER??? DNA REPLICATION TAKES PLACE IN CELL
DIVISION AND THE FIRST STAGE OF MEIOSIS
Steps of DNA Replication
1. The two sides of the DNA separate between the nitrogen base pairs.
(Much like unzipping a zipper.)
2. Loose nitrogen bases and/or nucleotides within the nucleus pair
with their corresponding nitrogen base on each half of the original
DNA strand.
3. Because of the way the nitrogen bases pair up, the order of the
bases in each new DNA strand matches the order in the original
DNA strand exactly...THE RESULT: TWO IDENTICAL DNA STRANDS
Steps of DNA Replication
Steps of DNA Replication
DNA Replication
How cells make proteins…
How does a cell make proteins?
The structure of proteins
• Remember, the 20 amino acids, in different combinations, can
form thousands of proteins.
• A change in the type or sequence of amino acids will result in a
different protein.
• PROTEIN SYNTHESIS OCCURS IN THE CYTOPLASM, OUTSIDE THE
CELLS NUCLEUS…HOW… IF THE DNA IS INSIDE THE NUCLEUS????
RNA… RIBONUCLEIC ACID
Although both DNA and RNA are nucleic acids, there are some
differences…
• RNA has ribose sugar instead of deoxyribose sugar
Can you see the
difference
between the two
sugars?
RNA…
RIBONUCLEIC ACID
• RNA is a single strand
RNA… RIBONUCLEIC ACID
• In RNA, Uracil replaces Thymine, pairing with Adenine
Two types of RNA…
Messenger RNA (mRNA)
• Copies the message from the DNA in the nucleus and carries
the message to the ribosomes in the cytoplasm.
Transfer RNA (tRNA)
• Carries amino acids to the ribosomes and adds them to the
growing protein.
• Codons of 3 nucleotides determine the specific amino acid
Protein synthesis…
STEP 1: mRNA enters the cytoplasm:
• DNA in the nucleus unzips and usually one (or sometimes both
strands) acts as a template in the formation of mRNA.
• RNA nucleotides, containing ribose sugar, bond with the DNA
strands; Uracil replaces Thymine, pairing with Adenine.
• Once the mRNA is formed, the DNA zips back together again
Protein synthesis…
CONTINUED STEP 1:
TRANSCRIPTION:
• THE PROCESS OF MAKING RNA FROM DNA
AND THE MOVEMENT OF THE RNA FROM THE
NUCLEUS TO THE CYTOPLASM
Protein synthesis…
STEP 2: Ribosomes attach to the mRNA:
• mRNA attaches to a ribosome in the cytoplasm.
• On the ribosome, the mRNA provides the code for the specific
protein that will be made.
• tRNA, with their specific amino acids attached, move into the
ribosome.
Protein synthesis…
STEP 3: tRNA attaches to mRNA in the ribosome
• In the ribosome, molecules of tRNA and the attached
amino acids “read” the message and attach to the
corresponding nitrogen bases on the mRNA
Protein synthesis…
STEP 4: Amino acids join in the ribosome
• One at a time, tRNA attach to the ribosome, continuing to
read the message on the mRNA.
• The amino acids are linked together, forming a ever-growing
chain.
• The amino acid order is determined by the order of the three base codes (CODONS) on the mRNA.
Protein synthesis…
STEP 5: Protein chain forms
• The protein grows as additional amino acids are added when
the ribosome continues to move along the mRNA.
• Once the amino acid is added, the tRNA is released and picks
up another amino acid of the same kind.
• The protein continues to grow until a CODON signals it to stop;
the protein is then released.
Protein synthesis…
CONTINUED STEP 5:
TRANSLATION:
• THE PROCESS WHERE mRNA WORKS WITH tRNA AND
RIBOSOMES AND DIRECTIONS ARE USED TO MAKE A
PROTEIN FROM AMINO ACIDS
• HAPPENS IN THE CYTOPLASM IN RIBOSOMES
Mutations…
How can mutations affect an
organism?
How is cancer related to mutations
and the cell cycle?
Mutations…
MUTATION – any change in the DNA of a chromosome
• Mutations can cause the cell to produce an incorrect protein
during protein synthesis, resulting in a trait being different than
normally inherited.
• Mutations in body (somatic cells) will not be passed to the
offspring
• BUT if a mutation occurs in a sex cell, it can be passed to the
offspring and affect the trait in the offspring.
Types of mutations…
Small mutations that can occur during replication:
• A nitrogen base pair is added
• A nitrogen base pair is substituted for another
• A nitrogen base pair is deleted
Other mutations can result if the chromosomes do not
separate properly during meiosis (formation of sex cells),
resulting in too many or too few chromosomes, or extra
segments of chromosomes
Types of mutations…
Mutations can also be caused by environmental factors.
• Radiation
Mutations
caused by
radiation
Types of mutations…
• Exposure to chemicals
The drug Thalidomide…
• Introduced in the late
1950s as a non-habit
forming sleep-aide.
• Later given to women
experiencing morning
sickness during
pregnancy
• Window of harm
identified during the
first trimester
• Children born with
shortened, absent, or
Types of mutations…
Mutations…
Mutations can be:
• Harmful (if it reduces the organism’s chances for
reproduction and survival)
Good and
• Helpful/beneficial
 Sickle cell carrier and malaria
 Bacteria resistant to antibiotics
bad!!!
• Neither…neutral
The organism’s environment influences whether a
mutation is necessarily harmful or beneficial.
Cancer and mutations…
CANCER – a disease in which some body cells grow and divide
uncontrollably, damaging the parts of the body around them
• There are over 100 types of cancer.
• It affects humans all over the world, as well as other organisms.
• It is often named for the place they begin.
• Cancer can overrun normal cells.
Cancer and mutations…
The are different contributing factors which determine if a person gets
a type of cancer.
• Some inherited traits make it more likely for an individual to
develop certain cancers. (Predisposed)
• Environmental/exposure to chemicals factors can lead to cancer
 Carcinogens – cancer-causing agents
 Ultraviolet rays of the sun – skin cancer
 Toxins in the air and water
• Life-style choices
 Smoking or chewing tobacco
The development of cancer…
• Scientists believe cancer begins when mutations disrupt the normal
cell cycle, which causes cells to divide in an uncontrolled way.
• Tumors form as uncontrolled reproduction and growth of abnormal
cells continues, resulting in a mass of abnormal cells.
• Some cancers and tumors progress very rapidly, others more slowly.
• Cancers can metastasize, which occurs when cancer cells break off
from the original tumor and travel via the blood stream or lymphatic
system, and grow in another location within the organism.
Cancer treatments…
Surgery
• When cancer is contained to one area, as in a tumor, and hasn’t spread, doctors
can remove the cancerous tumor.
• Often, the patient is cured.
Radiation
• If the cancer has spread to adjoining tissues or the tumor cannot be successfully
removed, doctors may use radiation.
• High-energy waves or particles, such as X-rays or Gamma rays, are used to
damage or destroy the cancer cells.
• Cancer cells are affected before normal cells, though damage can also occur to
the normal cells
• Radiation is often used along with surgery and chemotherapy.
Cancer treatments…
Chemotherapy
• The use of drugs to cure a disease is know as chemotherapy
• Cancer-fighting drugs are given and are carried through the bloodstream in
hopes of killing or slowing the growth of cancer cells.
• Often normal cells are also affected.
Cancer treatments…
Side effects of cancer treatment:
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Eating problems, appetite loss, nausea and vomiting
Hair loss
SCIENTISTS ARE
Fatigue and sleeping disorders
CONTINUOUSLY WORKING
Bleeding and bruising
TO UNDERSTAND THE
Skin conditions
General weakness
MECHANISMS OF CANCER,
Susceptibility to infection
HOW TO SLOW CANCER
Mood changes
CELL GROWTH, AS
Elimination problems
WELL AS A CURE.