DNA and Genes
The Structure of DNA
• DNA is a type of nucleic acid
• DNA is made of subunits called nucleotides
• Strand of DNA looks like a 3D-double helix
shape
• Nucleotides have 3 parts (will draw this on next
slide)
– 1.Sugar
• 5 C sugar called deoxyribose
– 2.Phosphate group
– 3.Nitrogen Base (4 different types)
•
•
•
•
Adenine (A)
Guanine (G)
Thymine (T)
Cytosine (C)
Base pairing rules
• 1 molecule of human DNA contains billions of
nucleotides
• Adenine=Thymine
• Guanine=Cytosine
These are known as Chargaff’s rules
The DNA Song
(to the tune of Row, Row, Row your Boat)
• We love DNA
• Made of nucleotides.
• Sugar, phosphate, and a base,
• Bonded down one side.
•
• Adenine and thymine
• Make a lovely pair,
• Cytosine without guanine
• Would feel very bare.
•
• (author unknown)
•
•
The Double Helix
• Watson and Crick
• 2 strands of DNA wind around each other–
twisted – like a twisted ladder
• They fit together using base pairs and have a
sugar-phospate backbone
• What if one strand is ACACAC, what would the
other strand be?
• +++++++++++++++++++++++++++++++++++
summary
• The DNA molecule is a long chain of subunits
called nucleotides. Each nucleotide is made of a
phosphate group, the five-carbon sugar
deoxyribose, and one of the four different
nitrogen bases.
• Stop**********************************
QSR #3
• 1. What are the 3 parts of a nucleotide?___________,
_____________, _______________.
• 2. a. DNA is in a ____ ____ shape.
•
b. _______ & _______ discovered this shape.
• 3. What are the base pairing rules for nucleotides?
• 4. If one strand of DNA is ACGTAGCTAG, the
complementary strand = _________________.
Replication of DNA
• Process by which DNA is copied within the
NUCLEUS….during which phase? __________
• Single strand serves as a “template” or pattern for
next strand
• Can occur over and over again
Steps of Replication (S-Phase)
– 1. Helicase (an enzyme) unzips the helix into separate
strands
– 2. Forms a “bubble” where it’s replicating
– 3. Another enzyme, DNA Polymerase, pairs free
nucleotides to the template
– 4. Now have two identical strands of DNA that are
ready to start cell division (mitosis)…each with an old
strand of DNA & a new strand of DNA
Replication of DNA
• DNA Polymerase:
– Allows for “proofreading”– if a wrong nucleotide gets
added, DNA polymerase removes it and adds the
correct one
Summary
• In DNA replication, enzymes work to unwind and
separate the double helix and add complementary
bases to the exposed strands. Each new double
helix is composed of one old DNA strand and one
new DNA strand.
QSR #4
• 1. a. When would a DNA molecule need to replicate
itself?
• ____________________ b. and in what stage does this
occur?________________________
• 2. What would you call a molecule with a RIBOSE sugar
and THREE phosphate groups?_____
• 3. If a DNA molecule is 40% cytosine, what % is
thymine?_________
• 4. Define replication.____________________________
• _____________________________________________
• 5. DNA _________ adds free nucleotides to the parental
strand of DNA, then “___________” to make sure its
done correctly.
QSR #5
• 1. Fill in the blanks of the following paragraph:
– Steps of replication: The _________ enzyme unzips
the double stranded ______. A __________ forms
where this occurs. DNA______________, another
enzyme, adds the correct _____________ to both of
the unwinded strands. It also acts as a
_______________...it corrects incorrect nucleotides.
There are now ____ strands of exact copies of ______.
“Central Dogma” of Molecular Biology
• States that information flows from DNA, to RNA,
then to proteins being made.
RNA
• Like DNA, RNA is made of nucleotides (sugar,
phosphate, and base)
• It is a “temporary copy” of DNA that is used, then
destroyed
• Single-stranded – RIBONUCLEIC ACID
• Why is RNA needed?_____________________
Transcription
• A process that uses “some” DNA to make a
complimentary single strand of RNA
3 Types of RNA
• Messenger RNA (mRNA)
– The message in DNA is rewritten in this form INSIDE
THE NUCLEUS and taken to the ribosome
• Transfer RNA (tRNA)
– Transfers amino acids within a ribosome to make
proteins.
• Ribosomal RNA (rRNA)
– The ribosomes that actually make the protein
– (ribosomes are made or RNA and PROTEIN)
Transcription Steps:
****Same steps as replication to make RNA:
–
–
–
–
1. RNA polymerase unzips the DNA
2. use template to make a complementary base-pair
3. RNA polymerase “Proofreads” RNA base pairs
4. this new single strand of mRNA detaches from the
DNA, and the DNA “zips”back up
– 5. FINAL STEP: RNA strand ( called mRNA) can
now leave the nucleus and be “translated” into a
protein
DNA is the blueprint for Proteins
Transcription
• DNA is found in the nucleus, but is too big to
leave the nucleus
– BUT….DNA has the instructions to make proteins
– AND, protein synthesis takes place at the ribosome—
(cytoplasm/Rough ER)
• How does the information get from nucleus to
ribosome?---mRNA
• +++++++++++++++++++++++++++++++++++
QSR #6
• 1. The _____ ______ of molecular biology states that info flows
from DNA, to RNA, to proteins.
• 2. Ribonucleic acid is also called ____ for short.
• 3. _______ is the process of copying a strand of DNA to make a
mRNA.
• 4. Very important enzymes involved in DNA/RNA synthesis are
__________(s).
• 5. What’s the point for making RNA?_______________________
• 6. How do DNA instructions get from the nucleus to the ribosome?
___________
The difference
(between DNA & RNA)
• *****1. U replaces T in RNA…”Uracil” binds now with
adenine…
• 2. Also the sugar in RNA is ribose, not deoxyribose
• 3. Remember that RNA is only a SINGLE STRAND!!!
• 4. RNA IS ONLY TEMPORARY!!!!
– If a DNA segment = AGCCTAA, what would be the mRNA
molecule?__________________
Review before notes:
• 1.True or false…DNA can leave the nucleus, taking its
genetic info with it in order to make some proteins.
• 2. Why does a cell make lots of RNA but only one copy
of DNA?
• 3. What would be the complimentary strand of RNA if
the DNA sequence is ACCTTTGAAA?
• 4. What happens to the DNA molecule once it makes a
strand of RNA?
Translation
• A lot of DNA is nonsense and codes for nothing –
“junk DNA” or “INTRONS”
• “EXONS” are regions of DNA that do code for
proteins
• Translation: the process of “translating” info
from mRNA to make a protein.
– This occurs on ribosomes!!!
– Where does transcription take place? ____________
Practice
• Original DNA segment: ACCGTATTATTACGG
• Complimentary mRNA: ____________________
– What is this called?___________________________
• Complimentary tRNA: _____________________
– What is this called? ___________________________
• So how does tRNA compare to DNA?
• +++++++++++++++++++++++++++++++++++
Translation…
• Codon: 3 nucleotides make up a “word”
• Example: Serine (Amino Acid) have the codons
UCU, UCC, UCA, UCG
– 1Start codon: AUG -- signal for start of translation
– 3 Stop codons: UGA, UAA, UAG -- signal for
stop/end of amino acid chain
• (look at handout)
Use your worksheet…
• What Amino Acid is coded by GGA? UGG?
ACU?
• Amino acids are then linked together to become a
___________, which then is used to build the
entire organism
• ****20 amino acids make up a protein****
• +++++++++++++++++++++++++++++++++++
Genetic Changes
• Mutation
– Any change in the DNA sequence that also changes
the protein it codes for
• ***Mutations in reproductive cells WILL be
passed to offspring
• ***Mutations in body cells could cause problems
for the individual but WILL NOT be passed
to offspring
Point Mutations
• A change in a single base pair in DNA
• THE DOG BIT THE CAR
• THE DOG BIT THE CAT
– GGC CHANGES TO AGC
– GLY CHANGES TO SER
• CAN EFFECT THE ENTIRE FUNCTION OF
THE PROTEIN
– ****Least harmful of the mutations****
Frameshift Mutations
• A mutation in which a single base is added or
deleted
• THE DOG BIT THE CAT
• THE DOB ITT HEC AT
• Every codon after the addition or deletion is
effected
Causes of Mutations
• 1. Mutagens—agents in the environment that can
change DNA…ex: UV from sun
– Any agent that can cause cancer
• 2. Radiation
– X-rays
– Cosmic ray
– UV rays
Causes of Mutations
• 3. Chemicals
– Asbestos
– Cyanide
– formaldehyde
• 4. High temperatures
Repairing DNA
• Enzymes proofread DNA and replace incorrect
nucleotides with correct nucleotides
– DNA polymerase
– RNA polymerase
Study Guide
Structure of DNA
1. nucleotides
2. Base pairing rules
3. Double helix
•
Replication
Transcription
•
translation
•
Mutations
• ***know all your notes and QSR!!!