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Warm-up 4/9/12 Proteins
• What are proteins composed of? (building
blocks)
• Name one function of proteins
DNA Unit Answers
Sec. 12.1 DNA Basics
1. Draw a nucleotide. What are the
four different bases they can contain?
•
•
•
•
P-S-A
P-S-T
P-S-G
P-S-C
P = Phosphate
S = Deoxyribose Sugar
A, T, G, C = Nitrogenous Base
2. Draw a DNA molecule with one strand having the
sequence GATTACA. Label the phosphate, deoxyribose
sugar, bases, hydrogen bonds, 5’ ends, and 3’ ends.
•
•
•
•
•
•
•
•
5’
P- S – G
P – S- A
P- S- T
P – S- T
P-S–A
P – S- C
P- S -A
3’
--------- C – S- P
--------- T- S -P
--------- A- S - P
--------- A- S - P
--------- T- S - P
--------- G -S - P
--------- T – S- P
Hydrogen Bond
3’
5’
3. Why are DNA strands called antiparallel?
• DNA strands are called ‘anti-parallel’
because one strand is built in the 5’ to 3’
direction, and the other is in the 3’ and 5’
direction. They are mirror images of
each other, flipped upside down.
4. Describe the scientific contributions
that each scientist(s) made to the
discovery of DNA:
Chargaff: Chargaff’s rule states that in any DNA
strand, the percentage of A’s and T’s will be
equal, and the percentage of G’s and C’s will be
equal.
Franklin: took the first photo of double helix
using x-ray crystallography
Watson and Crick: discovered the double helix
shape
Sec. 12.2 DNA Replication
1. What is the purpose of a
chromosome?
• The purpose of our 46 chromosomes is to
package a meter of DNA into a
microscopic nucleus.
2. How many chromosomes are in each
human cell?
• 46
3. When is DNA replicated (doubled)?
• In S Phase of the Cell Cycle. We double
our DNA when we need to make new
cells, because every cell needs the same
46 chromosomes.
4. Draw and explain the process of DNA replication,
including all three enzymes involved, the 5’ and 3’
ends of each strand involved, and origins of
replication.
• a. an enzyme, helicase, unwinds the
DNA strands by breaking the hydrogen
bonds. RNA polymerase lays down a
RNA primer as the point of origin.
• b. DNA polymerase builds a new
strand for original strand one. Creating a
continuous strand called the leading
strand
• c. DNA polymerase builds a new
strand for original strand two. Creating a
disconituous strand in the opposite
direction called the lagging strand.
• d. an enzyme, ligase, joins together the
fragments to create a complete strand.
Lagging Strand
Leading Strand
5. Why is one strand built without
interruption while the other is built in
small segments?
• To ensure that the strands are built correctly and
in the correct direction. Lagging strand is built
the opposite way and proofreads along the way
6. What is the finished product of DNA
replication?
• Two identical strands of DNA- each one
with an original strand and copy built by
DNA Polymerase.
Sec. 12.3 Transcription and
Translation
1. Complete
• DNA
mRNA
Proteins
(made of amino acids)
2. Why is an mRNA copy of DNA
necessary?
• The directions for making proteins are
contained in DNA, and the machinery is
the ribosome. DNA can’t leave the
nucleus to get to the ribosome, so the
mRNA acts as a messenger of
information to the ribosome.
3. What are the three major
differences between RNA and DNA?
• 1. RNA is single stranded; DNA is double
stranded
• 2. RNA has ribose sugar; DNA has
deoxyribose sugar
• 3. RNA contains the base uracil (U) in
place of thymine (T), found only in DNA
4. Draw and explain the process of
transcription, including the two steps.
• Step One: RNA
Polymerase (an enzyme)
breaks the DNA strands
apart by breaking the
hydrogen bonds
• Step Two: RNA
Polymerase builds a
single, complimentary
mRNA strand using one
of the DNA strands
• Step Three: The mRNA
leaves the nucleus and
the DNA winds back up
5. If a DNA strand has the sequence
ACATTACGG, what would the mRNA
copy be?
• UGUAAUGCC
6. Where does transcription occur?
• nucleus
7. Draw and explain the three major steps of translation,
including mRNA, ribosome, rRNA, codon, tRNA, anticodon, amino acid, and protein.
• 1. mRNA leaves the nucleus and
binds to a ribosome
• 2. rRNA on the ribosome grabs
the mRNA and begins reading it
three letters at a time (one codon
at a time)
• 3. tRNA with the exact anti-codon
lands on a segment of mRNA and
drops off the amino acid it is
carrying. That segment of mRNA
is pulled through, and another
tRNA lands on an mRNA codon
and drops off its amino acid. The
amino acids link together to form
a protein.
8. If a DNA strand has the sequence TACCCCAAAACT, what
would the mRNA codons and tRNA anti-codons be? What
amino acids are made from this sequence?
• mRNA codons:
AUG GGG UUU UGA
• tRNA anti-codons: UAC CCC AAA ACU
• amino acids (based on mRNA):
Methionine (start), Glycine,
Phenylalanine, Stop
9. Where does translation occur?
• At a ribosome in the cytoplasm
12.4 Mutations
1. What are three causes of DNA
mutations?
• 1. DNA is copied incorrectly by DNA
polymerase in DNA replication
• 2. DNA is copied incorrectly by RNA
polymerase in transcription
• 3. Outside radiation (i.e. UV rays)
damage DNA strands
2. Define substitution, and give an
example of a disease caused by it.
• Substitution is when a letter is put in
place of the letter that is supposed to be
there. Ex.: if DNA is supposed to be
AATG, it is accidentally made as ATTG.
Disease Example: Sickle Cell Anemia
3. Define insertion and deletion and be able to
recognize them. Why are they considered
‘frameshift mutations?’ Why are they more
disruptive to proteins than a substitution?
• Insertion is when an extra letter is put into a DNA
strand, and deletion is when a letter is removed.
Each three letters of DNA makes an mRNA codon,
which codes for a particular amino acid (see section
12.3). By adding or deleting a letter, the DNA code is
off by one letter, making each mRNA codon and
amino acid incorrect. The reading frame of DNA is
shifted one letter, called a ‘frameshift mutation’.
This is very serious because it creates entire
proteins that are wrong, not just one amino acid
that is wrong within a protein.
4. What is the difference between a
gene mutation and a chromosomal
mutation?
• A gene mutation is a change in the DNA
sequence (letters) in a small segment of
DNA. A chromosomal mutation is a
change in an entire chromosome, which
contains millions of letters.
Chromosomal mutations usually result
in death.
5. How can DNA mutations benefit
populations?
• DNA mutations can create physical
characteristics that are beneficial to
individuals. For example, Sickle Cell
Anemia actually protects African
populations from malaria, as the protist
Plasmodium cannot infect a sickle
shaped cell.
Special Topic: Gel
Electrophoresis
1. What two properties determine
which way molecules travel in gel
electrophoresis?
• Electrical charge and size
2. In the gel below, which molecule fragment is
the largest? Smallest? Which molecules are
positively charged? Negatively charged?
• Molecules that are negatively charged go
towards the positive end; those that are
positively charged go to the
• negative end. The smallest molecules
travel the farthest.
• Molecule E is the largest
• Molecule D is the smallest
• Molecule A, C are negatively charged
• Molecule B, D, E are positively charged