Download DNA, Mitosis, and Protein Synthesis Exam Review Guide

DNA, Mitosis, and Protein Synthesis Exam Review Guide
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Part 1: DNA Structure
1.
How does the genetic information coded in the DNA of a muscle cell in your arm compare to the genetic
information in the DNA of a cell in your brain?
They are exactly identical. Because of mitosis makes genetically identical daughter cells, and all of your cells are made
through mitosis, all the cells in your body have the exact same DNA in them.
2.
What happens to allow your brain cells to take a different shape and function compared to your arm
cells?
Different genes are turned on and off so they make different proteins. These different proteins give them different shape
and different jobs.
3.
Draw a nucleotide and label the three parts
4.
Draw a DNA double helix and label the sugar phosphate backbone and
the bases.
5.
For the sequence of DNA bases below, write the complementary DNA
bases below each one.
TACTGTAAAGGCTATATGCCGAAT
ATGACATTTCCGATATACGGCTTA
6.
If there are 700 Guanine nucleotides and 300 Adenine nucleotides in a DNA molecule, how many Cytosine and
Thymine nucleotides are there?
a. C’s ____700______
b. T’s ____300______
Part 2: DNA Replication
7.
Describe the process of DNA replication.
1.
2.
3.
4.
5.
Helicase unzips the DNA
Free nucleotides base pair (hydrogen bond) with the original strand
DNA polymerase bonds the sugar phosphate backbone
An enzyme rewinds the double helix
Two double helices, each containing half of the old one
8.
What is the end result of DNA replication? Describe the presence of “new” DNA and “old” in the
resulting strands.
Two identical strands of DNA – they carry the exact same genetic information. Each contains half “old” DNA
and half “new” DNA.
9.
What would happen to DNA replication if there was no DNA polymerase?
The new bases would be able to hydrogen bond, but the sugar phosphate backbone would not be bound
together and they would not stay around and make a cohesive piece of DNA
10.
What would happen to DNA replication if there was no free A nucleotides?
There would be a lot of gaps in the new DNA strand, since there would be no As. DNA polymerase probably
wouldn’t be able to work very well because there wouldn’t be enough of a sugar/phosphate backbone to bind
together. Replication would not able to occur.
11.
What would happen to DNA replication if there was no helicase?
It would not be able to get started because the two strands of DNA would not unzip.
12.
The bonds between the nucleotides are strong
covalent
bonds. The bonds between the
bases are weak
hydrogen
bonds. What affect does this have on the process of DNA replication?
The weak hydrogen bonds make it easy to unwind the strands of DNA, but the strong covalent bonds make
sure that the unwound strands lines of DNA stay together. If the covalent bonds were weak, the DNA would
break all apart and it would get scrambled instead of replicated. If the hydrogen bonds were strong, it would
take a lot of energy to unzip DNA and probably slow the process down.
Part 3: Mitosis
Chromosomes
1. Why do cells have chromosomes?
To store and protect and condense DNA
2. Chromosomes are made out of DNA wrapped around histone proteins. Label both in the picture
below.
DNA
histone protein
3. During what phases of the cell cycle are chromosomes obvious?
telophase
metaphase, anaphase, and
4. How many chromosomes are present in a human body cell?
46
Phases of the cell cycle
5. What is the end result of mitosis?
Two genetically identical daughter cells
6. Why do cells need mitosis? Growth and repair
7. What happens if there is not enough cell division?
Organisms will not be able to repair injuries.
Young organisms will not be able to grow and develop. Organisms will nto be able to replace dead cells
8. What happens if there is too much cell division?
cancer
Match the description of the even with the phase of mitosis it is in.
Event
__ C ___ 9. The chromosomes move until they form two groups near the
poles of the spindle
Phase
a. Prophase
b. Metaphase
__ A ___10. The chromosomes become visible. The centrosomes take
up position on opposite sides of the nucleus.
___ D __11. A nuclear envelope re-forms around each cluster of
chromosomes.
c. Anaphase
d. Telophase
___ B __12. The chromosomes line up across the center of the cell.
13. Label the pictures below with the appropriate phase of mitosis and structures of the cell.
Prophase
Metaphase
Spindle fiber
centrosome
Chromosome
/centromere
Interphase
Nucleus membrane
Anaphase
Cell membrane
centriole
Telophase/Cytokinesis
Interphase
Sister chromatids
Cell membrane
DNA
14. If a cell has 14 chromosomes in interphase (S1), how many will it have in metaphase?
28
15. If a cell has 36 chromosomes in metaphase, how many will it have in interphase (S1)?
18
16. If a cell has 8 chromosomes before the DNA replicates, how many will it have after the DNA replicates?
16
Part 4: RNA and Protein Synthesis
A brief reminder: RNA Synthesis Most of the work of making RNA takes place during transcription. In
transcription, segments of DNA serve as templates to produce complementary RNA molecules. In prokaryotes,
RNA synthesis and protein synthesis takes place in the cytoplasm. In eukaryotes, RNA is produced in the cell’s
nucleus and then moves to the cytoplasm to play a role in the production of protein. The following focuses on
transcription in eukaryotic cells.
▶ The enzyme RNA polymerase binds to DNA during transcription and separates the DNA strands. It then
uses one strand of DNA as a template from which to assemble nucleotides into a complementary
strand of RNA.
▶ RNA polymerase binds only to promoters, regions of DNA that have specific base sequences. Promoters
are signals to the DNA molecule that show RNA polymerase exactly where to begin making RNA.
Similar signals cause transcription to stop when a new RNA molecule is completed.
▶ RNA may be “edited” before it is used. Portions that are cut out and discarded are called introns. The
remaining pieces, known as exons, are then spliced back together to form the final mRNA.
1. Complete the table to contrast the structures of DNA and RNA.
DNA
Sugar
Deoxyribose
Number of Strands
2
Bases
A, T, G, C
RNA
Ribose
1
A, U, G, C
2. In eukaryotes, RNA is formed in the
nucleus
and then travels to the cytoplasm
3. The
RNA polymerase
enzyme binds to DNA during transcription.
.
Part 5: Ribosomes and Protein Synthesis
The Genetic Code A specific sequence of bases in DNA carries the directions for forming a polypeptide, a chain of
amino acids. The types and order of amino acids in a polypeptide determine the properties of the protein. The sequence
of bases in mRNA is the genetic code. The four bases, A, C, G, and U, act as “letters.”
▶ The code is read three “letters” at a time, so that each “word” is three bases long and corresponds to a single
amino acid. Each three-letter “word” in mRNA is known as a codon.
▶ Some codons serve as “start” and “stop” signals for protein synthesis.
▶ The central dogma of molecular biology is that information is transferred from DNA to RNA to protein.
Translation Ribosomes use the sequence of codons in mRNA to assemble amino acids into polypeptide chains. The
process of decoding of an mRNA message into a protein is translation.
▶ Messenger RNA is transcribed in the nucleus and then enters the cytoplasm.
▶ On the ribosome, translation begins at the start codon. Each codon attracts an anticodon, the complementary
sequence of bases on tRNA.
▶ Each tRNA carries one kind of amino acid. The match between the codon and anticodon ensures that the
correct amino acid is added to the growing chain.
▶ The amino acids bond together, each in turn. The ribosome moves along the mRNA, exposing codons that
attract still more tRNAs with their attached amino acids.
▶ The process concludes when a “stop code” is reached. The newly formed polypeptide and the mRNA molecule
are released from the ribosome.
Use the diagram to answer Questions 8–10.
1. What is the anticodon for leucine?
2. What is the codon for leucine?
GAC
CUG
3. List the amino acids in the order they would appear
in the polypeptide coded for by this mRNA.
Methionine, phenylalanine, lysine, leucine
4. What is the difference between transcription and
translation?
RNA is produced from DNA templates during transcription. In
translation, that RNA is read to form polypeptide chains. In an eukaryotic cell,
transcription goes on in the nucleus and translation is carried out by the ribosomes
5. Complete the table to describe the steps in protein synthesis.
Step
Description
Beginning of translation
Translation begins when a ribosome attaches to an mRNA molecule to a
“start” codon. tRNA molecules carry amino acids to the mRNA, where the
anticodon matches the codon and ensures the placement of the correct
amino acid
Assembly of polypeptide
Amino acids join one at a time onto the growing chain, and a tRNA floats
away after it releases its amino acid. The ribosome moves along the
mRNA, binding a new tRNA molecule and the amino acid it carries.
Completing the polypeptide
The process continues until a “stop” codon is reached, the polypeptide is
complete, and the mRNA is released from the ribosome.
6. The central dogma of molecular biology is that information is transferred from
A. RNA to protein to DNA.
B. DNA to protein to RNA.
C. protein to DNA to RNA.
D. DNA to RNA to protein.
7. An exception to the central dogma is
A. the infection of a virus by a bacteriophage.
B. the ability of some viruses to transfer information from RNA to DNA.
C. the expression of different genes during different stages of development.
D. the translation of the codon into the anticodon of tRNA.
8. All organisms are mostly the same in
A. the proteins they make on their ribosomes.
B. how their proteins catalyze chemical reactions.
C. the size of their genes.
D. the molecular biology of their genes.
9. Whether the organism is a pea plant or a human being, the information in the DNA of the cell’s nucleus directs
synthesis of proteins in the cytoplasm. Why, then, are pea plants and human beings so different?
They contain different sequences of DNA, which directs the synthesis of different
proteins. Those proteins form different structures and functions, making pea plant cells very
different from human cells.
Part 6: Mutations
Types of Mutations Mutations are heritable changes in genetic information. There are
two categories of mutations: gene mutations and chromosomal mutations.
▶ Gene mutations produce changes in a single gene. Point mutations involve only one or a
few nucleotides. Substitutions, insertions, and deletions are all types of point mutations.
• In a substitution, one base is changed to a different base, which may affect only a single
amino acid and have no effect at all.
• In insertions and deletions, one base is inserted or removed from the DNA sequence.
Insertions and deletions are called frameshift mutations because they shift the “reading
frame” of the genetic message. Frameshift mutations can change every amino acid that
follows the point of mutation and can have dramatic effects on the organism.
▶ Chromosomal mutations produce changes in the number or structure of chromosomes.
They include deletions, duplications, inversions, and translocations.
• Deletion involves the loss of all or part of a chromosome.
• Duplication produces an extra copy of all or part of a chromosome.
• Inversion reverses the direction of parts of a chromosome.
• Translocation occurs when part of one chromosome breaks off and attaches to another.
Effects of Mutations Genetic material can be altered by natural events or by artificial means. Errors can be
made during replication. Environmental conditions may increase the rate of mutation. Mutagens are chemical
or physical agents in the environment that cause mutations.
The effects of mutations on genes vary widely:
▶ Some mutations have little or no effect.
▶ Some mutations produce beneficial variations. One example is polyploidy in plants, in which an
organism has extra sets of chromosomes. Polyploid plants are often larger and stronger than
diploid plants. Mutations can also produce proteins with new or altered functions that can be
useful to organisms in different or changing environments.
▶ Some mutations negatively disrupt gene function or dramatically change protein structure. Genetic
disorders such as sickle cell disease can result.
Types of Mutations
1. Complete the table to describe the processes and outcomes of the different types of gene
(point) mutations.
Type
Description
Outcome
Substitution
One base is changed to a different
Usually affects no more than a single
base
amino acid, and sometime has no
effect at all
Insertion
An extra base is inserted into the
DNA sequence
The effects can be dramatic. The
groupings of bases shift in every
codon that follows the mutation.
Deletion
A base is removed from the DNA
sequence
The effects can be dramatic. The
groupings of bases shift in every
codon that follows the mutation.
2. A possible mutagen is
A. an anticodon.
B. translocation.
C. hemoglobin.
D. ultraviolet light.
3. What happens when cells cannot repair the damage caused by a mutagen?
A. The DNA base sequence changes permanently.
B. The DNA base sequence is not affected.
C. The organism is not affected.
D. The organism is affected temporarily.
4. Which of the following most accurately summarizes the effects of mutations on living things?
A. Most mutations are harmful, but some have little effect.
B. Many mutations have little or no effect, but some can be harmful or beneficial.
C. Most mutations are beneficial and a few are harmful.
D. About half of mutations are beneficial and half are harmful.
5. Cancer is the product of a mutation that
A. causes the uncontrolled growth of cells.
B. changes the structure of hemoglobin in the blood.
C. brings about stunted growth and severe pain.
D. causes a translocation in a pair of chromosomes.
6. A gene that codes for one of the polypeptide chains of the blood protein hemoglobin lies on chromosome 11 in
humans. A substitution mutation in that gene causes the amino acid valine to be incorporated into hemoglobin in a
place where glutamic acid would normally lie. The result is sickle cell disease. Explain how a change in a single base
in DNA can bring about such a serious disorder.
A single DNA base-pair change in a gene can create an incorrect codon in the mRNA
molecule made from this DNA. When the incorrect codon is “read” on the ribosome, the wrong
amino acid (in this case valine rather than glutamic acid) is place into the polypeptide. With
the wrong amino acid sequence, the protein does not form or function properly.