Cell Cycle, Chromosomes, Mitosis & Meiosis – Test Study Guide Key
DNA
1. a. What is DNA?
- DNA stores and encodes all of the information in an organism, such as which proteins to make,
and how to make them.
- DNA encodes all of the functions of the cell, including its ability to reproduce
1. b. When an addition, deletion, or substitution happens in DNA strand, then a MUTATION occurs
2. What is the composition of DNA?
- DNA is a double helix made up of two strands twisted together
- The strands each have a sugar and phosphate backbone with nucleotide bases attached in series
along each strand
- DNA is made up of four different nucleotide bases. They are adenosine (A), thymine (T), cytosine
(C), and guanine (G)
3. How is DNA replicated?
Step 1: Helicase enzyme helps the DNA unwind
Step 2: Chain splits breaking Hydrogen bonds
Step 3: DNA Polymerase binds to separated chains
Step 4: New strands are synthesized according to existing DNA – fill in complementary bases
Step 5: DNA strand recoils
End with two double strands of DNA in the double helix shape
RNA AND TRANSCRIPTION
4. What is RNA?
- RNA is a polymer made up of nucleotides
- RNA is single-stranded
- RNA contains the same nucleotides as DNA, with the substitution of uracil (U) for thymine (T)
- 3 types: mRNA is messenger from DNA to protein, tRNA used in translation, and rRNA is
structural element in ribosome
5. What is mRNA?
-
mRNA acts as a messenger, conveying genetic instructions for how to assemble proteins from the
cell’s DNA to its protein-making ribosome
mRNA is assembled using one strand of the cell’s DNA as a template
mRNA contains a copy of one or a few genes (parts), not the entire chromosome.
6. Explain transcription and where it occurs
- RNA is copied from DNA template
- Occurs in nucleus of cell
- Step 1: DNA uncoils for a particular gene(s)
- Step 2: RNA polymerase attaches to DNA and fills in bases
- Step 3: RNA strand starts to form by matching complementary bases (U instead of T)
- Step 4: RNA formed and DNA recoils
PROTEIN SYNTHESIS
7. What is a ribosome?
- A ribosome is an organelle in the cell that assembles the proteins that cell needs to determine its job
8. What is a ribosome’s role in translation?
- A ribosome brings together the mRNA and the tRNA, which assists in the translation process
- During translation, tRNA molecules carrying amino acids are positioned in the ribosome’s two
docking sites
- Afterwards, this machinery can disassemble and be reused many times.
9. What is a codon? What is an anticodon?
- A codon is a sequence of three nucleotides on an mRNA strand that encodes a specific amino acid
- An anticodon is a sequence of three nucleotides that is complementary to the three nucleotides in
the corresponding codon on the mRNA
10. What is tRNA?
- tRNA is a type of RNA that is folded into a specific three-dimensional structure
- It carries and transfers an amino acid to the polypeptide chain that the ribosome is assembling
- One end of the tRNA contains an anticodon, which is specific to one and only one codon
- By binding its anticodon to the complementary mRNA codon, the tRNA acts as an adapter,
bringing into position the correct amino acid that is needed for the polypeptide chain.
11. How does tRNA bind to codons in the mRNA?
- The complementary bases on the codon and anticodon match and are held together by hydrogen bonds
12, How does the code in DNA get converted into a specific amino acid sequence in the polypeptide?
- Nucleotides in the DNA specify the nucleotides in the mRNA
- Nucleotides in the mRNA are read 3 at a time (as codons) by the ribosome
- That codon matches only the anticodon of the tRNA carrying the particular amino acid specified
by the codon
- The ribosome facilitates the binding of the tRNA to the codon.
- The tRNA carries the correct amino acid, which is added to the polypeptide chain in the correct
position.
CHROMOSOMES
13. How many chromosomes are in the human body? 46 or 23 homologous pairs
14. What makes up each chromosome?
- DNA tightly coiled into two sister chromatids connected by the centromere
15. What holds chromatid together? Centromere
16. Sketch & Label all parts of sister chromatids
Cell Reproduction
17. What is asexual reproduction?
- Making new cells by making exact copies of the mother cell. Only one parent.
18. Give 1 examples of asexual reproduction. Binary Fission
19. Which process produces identical new cells --- mitosis, meiosis, or both? Mitosis
Prokaryotic Cell Division
20. Name a prokaryote that reproduces by binary fission. Bacteria
21. Sketch and explain how binary fission occurs in a bacterial cells.
Binary fission is a type of asexual reproduction. The parent bacterial
cell duplicates its genetic material, and divides, each new cell gets a
copy of genetic material and some ribosomes and cytoplasm from
the parent cell.
Cell Cycle
22. From where do new cells arise?
All cells come from other cells.
23. Why does the body constantly make new cells?
- Cells get too large for efficient diffusion of substances across the cell’s interior.
- For unicellular reproduction - ex. fission
- The larger the cell becomes, the more demands the cell places on its DNA.
- For the growth of multi-cellular organisms. (ex. Fertilized egg divides and becomes a multicellular organism)
24. Is cell division the same in all cells? Explain.
No, some cells are exact copies of parent cells – mitosis making diploid cells.
Some cells are divided by meiosis to produce a variety of haploids cells.
25. Why must each new cell get a complete copy of the original cell’s DNA?
Cells need a complete set of DNA to function properly – it is the instruction
manual for the cell.
26. Copying DNA is known as replication.
27. The original cell that divides is called the mother cell, while the two, new identical cells are called
daughter cells.
Cell Cycle
28. Name the 5 phases of the cell cycle.
Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis
29. What is the longest phase of the cell cycle? Interphase
30. Describe what occurs in the G1 stage of interphase.
Growth of the cell, Replication of the organelles
31. When is DNA copied? Synthesis Phase
32. How do the new copies of DNA compare to the original DNA? Exact copies
33.Sketch & label all parts of the cell cycle.
Mitosis
34. In which type of cell does mitosis occur --- prokaryote or eukaryote? Explain why. Eukaryotes –
because prokaryotes do not have a nucleus to divide.
35. Name a type of cell that doesn’t undergo mitosis. Red Blood Cell (made in bone marrow)
36. Name, in order, the four stages of mitosis. Prophase, Metaphase, Anaphase, Telophase
37. What happens during prophase?
a. Chromosomes become visible because they become tightly wound together
b. Nuclear membrane disintegrates
38. What happens to chromosomes during metaphase? They line up along the equator
39. What happens to sister chromatids during anaphase? They are pulled apart
40. What pulls sister chromatids apart during anaphase? The spindle fibers
41. Where are chromatids located during telophase? At opposite poles of the cell
42. What reforms around each set of sister chromatids during telophase? Nuclear membrane
43. What divides during cytokinesis? The cytoplasm and its contents
44. How does the chromosome number of the parent cell compare to that of the 2 daughter cells? How do
the 3 cells compare in size?
- They are the same, both have 46. (in humans)
- The two new daughter cells are much smaller than the original mother cell.
45. If the parent cell has a chromosome number of 2n = 6, what will be the chromosome number of the
daughter cells? 6
46. Label these stages.
Telophase
Anaphase
Interphase
Metaphase
Prophase
47 Eukaryotic cells before and after mitosis are diploid or 2n.
Meiosis
48. How many divisions occur in meiosis? Is this the same as mitosis? Explain.
- There are 2 divisions.
- This is different than mitosis because mitosis only has 1.
49. The original cell that divides by meiosis is diploid or 2n.
50. How many daughter cells can be produced by meiosis? Is this the same as mitosis? Explain.
- 4 very different haploid daughter cells are formed.
- This is different than mitosis, which produces only 2 diploid cells identical to the parent cells.
51. What is the chromosome number of the daughter cells produced by meiosis? How does this compare
to the number of chromosomes in the original cell?
- n or haploid.
- Original cell was 2n or diploid.
52. What are the daughter cells called that are produced by meiosis? Name them.
Gametes – Eggs and Sperm
53. After one division, how many chromosomes are in the cells? 23
54. After the second division, how many chromosomes are in the cells? 23
55. Is meiosis sexual or asexual reproduction? Sexual
56. Are eggs & sperm haploid or diploid? Haploid
57. What process joins the egg & sperm to restore the original chromosome number of the organism?
Sexual reproduction or fertilization
58. When a sperm fertilizes an egg, a new 2n cell forms called the zygote.
59. Homologous chromosomes are pairs of sister chromatids that have the same genes.
60. Meiosis reduces the chromosome number by half, while fertilization restores it.
61. In Meiosis I, what separates? homologous chromosomes
62. In Meiosis II, what separates? Chromatids
63. Name these stages of Meiosis I.
Interphase I
Prophase I
Metaphase I Anaphase I
Telophase I
64. What is a tetrad?
A tetrad is a pair of homologous chromosomes that have lined up together.
Centromere
65. Once tetrads form, what happens to the homologous chromosomes? What is this called?
After the tetrad is formed, they exchange bits and pieces with one another, called crossing over.
66. Crossing-over results in genetic variation in the offspring.
67. What is special about Prophase 1? Metaphase 1?
- Prophase 1 is when crossing over occurs to increase variation
- Metaphase 1 is when chromosomes are sorted independently of each other, which also increases
varition
68. Meiosis results in 4 haploid cells called gametes.
Gametogenesis
69. Gametogenesis that produces sperm cells is called spermatogenesis.
70. Gametogenesis that produces egg cells is called oogenesis.
71. How many haploid cells after oogenesis will become an egg cell? Only one.
Comparing Mitosis & Meiosis
72. Complete the following table comparing mitosis & meiosis.
Mitosis
Meiosis
Number of Divisions
One
Two
Number of Daughter Cells
Two
Four
Genetically Identical
Yes
No
Chromosome Number
46
23
Where Occurs
Somatic (Body) Cells
Sex Cells
Role
Make more identical cells to Make haploid sex cells with
replace dying cells, and
variations in genetic
allow growth of organism
makeup to take place in
sexual reproduction.
73. DNA strand:
mRNA
tRNA
amino acids
CTG GAG AAT
GAC CUC UUA
CUG GAG AAU
aspartic acid leucine
QUIZLET
leucine