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AP2015 Genetics, DNA, Cell Division and Protein Synthesis Review
DNA, and in some cases RNA, is the primary source of heritable information.
a. Genetic information is transmitted from one generation to the next through DNA or RNA.
● Genetic info is stored in and passed along generations via DNA molecules. Rarely RNA may be used (viruses).
● Prokaryotes have circular chromosomes, while eukaryotes multiple linear chromosomes (usually).
● Prokaryotes, viruses and eukaryotes can contain plasmids, (small circular DNA molecules).
● The proof that DNA is the carrier of genetic information involved a number of important historical experiments.
○ i. Contributions of Watson, Crick, Wilkins, and Franklin on the structure of DNA
○ ii. Avery-MacLeod-McCarty experiments
○ iii. Hershey-Chase experiment
● DNA replication ensures continuity of hereditary information.
○ i. Replication is a semiconservative process; one strand = the template for new, complementary strand.
○ ii. Replication requires DNA polymerase plus many other enzymes, occurs bidirectionally, and differs in the
production of the leading and lagging strands.
● Genetic information in retroviruses is a special case and has an alternate flow of information: from RNA to DNA,
made possible by reverse transcriptase, an enzyme that copies the viral RNA genome into DNA.
b.
DNA and RNA molecules have structural similarities and differences that define function.
● Both have three components — sugar, phosphate and a nitrogenous base — which form nucleotide units that are
connected by covalent bonds to form a linear molecule with 3' and 5' ends, with the nitrogenous bases perpendicular
to the sugar-phosphate backbone.
● The basic structural differences include:
○ DNA contains deoxyribose (RNA contains ribose).
○ RNA contains uracil in lieu of thymine in DNA.
○ DNA is usually double stranded, RNA is usually single stranded.
● The two DNA strands in double-stranded DNA are antiparallel in directionality.
● Both DNA and RNA exhibit specific nucleotide base pairing that is conserved through evolution: adenine pairs with
thymine or uracil (A-T or A-U) and cytosine pairs with guanine (C-G).
○ Purines (G and A) have a double ring structure.
○ Pyrimidines (C, T and U) have a single ring structure.
● The sequence of the RNA bases, together with the structure of the RNA molecule, determines RNA function.
● mRNA carries information from the DNA to the ribosome.
● tRNA bind specific amino acids and allow information in the mRNA to be translated to a linear peptide sequence.
● rRNA molecules are functional building blocks of ribosomes.
● The role of RNAi includes regulation of gene expression at the level of mRNA transcription.
c.
Genetic information flows from a sequence of nucleotides in a gene to a sequence of amino acids in a protein.
● The enzyme RNA-polymerase reads the DNA molecule in the 3' to 5' direction and synthesizes complementary
mRNA molecules that determine the order of amino acids in the polypeptide.
● In eukaryotic cells the mRNA transcript undergoes a series of enzyme-regulated modifications.
To demonstrate student understanding of this concept, make sure you can explain:
○ Addition of a poly-A tail
○ Addition of a GTP cap
○ Excision of introns
● Translation of the mRNA occurs in the cytoplasm on the ribosome.
● In prokaryotic organisms, transcription is coupled to translation of the message. 5. Translation involves energy and
many steps, including initiation, elongation and termination. The salient features include:
○ The mRNA interacts with the rRNA of the ribosome to initiate translation at the (start) codon.
○ The sequence of nucleotides on the mRNA is read in triplets called codons.
○ Each codon encodes a specific amino acid, which can be deduced by using a genetic code chart. Many amino
acids have more than one codon.
○ tRNA brings the correct amino acid to the correct place on the mRNA.
○ The amino acid is transferred to the growing peptide chain.
○ The process continues along the mRNA until a “stop” codon is reached.
○ The process terminates by release of the newly synthesized peptide/protein.
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Genetic engineering techniques can manipulate the heritable information of DNA and, in special cases, RNA.
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Electrophoresis
Plasmid-based transformation
Restriction enzyme analysis of DNA
Polymerase Chain Reaction (PCR)
Practice review questions:
1. Explain how the structure of DNA and RNA allow genetic data to be replicated, stored, expressed, and passed along from one
generation to the next?
2. Describe how humans can use biotechnology techniques to modify an organism or to use an organism to produce a biological
molecule such as insulin.
3. Compare the structure of prokaryotic and eukaryotic genetic information storage molecules (chromosomes).
4. Explain how the transmission of DNA from generation to generation reflects the chromosomal nature of inheritance. (in general
terms, square the findings of Mendel with your cellular understanding of meiosis, fertilization, and mitosis)
5. Explain how contributions from each of the following scientists led to an understanding of DNA structure and function:
Griffith
Avery McCarty & McLeod
Hershey & Chase
Erwin Chargaff
Watson, Crick, Franklin, & Wilkins
6. Diagram a molecule of DNA and explain how its features allow for both heredity and protein synthesis.
7. Explain how RNA and DNA differ in structure and function.
8. Explain the role of mRNA, tRNA and rRNA in protein synthesis
9. Explain the relationship between DNA, RNA, Protein, Cells and the Organism.
10. Diagram the process of DNA replication. Explain the roles of all pertinent enzymes.
11. Diagram the process of transcription. Discuss all inputs, processes, and outputs. Explain the roles of any enzymes.
12. Diagram the process of translation. Discuss all inputs, processes, and outputs. Explain the roles of all pertinent enzymes, the
ribosome, and relevant RNA molecules.
13. Compare replication, transcription, and translation among prokaryotes and eukaryotes. Explain the functions of all differences.
Changes in genotype can result in changes in phenotype.
a. Alterations in a DNA sequence can lead to changes in the type or amount of the protein produced and phenotype.
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DNA mutations can be positive, negative or neutral based on the effect or the lack of effect they have on the resulting
nucleic acid or protein and the phenotypes that are conferred by the protein.
b. Errors in DNA replication or DNA repair mechanisms, and external factors, including radiation and reactive chemicals, can
cause random changes, e.g., mutations in the DNA.
c.
Whether or not a mutation is detrimental, beneficial or neutral depends on the environmental context. Mutations are the
primary source of genetic variation.
d. Errors in mitosis or meiosis can result in changes in phenotype.
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Changes in chromosome number often result in new phenotypes, including sterility caused by triploidy and
increased vigor of other polyploids.
Changes in chromosome number often result in human disorders with developmental limitations, including Trisomy
21 (Down syndrome) and XO (Turner syndrome).
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Practice review questions:
1. Explain the relationship of the steps in the cell cycle and the phases of mitosis/meiosis.
2. Compare the effects on an organism of a chromosomal change in mitosis vs. meiosis.
3. Discuss some the causes of mutations.
4. Explain the relationship between mutations, variation, and evolution.
5. Explain the relationship between mutations, and cancer.
6. Describe why mutations can have a positive, negative, or neutral effect on the physiology of the organism.
7. Explain how changes in chromosome number and structure can affect the physiology of the organism.
In eukaryotes, genetic information is passed on through processes that include the cell cycle and mitosis or meiosis plus fertilization.
a. The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cell.
1. Interphase consists of three phases: growth(G1), synthesis of DNA(S), preparation for mitosis(G2).
2. cell cycle directed by “checkpoints”. Internal and external signals provide stop-and-go signs at checkpoints.
b.
Mitosis passes a complete genome from the parent cell to daughter cells.
1.
2.
3.
4.
Mitosis occurs after DNA replication.
Mitosis followed by cytokinesis produces two genetically identical daughter cells.
Mitosis plays a role in growth, repair, and asexual reproduction
Mitosis is a continuous process with observable structural features along the mitotic process. Evidence of student
learning is demonstrated by knowing the order of the processes (replication, alignment, separation).
d. Meiosis, a reduction division, followed by fertilization ensures genetic diversity in sexually reproducing organisms.
1. Meiosis ensures that each gamete receives one complete haploid (1n) set of chromosomes.
2. During meiosis, homologous chromosomes are paired, with one homologue originating from the maternal parent
and the other from the paternal parent.
3. Orientation of the chromosome pairs is random with respect to the cell poles.
4. Separation of the homologous chromosomes ensures that each gamete receives a haploid (1n) set of chromosomes
composed of both maternal and paternal chromosomes.
5. During meiosis, homologous chromatids exchange genetic material via a process called “crossing over,” which
increases genetic variation in the resultant gametes.
6. Fertilization involves the fusion of two gametes, increases genetic variation in populations by providing for new
combinations of genetic information in the zygote, and restores the diploid number of chromosomes.
Practice review questions:
1. Explain where meiosis fits in to the life cycles of sexually reproducing organisms.
2. Explain the similarities and differences among sexual life cycles seen in all organisms. (haplontic, diplontic, alt of gen)
3. Explain the structures and events of all stages of meiosis. (focus on prophase I, metaphase I, and metaphase II)
4. Compare the process of meiosis to the process of mitosis. (create a diagram on blank paper without looking at your book)
5. How do the events of meiosis explain the observations of Gregor Mendel?
6. How do the events of meiosis explain the observations of Thomas Morgan?
7. How can recombination during meiosis be explained?
8. How can recombination during meiosis be utilized to locate genes on chromosomes and establish their relative distances?
9. Compare the process of mitosis in plant-like and animal-like cells.
10. Explain the events of all stages of the cell cycle.
11. Explain how cell division is controlled in cells, using an example like a cyclin-dependent kinase such as MPF.
12. Explain what cancer is and how it develops in an organism
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Practice review questions:
1. State the relationships among chromosomes, DNA, genes, and alleles.
2. Diagram out a sexual life cycle. Include meiosis, mitosis, fertilization, diploid cells, and haploid cells.
3. Why did Mendel use pea plants as his experiments?
4. Distinguish between dominant and recessive; heterozygous and homozygous; phenotype and genotype; wild type and mutant.
5. Define the P, F1, and F2 generations.
6. What is a monohybrid cross, and what are the genotypic and phenotypic ratios expected in the offspring of the cross?
7. How are Punnett squares helpful in following inheritance of single genes?
8. What is a test cross, and why is it useful?
9. How does the law of segregation reflect the events of meiosis?
10. What is a dihybrid cross, and what is the phenotypic ratio expected in the offspring of the cross?
11. How do patterns of inheritance differ for unlinked versus linked pairs of genes?
12. How does the law of independent assortment reflect the events of meiosis?
13. What is the difference between recombinant and parental chromatids, and how do they arise?
14. How do biologists use crossover frequencies to map genes on chromosomes?
15. How do incomplete dominance and codominance increase the number of phenotypes?
16. How can epistasis decrease the number of phenotypes observed in a population?
17. What is the role of the SRY gene in sex determination?
18. Why do males and females express recessive X-linked alleles differently?
19. Why does X inactivation occur in female mammals?
20. How can the environment affect a phenotype?
21. What is a polygenic trait?
22. Explain how each of the following appears to disrupt Mendelian ratios: incomplete dominance, codominance, pleiotropy, epistasis.
23. What is the role of the Y chromosome in human sex determination?
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