Midterm 2 Flashcards
(187 cards)
1
Q
- What is photosynthesis?
A
Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose. It involves using carbon dioxide and water to produce glucose and oxygen.
2
Q
- Which organisms carry out photosynthesis?
A
Organisms that carry out photosynthesis include green plants, algae, and certain bacteria. These organisms contain chlorophyll or similar pigments that enable them to capture sunlight and convert it into energy through photosynthesis.
3
Q
- Why is photosynthesis important?
A
Photosynthesis is essential because it is the primary source of organic matter and energy for nearly all life on Earth. It produces oxygen, which is necessary for the respiration of most organisms, and forms the basis of food chains in ecosystems.
4
Q
- Explain and give examples of the following important terms: autotrophs, photoautotrophs, and heterotrophs
A
Autotrophs:organisms that produce their own food from inorganic substances. Examples include plants, algae, and certain bacteria.
Photoautotrophs: autotrophs that use sunlight to synthesize nutrients through photosynthesis. Examples are green plants, cyanobacteria, and algae.
Heterotrophs: organisms that cannot make their own food and must consume other organisms for energy. Examples include animals, fungi, and many bacteria.
5
Q
- Where does photosynthesis take place in plants?
A
Photosynthesis takes place in the chloroplasts, which are specialized organelles found mainly in the mesophyll cells of plant leaves.
6
Q
- What is the mesophyll?
A
The mesophyll is the inner tissue of a leaf, where most photosynthesis occurs. It contains many chloroplasts that capture light energy and facilitate the production of glucose.
7
Q
- What are stomata and what is their function?
A
Stomata are tiny pores located on the surface of leaves and stems. They regulate the exchange of gases by allowing carbon dioxide to enter the leaf and oxygen and water vapor to exit.
8
Q
- Describe/draw the structure of a chloroplast
A
The chloroplast is a double-membrane-bound organelle
contains structures called thylakoids, arranged in stacks known as grana.
Surrounding the grana is a fluid-filled region called the stroma, which contains enzymes for the Calvin cycle.
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Q
define: thylakoids, grana, and stroma
A
Thylakoids:disk-like structures inside chloroplasts where light-dependent reactions of photosynthesis occur.
Grana: stacks of thylakoids found within chloroplasts.
Stroma: the fluid-filled space surrounding the grana in chloroplasts, where the Calvin cycle takes place to produce glucose.
10
Q
- What equation describes photosynthesis? What gets oxidized there and what gets reduced?
A
6CO_2+6H2O+light energy→C6H12O6+6O2
water (H₂O) is oxidized to produce oxygen (O₂) and
carbon dioxide (CO₂) is reduced to form glucose (C₆H₁₂O₆).
11
Q
- Sketch approximately the photosynthetic absorption spectrum for chlorophyll a, b, and carotenoids
A
Chlorophyll an and b absorb blue and red light; carotenoids absorb blue-green light.
(For a drawing, chlorophyll a and b typically absorb light strongly in the blue and red regions of the spectrum but reflect green, while carotenoids absorb in the blue and reflect yellow to orange.)
12
Q
- Based on q.11 – why the grass is green and red algae and carrots are red?
A
- Grass appears green because chlorophyll reflects green wavelengths of light, even though it absorbs red and blue light.
- Red algae are red because they contain pigments that absorb blue light and reflect red.
- Carrots are red/orange due to carotenoids, which reflect red to orange wavelengths.
13
Q
- What is a function of chlorophyll a and what are the functions of auxiliary pigments?
A
Chlorophyll a plays the primary role in capturing light energy for photosynthesis.
Auxiliary pigments, like chlorophyll b and carotenoids, help capture additional light wavelengths that chlorophyll a cannot absorb effectively, broadening the range of light available for photosynthesis.
14
Q
14a. What are the 2 stages of photosynthesis, and where do they take place?
A
The two stages of photosynthesis are:
1. The light-dependent reactions, which take place in the thylakoid membranes.
2.The Calvin cycle (light-independent reactions), which occurs in the stroma.
15
Q
14b. What happens in these 2 stages? Mention the roles of NADPH and ATP.
A
- In the light-dependent reactions, sunlight is absorbed by chlorophyll, splitting water molecules to produce oxygen, and generating energy-rich molecules, ATP and NADPH.
- In the Calvin cycle, ATP and NADPH are used to convert carbon dioxide into glucose through a series of enzyme-catalyzed reactions.
16
Q
- State the 3 key roles of cell division (i.e. why do we need cell division)
A
- Cell division is essential for growth, allowing organisms to increase in size by producing more cells.
- Cell division is necessary for the repair and replacement of damaged or dead cells.
- Cell division is crucial for reproduction, especially in single-celled organisms, where it enables the production of offspring.
17
Q
Chromosomes
A
Chromosomes: Chromosomes are thread-like structures composed of DNA and proteins, carrying genetic information in the form of genes.
18
Q
Genes
A
Genes: Genes are segments of DNA that contain instructions for the synthesis of proteins, which determine specific traits in an organisms.
19
Q
Chromatin
A
Chromatin: Chromatin is the complex of DNA and protein found in the nucleus of eukaryotic cells, which condenses to form chromosomes during cell division.
20
Q
Somatic cells
A
Somatic cells: Somatic cells are all body cells except for reproductive cells (gametes), and they have a full set of chromosomes.
21
Q
Gametes
A
Gametes: Gametes are reproductive cells (sperm and egg) that contain half the number of chromosomes of somatic cells.
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Q
Sister chromatids
A
Sister chromatids: Sister chromatids are identical copies of a chromosome, connected at the centromere, formed during DNA replication.
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Q
Centromere
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Centromere: The centromere is the region on a chromosome where sister chromatids are attached and where spindle fibers attach during cell division.
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Q
Mitosis
A
Mitosis: Mitosis is the process of cell division that results in two genetically identical daughter cells from a single parent cell
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What are the two main parts of the cell cycle
Interphase and mitotic phase
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The shortest part of the cell cycle consists of 2 phases, which are mitosis and cytokinesis
What happens in each of these phases
- Mitosis: The nucleus divides, distributing duplicated chromosomes evenly between two daughter nuclei.
- Cytokinesis: The cytoplasm divides, resulting in two separate daughter cells.
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The longest part of the cell cycle consists of 3 phases, what are they?
What happens in each of these 3 phases?
- G1 phase: The cell grows, performs normal functions, and prepares for DNA replication.
- S phase: DNA is replicated, resulting in two identical sets of chromosomes.
- G2 phase: The cell continues to grow and prepares for mitosis by producing proteins and organelles needed for cell division.
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5a. Why is it essential that chromosomes (DNA) replicate prior to cell division?
Chromosomes must replicate before cell division to ensure each daughter cell receives an identical set of genetic information, which is crucial for maintaining the organism's functions and traits.
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5b. How many chromosomes are there in human somatic cells?
How many chromosomes are found in human gametes?
46 in somatic cells
23 in gametes
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6a. What is the function of the mitotic spindle?
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The mitotic spindle separates the duplicated chromosomes, ensuring each daughter cell receives an identical set of chromosomes during cell division
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6b. What is the mitotic spindle made of?
The mitotic spindle is made of microtubules, which are protein structures that help move chromosomes.
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6c. What is a kinetochore and what is its function?
A kinetochore is a protein structure on the chromosome where spindle fibers attach during cell division. It helps pull the chromosomes apart to opposite poles of the cell.
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7. What are the stages/phases of mitosis? What key events occur in each phase?
1. Prophase: Chromatin condenses into visible chromosomes; the nuclear envelope begins to break down.
2. Metaphase: Chromosomes align at the cell’s equatorial plane, connected to spindle fibers.
3. Anaphase: Sister chromatids are pulled apart to opposite poles of the cell.
4. Telophase: Chromatids reach opposite poles, nuclear envelopes reform, and chromosomes de-condense.
5. Cytokinesis: The cell’s cytoplasm divides, resulting in two separate daughter cells.
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What is the division of the cytoplasm called? Why is it important?
It is called cytokinesis it’s important because it ensures that each daughter cell has enough cytoplasm and organelles to function independently
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What is the cleavage furrow and how does it form?
The cleavage furrow is an indentation that forms in animal cells during cytokinesis it forms as Actin filaments contract around the center of the cell, pinching it into two separate cells
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What is the cell plate and how does it form?
The cell plate is the structure that forms in plant cells during cytokinesis. It develops from vesicles produced by the Golgi apparatus which align at the centre of the cell to create a new cell wall dividing the cell into two.
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What is the major differences between asexual and sexual reproduction?
Asexual reproduction involves a single parent and produces genetically identical offspring
Sexual reproduction requires two parents and produces genetically unique offspring due to the combination of genetic material
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Heredity
The transmission of treats from parents to offspring
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Variation
Differences in physical traits among individuals within a species
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Genetics
The study of heredity and variation in organisms
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Gene
A unit of heredity that codes for specific protein or trait
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Gametes
Reproductive cells (sperm and egg) that carry half the genetic material of somatic cells
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Chromosomes
Structures made of DNA that carry genetic information
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Locus
The specific location of a gene on a chromosome
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Clone
An organism or cell produced asexually that is genetically identical to the original
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Life cycle
The series of stages and organism goes through from birth to reproduction and death
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Homologous chromosomes
Chromosome pairs that have the same genes at the same loci, but may have different alleles
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Karyotype
The number and visual appearance of chromosomes in a cell
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Sex chromosomes
Chromosomes that determine the biological sex of a organism (X&Y in humans)
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Autosomes
Non-sex chromosomes that carry jeans for traits unrelated to sex
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Haploid cell
A cell with a single set of chromosomes as in gametes
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Diploid cell
A cell with two sets of chromosomes one from each parent
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Ploidy
The number of sets of chromosomes in a cell
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Fertilization
Diffusion of gametes to form a zygote
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Zygote
The cell formed when two gametes unite during fertilization
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Alleles
Variance of a gene that lead to differences in traits
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11. What is the purpose of meiosis?
The purpose of meiosis is to produce gametes with half the number of chromosomes as somatic cells, enabling genetic diversity through recombination and reduction of chromosome number.
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12a. Briefly describe what happens in Meiosis I and Meiosis II.
- Meiosis I: Homologous chromosomes separate, producing two haploid cells with duplicated chromosomes
- Meiosis II: Sister chromatids separate, resulting in four haploid daughter cells, each genetically unique.
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12b. How many daughter cells are there after meiosis I?
What is the ploidy of these cells?
12c. How many daughter cells are there after meiosis II?
What is the ploidy of these cells?
B.2 diploid
C. 4 haploid
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13a. Explain what crossing over is.
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Crossing over is the exchange of genetic material between homologous chromosomes during prophase I of meiosis, resulting in new combinations of alleles
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13b. Why is crossing over important?
Crossing over increases genetic diversity by producing new combinations of genes in offspring.
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13c. What 2 other mechanisms besides crossing over generate genetic variability in sexual reproduction?
1. Independent assortment of chromosomes during meiosis.
2. Random fertilization of gametes.
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Why is genetic variability important?
Genetic variability enhances a populations ability to adapt to environmental changes in increasing survival and reproductive success
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What are the significant differences between mitosis and meiosis?
Mitosis produces two genetically identical, diploid cells involves one division cycle and is used for growth and repair
Meiosis produces for genetically unique haploid cells has two division cycles and is used for sexual reproduction
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Based on char gaff’s rule (and the resulting complementary base pairing) if 10% of DNA bases are a (add nine) how many percent will be C (cytosine) G (guanine) and T (Thymine)
Cytosine: if 10% of the bases are Adenine then Thymine will also be 10%. That leaves 80% of the bases to be equally split between Cytosine and Guanine meaning cytosine will be 40%.
Guanine: since Cytosine is 40% Guanine, which pairs with Cytosine will also be 40%
Thymine: will match the percentage of Adenine so it will be 10%
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2a. Which of the four bases (A, C, G, T) are purines, and which are pyrimidines? How do purines differ from pyrimidines?
Adenine (A) and guanine (G) are purines, which have a two-ring structure. Cytosine (C) and thymine (T) are pyrimidines, which have a single-ring structure. Purines are larger molecules than pyrimidines because of their double-ring structure
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2b. If I have a pyrimidine at a given location on one strand, what would match it from the other strand, purine or pyrimidine?
If there is a pyrimidine on one strand, it will pair with a purine on the other strand, as purines and pyrimidines pair specifically to maintain a consistent width in the DNA helix. Specifically, cytosine (a pyrimidine) pairs with guanine (a purine), and thymine (a pyrimidine) pairs with adenine (a purine).
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3. In the unlabelled graph 16.7, what holds the two strands together?
Hydrogen bonds hold the two strands of DNA together. Specifically, hydrogen bonds form between hydrogen and oxygen atoms or hydrogen and nitrogen atoms within the bases.
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Identify on this unlabelled graph whether a selected base is A, C, G, or T.
To identify whether a given base is A, C, G, or T, you can count the hydrogen bonds: adenine (A) pairs with thymine (T) through two hydrogen bonds, while cytosine (C) pairs with guanine (G) through three hydrogen bonds.
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How can you tell whether a given pair is A-T or C-G?
You can identify a pair as A-T if it has two hydrogen bonds and as C-G if it has three hydrogen bonds.
Hint - In a given pair, which is purine and which is pyrimidine?
In each base pair, one base is a purine (A or G) and the other is a pyrimidine (T or C). This pairing maintains a consistent width in the DNA double helix.
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4a. What 3 models were originally proposed for DNA replication?
1. The conservative model, where the original DNA molecule remains intact, and an entirely new molecule is produced.
2. The semiconservative model, where each of the two daughter molecules has one original strand and one newly synthesized strand.
3. The dispersive model, where each strand of both daughter molecules contain s a mix of old and new DNA.
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4b. In Fig. 16.11, explain what would be this experiment’s expectations – how many bars in the centrifuge tube (corresponding to older (heavier) or lighter (younger) DNA) after the 2nd bacterial division for each of these 3 models, and which of the 3 models was proven correct by this experiment.
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• Conservative model: Expect two bars—one heavy (old) and one light (new).
• Semiconservative model: Expect one intermediate band and one light band.
• Dispersive model: Expect only intermediate-weight DNA.
The semiconservative model was proven correct, as each DNA molecule contains one old strand and one new strand after replication
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5. Describe the chromosome of a bacterium like E. coli.
The chromosome of E. coli is a single, circular DNA molecule. Unlike eukaryotic chromosomes, it is not enclosed in a nucleus but is located in the nucleoid region of the cell.
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6. What type of macromolecules control the organization of chromosomes in a cell (where they are found, how they are folded or unfolded, how they are accessed for obtaining genetic information)?
Proteins, specifically histone proteins, control the organization of chromosomes in a cell. These proteins help package DNA into a compact structure, allowing it to be folded or unfolded as necessary for gene expression and replication.
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7a. Why is chromatin packing necessary?
Chromatin packing is necessary to fit the large amount of DNA into the small space of a cell nucleus. It also helps regulate gene expression by controlling access to specific DNA regions.
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7b. Describe the steps in which chromatin is packed.
Chromatin packing occurs in several levels:
1. DNA wraps around histone proteins to form nucleosomes.
2. Nucleosomes coil to form a 30-nm fiber.
3. The fiber further loops and folds to form higher-order structures, eventually condensing into chromosomes during cell division.
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1. What is a gene?
A gene is a segment of DNA that contains the necessary information to code for a specific protein or functional RNA molecule, playing a key role in determining traits.
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2. What is transcription?
Transcription is the process by which a specific segment of DNA is copied into mRNA, which can then be used to produce a protein.
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3. What is translation?
Translation is the process by which the mRNA sequence is used to build a polypeptide chain (protein), with ribosomes facilitating the assembly of amino acids in the correct order.
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4. What is the central dogma?
The central dogma is the framework describing the flow of genetic information in cells: DNA is transcribed into RNA, which is then translated into protein.
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5a. What are the differences between DNA and RNA?
DNA is double-stranded and contains the sugar deoxyribose, whereas RNA is single-stranded and contains the sugar ribose. Additionally, DNA uses the base thymine (T), while RNA uses uracil (U) in its place.
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5b. What are the 3 types of RNA, and what are their functions?
The three types of RNA are:
1. mRNA (messenger RNA): Carries the genetic code from DNA to ribosomes for protein synthesis.
2. tRNA (transfer RNA): Delivers amino acids to ribosomes during protein synthesis.
3. rRNA (ribosomal RNA): Forms the core of the ribosome's structure and catalyzes protein synthesis.
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Name the enzyme responsible for transcription.
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The enzyme responsible for transcription is RNA polymerase
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7. What is the promoter?
The promoter is a DNA sequence where RNA polymerase binds to initiate transcription. It is typically located upstream of the gene to be transcribed.
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8. Name and describe the 3 stages of transcription.
- Initiation: RNA polymerase binds to the promoter, unwinding the DNA and beginning RNA synthesis.
- Elongation: RNA polymerase moves along the DNA, synthesizing RNA by adding complementary nucleotides.
- Termination: Transcription ends when RNA polymerase reaches a terminator sequence, releasing the newly formed RNA.
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9. How does transcription differ in eukaryotes and prokaryotes?
In eukaryotes, transcription occurs in the nucleus, and the mRNA undergoes processing (splicing, 5' capping, and polyadenylation) before leaving the nucleus. In prokaryotes, transcription occurs in the cytoplasm, and the mRNA does not undergo processing.
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10. Briefly describe the 3 types of eukaryotic mRNA processing. In your answer, explain what exons and introns are.
- 5' Capping: A modified guanine cap is added to the 5' end of the mRNA to protect it and help in ribosome binding.
- Splicing: Introns (non-coding regions) are removed, and exons (coding regions) are joined together to form a continuous coding sequence.
- Polyadenylation: A tail of adenine nucleotides is added to the 3' end to stabilize the mRNA and aid in export from the nucleus.
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11a. Is this mRNA or DNA? (5'-…ACCAUG… -3')
This is mRNA, as it contains uracil (U), which is not found in DNA.
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11b. What was the corresponding DNA code from which our mRNA (5'-…ACCAUG… -3') was transcribed?
The corresponding template DNA strand is 3'-…TGGTAC…-5', which must be read in the 3' to 5' direction to match the mRNA sequence.
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11c. Write a random sequence in mRNA (e.g., 5'-…UCAGGCUAG…-3') and write the template DNA from which this mRNA was transcribed, first in the 3' on the left to 5' on the right, and then flip it to left 5' and 3' on the right.
For the mRNA sequence 5'-…UCAGGCUAG…-3':
• Template DNA in 3'-5' direction: 3'-…AGTCCGATC…-5'
• Flipped to 5'-3' direction: 5'-…CTAGCCTGA…-3'
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12a. What is a codon?
A codon is a sequence of three nucleotide bases in mRNA that codes for a specific amino acid or serves as a start or stop signal in protein synthesis.
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12b. Since we have only 4 different bases to use as “letters” in our code, how long do codons need to be to provide at least one unique codon to each of 20 amino acids?
Codons need to be three bases long to provide 64 unique combinations (4³ = 64), which is enough to code for all 20 amino acids.
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12c. Could we have shorter codons if we had 6 bases instead of 4?
Yes, if there were 6 bases, codons could be two bases long to cover 20 amino acids (6² = 36 combinations), which would still allow for enough unique codons.
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12d. What are “start” and “stop” codons?
Start codons (e.g., AUG) signal the beginning of protein synthesis, while stop codons (e.g., UAA, UAG, UGA) signal the termination of protein synthesis.
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12e. The mRNA base sequence for Lys-Phe-Ser is:
The mRNA codons for Lysine, Phenylalanine, and Serine are AAA, UUU, and UCU, respectively.
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13a. What are these 3 triplets in the mRNA sequence given?
For the mRNA sequence 5'-CACCAUGGGUACAUAACGCGGAGC…-3':
• The three triplets after the start codon (AUG) are AUG, GGU, and ACA.
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13b. Write down the resulting 3-amino acid long polypeptide.
The polypeptide is Met-Gly-Thr.
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13c. What is always the first amino acid in a freshly formed polypeptide?
Methionine (Met) is always the first amino acid before processing.
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13d. Write a random mRNA sequence and see how many, if any, amino acids it forms.
For an mRNA sequence like 5'-AUGUUUGCG-3', it would produce the amino acids Methionine (Met) and Phenylalanine (Phe).
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14. Which positions of codons are more likely to have “silent” substitutions?
Substitutions in the third position of a codon are more likely to be "silent," meaning they do not change the amino acid produced. For example, GCU, GCC, GCA, and GCG all code for Alanine.
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1. How do prokaryotic and eukaryotic cells differ?
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Prokaryotic cells lack a membrane-bound nucleus and organelles, while eukaryotic cells contain a true nucleus and various membrane-bound organelles. Prokaryotes are typically smaller and simpler in structure than eukaryotic cells
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2. In which Domains of life are prokaryotes found?
Prokaryotes are found in the Domains Bacteria and Archaea.
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3. Which Domain has many members that are found in extreme habitats? Describe some of these extreme habitats.
The Domain Archaea contains many members that thrive in extreme habitats, such as high-temperature environments (thermophiles), highly saline environments (halophiles), and acidic or alkaline environments (acidophiles and alkaliphiles).
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4. Are there any prokaryotes that are a) unicellular, b) colonial, c) multicellular?
a) Yes, many prokaryotes are unicellular, existing as single cells.
b) Some prokaryotes form colonies, where cells aggregate and function as a group.
c) True multicellularity, where cells differentiate and specialize, is rare in prokaryotes.
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5. What are the 3 major shapes that prokaryotes can have?
Prokaryotes can have three major shapes:
1 Cocci (spherical)
2 Bacilli (rod-shaped)
3 Spirilla or spirochetes (spiral-shaped)
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Cell wall
• Cell wall: Provides structure, protection, and support to the cell.
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Pili
• Pili: Appendages that allow for the exchange of genetic material between cells during conjugation.
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8. Explain what peptidoglycan is.
Peptidoglycan is a polymer made of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria. It provides structural support and protects the cell.
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9. How do Gram-positive and Gram-negative bacterial cell walls differ?
Gram-positive bacteria have thick peptidoglycan layers in their cell walls, which retain the crystal violet stain used in Gram staining. Gram-negative bacteria have thinner peptidoglycan layers and an outer membrane, making them more resistant to certain antibiotics and not retaining the crystal violet stain.
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10a. Against which type of bacteria would you use Penicillin, and why?
Penicillin is more effective against Gram-positive bacteria because it targets peptidoglycan synthesis, and Gram-positive bacteria have a thicker peptidoglycan layer.
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10b. Why might our mitochondria be affected by Tetracycline and erythromycin, which target prokaryotic ribosomes?
Mitochondria in eukaryotic cells are thought to have evolved from ancient prokaryotes, so their ribosomes are similar to prokaryotic ribosomes. This similarity makes mitochondrial ribosomes vulnerable to antibiotics that target bacterial ribosomes, such as Tetracycline and erythromycin.
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11. What are endospores, when do they form, and why?
Endospores are tough, dormant structures formed by some bacteria in response to unfavorable conditions. They allow the bacteria to survive extreme environments, such as high temperatures and desiccation, and can germinate into active cells when conditions improve.
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12a. What are the three parts of a bacterial flagellum?
The three parts of a bacterial flagellum are:
1 The filament, which extends outside the cell and acts as a propeller.
2 The hook, which connects the filament to the basal body.
3 The basal body, which anchors the flagellum to the cell wall and membrane and acts as a motor.
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12b. What drives the motor of the bacterial flagellum?
The motor of the bacterial flagellum is driven by a flow of protons (H⁺ ions) across the cell membrane, which generates energy for rotation.
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12c. Where have we seen something similar - a molecular motor turned by...? (Hint: lecture units 5 and 6)
This mechanism is similar to ATP synthase, an enzyme that produces ATP by using a proton gradient, found in both cellular respiration and photosynthesis.
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13. Why does the plasma membrane of some bacteria have infoldings?
Some bacteria have infoldings in their plasma membrane to increase surface area for metabolic processes, such as photosynthesis or cellular respiration, which occur along the membrane.
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14. What are plasmids, and why are they important?
Plasmids are small, circular DNA molecules separate from the chromosomal DNA in prokaryotes. They can carry genes that confer advantages, such as antibiotic resistance, and can be exchanged between cells, contributing to genetic diversity.
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15a. Name the process by which prokaryotes reproduce.
Prokaryotes reproduce through binary fission, a process in which a cell divides into two genetically identical daughter cells.
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15b. Why don’t bacteria produce a colony outweighing Earth in 2 days, despite rapid reproduction?
Bacterial growth is limited by factors such as nutrient availability, waste accumulation, competition, and predation, which prevent unlimited reproduction and population growth.
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16a. Why are prokaryotes genetically diverse and able to adapt quickly despite lacking sexual reproduction?
Prokaryotes achieve genetic diversity through mutations and horizontal gene transfer, which allows them to acquire new genes from other organisms, promoting adaptation to changing environments.
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16b. What is horizontal gene transfer, and why is this process significant?
Horizontal gene transfer is the exchange of genetic material between unrelated individuals, allowing prokaryotes to rapidly acquire beneficial traits, such as antibiotic resistance, which enhances their survival.
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16c. Explain the following processes:
• Transformation: The uptake of free DNA from the environment by a prokaryotic cell.
• Transduction: The transfer of DNA from one cell to another via a bacteriophage (a virus that infects bacteria).
• Conjugation: The direct transfer of DNA between two cells, typically through a structure called a pilus.
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Define: autotrophs, photoautotrophs, chemoautotroph and heterotroph
• Autotroph: An organism that produces its own food from inorganic sources.
• Photoautotroph: An autotroph that uses light energy to convert CO₂ into organic compounds.
• Chemoautotroph: An autotroph that obtains energy from chemical reactions involving inorganic substances.
• Heterotroph: An organism that obtains energy by consuming other organisms.
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Define: photoheterotroph, chemoheterotroph, obligate aerobe, obligate anaerobe, and facultative anaerobe
• Photoheterotroph: An organism that uses light for energy but requires organic compounds as a carbon source.
• Chemoheterotroph: An organism that derives energy and carbon from organic compounds.
• Obligate aerobe: Requires oxygen to survive.
• Obligate anaerobe: Cannot survive in the presence of oxygen.
• Facultative anaerobe: Can survive with or without oxygen.
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18a. Why do living organisms require nitrogen?
Nitrogen is essential for building amino acids, proteins, nucleic acids, and other vital biomolecules in living organisms.
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18b. What is nitrogen fixation, i.e., what do nitrogen-fixing prokaryotes do?
Nitrogen fixation is the process by which certain prokaryotes convert atmospheric nitrogen (N₂) into ammonia (NH₃), a form that can be utilized by plants and other organisms for building essential compounds like amino acids and nucleotides.
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18c. Give an example of a nitrogen-fixing prokaryote.
An example of a nitrogen-fixing prokaryote is Rhizobium, a bacterium that forms symbiotic relationships with legume plants and converts nitrogen gas into ammonia.
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18d. Why are photosynthesis and nitrogen fixation carried out in separate cells in Anabaena?
In Anabaena, photosynthesis and nitrogen fixation are separated to prevent oxygen, a byproduct of photosynthesis, from interfering with the nitrogenase enzyme, which is oxygen-sensitive and required for nitrogen fixation.
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18e. What are heterocysts?
Heterocysts are specialized cells found in certain cyanobacteria, such as Anabaena, that provide an anaerobic environment for nitrogen fixation, protecting the nitrogenase enzyme from oxygen.
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18f. How are some cyanobacteria able to fix nitrogen without being colonial or having heterocysts?
Some cyanobacteria fix nitrogen by carrying out nitrogen fixation at night when photosynthesis does not produce oxygen, thus avoiding interference with the nitrogenase enzyme.
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19. What are biofilms, and how does metabolic cooperation work in them?
Biofilms are communities of microorganisms that adhere to a surface and work together, often encased in a protective matrix. Metabolic cooperation allows different species within the biofilm to perform complementary metabolic processes, enhancing nutrient availability and protection from external threats.
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20. Name two reasons why cyanobacteria are important to other organisms in the ecosystems they live in.
1 Cyanobacteria produce oxygen through photosynthesis, which supports aerobic life forms.
2 Cyanobacteria contribute to nitrogen fixation, enriching ecosystems with bioavailable nitrogen essential for plant and microbial growth.
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21. Name and explain three crucial roles of prokaryotes in the biosphere.
1 Decomposition: Prokaryotes break down organic matter, recycling nutrients back into ecosystems.
2 Nitrogen Fixation: Prokaryotes convert atmospheric nitrogen into forms that can be used by plants and other organisms.
3 Photosynthesis: Photosynthetic prokaryotes, like cyanobacteria, produce oxygen and serve as primary producers in aquatic ecosystems.
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22. Describe the three types of symbiosis and give an example associated with humans for each.
1 Mutualism: Both organisms benefit. Example: Gut bacteria in humans help digest food and produce vitamins.
2 Commensalism: One organism benefits without affecting the other. Example: Certain skin bacteria benefit by living on human skin without harming or helping us.
3 Parasitism: One organism benefits at the expense of the other. Example: Pathogenic bacteria, like Mycobacterium tuberculosis, cause disease in humans.
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23. Define the term pathogen.
A pathogen is a microorganism, such as a bacterium, virus, or fungus, that causes disease in its host.
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24. Name two main ways in which bacteria can harm our bodies, and what types of toxins are used in each case.
1 Exotoxins: These are toxins secreted by bacteria that can damage host tissues or disrupt normal cellular functions. Example: Clostridium botulinum produces botulinum toxin.
2 Endotoxins: These toxins are part of the bacterial cell wall and are released when the cell dies, causing inflammation and fever. Example: Escherichia coli can release endotoxins when its outer membrane breaks down.
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27. What are some examples of practical/beneficial uses of prokaryotes in research and technology?
Prokaryotes are used in various applications, including:
• Bioremediation: Certain bacteria can break down pollutants, such as oil spills or heavy metals.
• Genetic Engineering: Bacteria are used in research to produce pharmaceuticals, like insulin.
• Agriculture: Nitrogen-fixing bacteria improve soil fertility, benefiting crop production.
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1. When did microbial (prokaryotic) cells first appear in the fossil record?
Microbial (prokaryotic) cells first appeared in the fossil record approximately 3.5 billion years ago.
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2. What organisms are believed to be responsible for the oxygenation of Earth?
Cyanobacteria, which perform photosynthesis and release oxygen as a byproduct, are believed to be responsible for the oxygenation of Earth, a process that significantly increased atmospheric oxygen levels around 2.4 billion years ago (the Great Oxygenation Event).
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3. When did eukaryotes first appear?
Eukaryotes are believed to have first appeared approximately 1.8 billion years ago.
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4. What cellular structures do eukaryotes have that prokaryotes do not have?
1. A membrane-bound nucleus that contains the cell’s DNA.
2. Membrane-bound organelles, such as mitochondria, chloroplasts (in plant cells), and the endoplasmic reticulum.
3. A cytoskeleton made of microtubules and microfilaments for support and intracellular transport.
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5. Recent data provides evidence that eukaryotes emerged from which group of prokaryotes?
Recent data suggests that eukaryotes emerged from a group of prokaryotes called archaea, specifically from a subgroup known as Asgard archaea.
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6. Explain endosymbiosis and endosymbiont
• Endosymbiosis: Endosymbiosis is a symbiotic relationship in which one organism lives inside the cells of another organism. This theory suggests that certain organelles in eukaryotic cells, such as mitochondria and plastids, originated from free-living bacteria that were engulfed by a host cell.
• Endosymbiont: An endosymbiont is an organism that lives within the body or cells of another organism in a mutually beneficial relationship
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Explain: host, mitochondria, and plastid
.
• Host: The host is the larger organism that houses the endosymbiont within its cells, benefiting from the endosymbiont’s functions, such as energy production.
• Mitochondria: Mitochondria are organelles in eukaryotic cells responsible for producing ATP through cellular respiration. They are thought to have originated from aerobic bacteria engulfed by an ancestral eukaryotic cell.
• Plastid: Plastids are a group of organelles, including chloroplasts, found in plants and algae. They are responsible for photosynthesis and are believed to have originated from photosynthetic bacteria engulfed by a eukaryotic cell.
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7. The bacterial ancestor of the mitochondrion probably entered the host cell as...
The bacterial ancestor of the mitochondrion probably entered the host cell as an ingested prey or as a parasite, eventually forming a mutually beneficial relationship with the host cell.
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8. Why do scientists believe mitochondria evolved before plastids (chloroplasts)?
Scientists believe mitochondria evolved before plastids because all eukaryotic cells contain mitochondria or their remnants, while only plants and some protists contain plastids. This suggests that the endosymbiotic event that led to mitochondria occurred earlier in evolutionary history.
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9. Explain the hypothesis for the origin of eukaryotes through serial endosymbiosis.
T
he hypothesis for the origin of eukaryotes through serial endosymbiosis suggests that the ancestral eukaryotic cell formed through a series of symbiotic events. Initially, an archaeal host cell engulfed an aerobic bacterium, leading to the formation of mitochondria. Later, in some lineages, this eukaryotic cell engulfed a photosynthetic cyanobacterium, giving rise to plastids in plants and algae. This stepwise process of engulfing and retaining beneficial organisms eventually led to the diversity of eukaryotic cells seen today.
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10. What pieces of evidence support the endosymbiotic origin of mitochondria and plastids?
1 Double Membranes: Mitochondria and plastids have double membranes, consistent with the engulfing process.
2 DNA Similarity: Both organelles contain their own circular DNA, similar to bacterial genomes.
3 Ribosomes: Mitochondria and plastids have ribosomes similar in size and structure to bacterial ribosomes, not eukaryotic ribosomes.
4 Binary Fission: Mitochondria and plastids replicate independently of the cell through a process similar to binary fission, like bacteria.
5 Genetic Similarity to Bacteria: Genetic analyses reveal that mitochondrial DNA is closely related to that of certain aerobic bacteria, while plastid DNA is similar to cyanobacteria.
6 Antibiotic Sensitivity: Mitochondria and plastids are sensitive to certain antibiotics that inhibit bacterial protein synthesis but do not affect eukaryotic cells.
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1. What are protists?
Protists are a diverse group of eukaryotic organisms that are not plants, animals, or fungi. They are mostly unicellular, although some are multicellular or colonial, and they inhabit various environments, especially aquatic ones.
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2. What type of habitat are protists found in?
Protists are typically found in moist or aquatic habitats, such as freshwater, marine environments, and damp soil.
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3. What are the 4 ways in which protists can get their nutrition, and give one protist example for each?
1 Photoautotrophs: These protists use sunlight to produce energy, like Euglena.
2 Heterotrophs: These protists obtain nutrients by ingesting other organisms, like Amoeba.
3 Mixotrophs: These protists can use both photosynthesis and ingestion, depending on the availability of light and food, like Dinoflagellates.
4 Parasitism: These protists obtain nutrients from a host organism, often causing harm, like Plasmodium (which causes malaria).
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4. Name 4 of the supergroups of eukaryotes.
The four supergroups of eukaryotes are:
1 Excavata
2 SAR clade
3 Archaeplastida
4 Unikonta
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5. What supergroup do Diplomonads, Parabasalids, and Euglenozoans belong to, and what are the 3 diagnostic features of the members of this supergroup?
Diplomonads, Parabasalids, and Euglenozoans belong to the supergroup Excavata. The diagnostic features of Excavata members include:
1 A unique cytoskeletal structure.
2 An excavated feeding groove on one side of the cell body.
3 Modified mitochondria or unique flagella.
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6. What two general characteristics do Diplomonads and Parabasalids have?
Diplomonads and Parabasalids both have reduced or modified mitochondria and are often anaerobic, living in low-oxygen environments.
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7. What disease is caused by a diplomonad Giardia intestinalis, and how can we get infected by it?
The diplomonad Giardia intestinalis causes giardiasis, a diarrheal disease. Humans can get infected by ingesting contaminated water, food, or through direct contact with infected individuals.
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8. Parabasalid Trichomonas vaginalis has a unique (“barbed-wire”-like) structure. What is it called, and how does this Parabasalid use it?
Trichomonas vaginalis has an undulating membrane, a structure that helps it move through mucus-lined surfaces in the human reproductive tract.
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9. What unusual characteristic do Euglenozoans have?
Euglenozoans have a crystalline or spiral rod inside their flagella, which is a distinguishing feature of this group.
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10. What gave the name Kinetoplastid?
The name Kinetoplastid comes from the presence of a kinetoplast, a unique, large mass of mitochondrial DNA located near the cell's flagellum.
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11. What disease is caused by a Kinetoplastid Trypanosoma species?
A Kinetoplastid Trypanosoma species causes African sleeping sickness.
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12. How is this organism spread?
Trypanosoma is spread by the bite of an infected tsetse fly.
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13a. How do trypanosomes defend themselves against our immune system?
Trypanosomes evade the immune system by frequently changing the proteins on their cell surface, making it difficult for the immune system to recognize and attack them effectively.
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13b. Name the process in which they acquired the genes they use for this defense.
Trypanosomes acquired these genes through horizontal gene transfer.
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14a. Describe the structure of Euglena. What habitat is Euglena found in?
Euglena has a flexible outer membrane called a pellicle, a flagellum for movement, chloroplasts for photosynthesis, and an eye spot. Euglena is commonly found in freshwater environments.
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14b. Why does Euglena need an eyespot?
The eyespot in Euglena detects light, allowing it to move towards light sources for photosynthesis.
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15. The SAR clade includes these 3 subgroups. Indicate one or more characteristics for each subgroup:
1 Stramenopiles: Known for their hairy and smooth flagella, includes diatoms and brown algae.
2 Alveolates: Characterized by membrane-bound sacs (alveoli) under their plasma membranes, includes dinoflagellates and ciliates.
3 Rhizarians: Often have intricate mineral skeletons and are mostly amoeboid, including foraminiferans and radiolarians.
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16. Describe/draw the structure of brown algae (see Figure 28.11).
Brown algae typically have a holdfast to anchor them, a stipe that acts like a stem, and blades that resemble leaves, aiding in photosynthesis. (Please refer to Figure 28.11 for a visual structure in your materials.)
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17. Holdfast is not a true root because it does not perform one of the major functions of a true root. What function is that, and why does the holdfast not need or cannot perform this function?
A holdfast is not involved in the absorption of water and nutrients as a true root would. Brown algae are surrounded by water, allowing them to absorb nutrients directly from their surroundings without the need for root-like absorption.
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18. What type of life cycle does the brown alga Laminaria have?
Laminaria has an alternation of generations life cycle, involving both haploid and diploid stages.
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19. Draw and describe the life cycle of Laminaria.
(A drawing would illustrate the alternation of generations, with a diploid sporophyte producing haploid spores that grow into gametophytes, which then produce gametes that combine to form a new diploid sporophyte. Please refer to your materials for specific details.)
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20. The diagnostic feature of the Alveolates is the presence of...
The diagnostic feature of Alveolates is the presence of alveoli, small membrane-bound sacs just under the cell membrane.
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21a. Name the protist that causes malaria.
The protist that causes malaria is Plasmodium.
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21b. Where geographically is malaria found?
Malaria is primarily found in tropical and subtropical regions, especially in sub-Saharan Africa, South Asia, and parts of Central and South America.
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22. What are the two hosts of the protist that causes malaria?
The two hosts of Plasmodium (the malaria-causing protist) are humans and the Anopheles mosquito.
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23. What is the function of an apical complex?
The apical complex allows certain parasitic protists, such as Plasmodium, to penetrate and infect host cells.
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24. Draw the two-host life cycle of the protist that causes malaria and describe what happens in each stage.
(A drawing would show the mosquito transmitting Plasmodium sporozoites into the human bloodstream, where they infect liver cells, multiply, and then invade red blood cells. Inside red blood cells, they replicate and cause symptoms of malaria before being picked up again by another mosquito. Refer to your textbook for visual aid.)
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25. How has Plasmodium falciparum been able to evade the host immune response?
Plasmodium falciparum evades the immune response by frequently changing its surface proteins, which helps it avoid recognition by the host’s immune system.
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26. What did the apicoplast evolve from, what are its functions, and why might having it help us develop a drug that targets malaria without affecting humans?
The apicoplast evolved from an ancient plastid and is involved in metabolic processes that are essential for the survival of the parasite. Since humans lack an apicoplast, targeting it with drugs could harm the parasite without affecting human cells, offering a pathway for anti-malarial drug development.
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27. What feature gave the name to the Supergroup Unikonta?
The name Unikonta refers to the presence of a single flagellum in certain stages of the life cycle or the use of a single basal body, as seen in some members of this group.
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28. List the characteristics of Amoebozoans.
Amoebozoans are characterized by their lobe- or tube-shaped pseudopodia used for movement and feeding. They are mostly heterotrophic and found in various habitats, including soil, freshwater, and marine environments.
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29. How do tubulinids feed themselves?
Tubulinids feed by phagocytosis, engulfing food particles using their pseudopodia and digesting them within food vacuoles.
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30. What disease does Entamoeba histolytica cause?
Entamoeba histolytica causes amoebic dysentery, a serious intestinal illness.
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31. Draw and describe the life cycle of a plasmodial slime mold.
*(A drawing would show a multinucleate feeding stage, where the slime mold grows and consumes food through phagocytosis
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Capsule
• Capsule: A protective outer layer that aids in adhesion to surfaces and protects against desiccation and phagocytosis.
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Fimbriae
• Fimbriae: Hair-like structures that help prokaryotes attach to surfaces and other cells.
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Plasma membrane
• Plasma membrane: Regulates the movement of substances into and out of the cell.
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Ribosomes
• Ribosomes: Sites of protein synthesis.
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Flagella
• Flagella: Enable movement by rotating, allowing the cell to swim through liquids.
