Introduction to Cells

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Questions and Answers

What is the central dogma of molecular biology, and how does it illustrate the unity of life at the cellular level?

The central dogma states that genetic information flows from DNA to RNA to protein. This is a universal process shared by all living cells.

Explain how the existence of extremophiles within the Archaea domain challenges our understanding of the conditions necessary for life.

Extremophiles thrive in extreme conditions such as high temperatures, salinity, or absence of oxygen, demonstrating that life can exist in environments previously thought uninhabitable.

Describe the evolutionary significance of the endosymbiotic theory in the context of eukaryotic cell development.

The endosymbiotic theory posits that mitochondria and chloroplasts in eukaryotic cells originated as symbiotic bacteria. This explains their double membranes and independent genetic material.

Contrast the cell wall composition of Bacteria and Archaea and explain why this difference is significant.

<p>Bacterial cell walls contain peptidoglycan, which is absent in Archaea. This difference is significant because it reflects distinct evolutionary pathways and adaptations to different environments.</p> Signup and view all the answers

Explain how the classification of 'Protista' as a non-monophyletic group impacts our understanding of eukaryotic evolution.

<p>The non-monophyletic nature of 'Protista' indicates that its members do not share a single common ancestor, suggesting multiple independent origins of certain eukaryotic traits.</p> Signup and view all the answers

Describe how the structural diversity of nerve cells (neurons) reflects their specialized function in transmitting electrical signals.

<p>Neurons have a long axon for signal transmission and dendrites for receiving signals. This structure facilitates rapid and directed communication.</p> Signup and view all the answers

Explain the concept of an 'autocatalytic process' in the context of living cells, referencing the roles of DNA, RNA, and proteins.

<p>An autocatalytic process is self-replicating. DNA and RNA encode information for protein synthesis, while proteins catalyze the replication of DNA and RNA, creating a self-sustaining system.</p> Signup and view all the answers

How does the presence of introns in genes differ between Bacteria, Archaea, and Eukarya, and what implications does this have for genome evolution?

<p>Introns are very rare in Bacteria, present in some genes in Archaea, and common in Eukarya. This suggests increasing complexity in gene regulation and genome evolution from prokaryotes to eukaryotes.</p> Signup and view all the answers

Describe how the use of ribosomal RNA (rRNA) sequences revolutionized our understanding of the phylogenetic relationships between living organisms.

<p>rRNA sequences are highly conserved and present in all living organisms. Comparing these sequences revealed the three domains of life: Bacteria, Archaea, and Eukarya.</p> Signup and view all the answers

Compare and contrast the nutritional modes found across the three domains of life (Bacteria, Archaea, and Eukarya).

<p>Bacteria and Archaea exhibit diverse nutrition, including autotrophy and heterotrophy. Eukarya contains organisms with heterotrophy (Animalia, Fungi) and autotrophy (Plantae), along with diverse strategies in Protista.</p> Signup and view all the answers

How do the unique membrane lipids found in Archaea contribute to their ability to thrive in extreme environments, compared to Bacteria and Eukarya?

<p>Archaea have branched hydrocarbons within their membrane lipids. This helps maintain membrane integrity at high temperatures and other extreme conditions, unlike the membranes of Bacteria and Eukarya.</p> Signup and view all the answers

Explain how the absence of membrane-enclosed organelles in prokaryotic cells (Bacteria and Archaea) affects their cellular processes compared to eukaryotic cells.

<p>The absence of membrane-enclosed organelles in prokaryotes means cellular processes occur within the cytoplasm, lacking the compartmentalization seen in eukaryotes, which can affect efficiency and regulation.</p> Signup and view all the answers

Discuss how the discovery of the three domains of life has changed the traditional five-kingdom classification system.

<p>The three-domain system (Bacteria, Archaea, Eukarya) revealed that prokaryotes are more diverse than previously thought, leading to the split of the Monera kingdom into Bacteria and Archaea.</p> Signup and view all the answers

Describe the significance of peptidoglycan within bacteria cell walls and explain why its absence in Archaea is evolutionary significant.

<p>Peptidoglycan provides rigidity and shape to bacterial cell walls. Its absence in Archaea indicates a distinct evolutionary path and adaptation to diverse and extreme environments.</p> Signup and view all the answers

Explain how the presence of histones associated with DNA in Archaea provides insights into the evolutionary relationship between Archaea and Eukarya.

<p>Histones are more common in Eukarya, but some species in Archaea contain histones associated with DNA. This supports the idea that Archaea and Eukarya share a more recent common ancestor.</p> Signup and view all the answers

Describe how the unicellular alga Chlamydomonas obtains nutrition and moves. How do these processes mirror the properties of the plant kingdom?

<p><em>Chlamydomonas</em> obtains nutrition via photosynthesis and moves using flagella. These processes demonstrates that they are autotrophic; however, plants are nonmotile.</p> Signup and view all the answers

Describe the cellular and nutritional differences of the Fungi kingdom from the Animalia kingdom.

<p><em>Fungi</em> are composed of heterotrophs, has cell walls made of chitin, and are nonmotile. The <em>Animalia</em> kingdom does not have cell walls, they are motile at some point in their life cycle, and are composed of heterotrophs.</p> Signup and view all the answers

Describe common features of cell types that the kingdoms Fungi, Protista, and Plantae kingdoms have in common.

<p>The <em>Protista</em>, <em>Plantae</em>, and <em>Fungi</em> kingdoms have cell walls. Also, all of these kingdoms have eukaryotic cell types.</p> Signup and view all the answers

Describe why antibiotics like streptomycin and chloramphenicol affect Bacteria by inhibiting growth, but have little to no effect on organisms of the Archaea and Eukarya domain.

<p>Streptomycin and chloramphenicol inhibits growth due to targeting certain traits of the bacteria. Archaea and Eukarya share traits that differ from bacteria, allowing them to have protection.</p> Signup and view all the answers

Explain how fungi obtain their essential nutrients.

<p>The <em>Fungi</em> kingdom uses digestive enzymes to digest and break down dead or decaying organic matter. It then absorbs small molecules into the cells.</p> Signup and view all the answers

A scientist discovers a new organism that is unicellular, lacks a nucleus, and has a cell wall containing a novel type of lipid. Based on this evidence, to which domain does this organism most likely belong?

<p>The new organism belongs in the <em>Archaea</em> domain. The domain <em>Archaea</em> lacks a nucleus, and has cell walls made of lipids.</p> Signup and view all the answers

How do light microscopes reveal a cell's components?

<p>Light microscopes use light to illuminate and magnify specimens, revealing cellular structures and components based on their light absorption and refraction properties.</p> Signup and view all the answers

How does electron microscopy reveal the fine structure of a cell?

<p>Electron microscopy uses beams of electrons to create highly magnified images of cells, revealing intricate details of cellular structures at the nanometer scale.</p> Signup and view all the answers

What are the key differences between the three domains of life? In other words, contrast Bacteria, Archaea, and Eukarya.

<p><em>Bacteria</em> and <em>Archaea</em> are prokaryotic domains, whereas <em>Eukarya</em> is a eukaryotic domain. Prokaryotic domains have thick cell walls, whereas eukaryotic domains do not have cell walls. Molecular machinery also varies between the domains.</p> Signup and view all the answers

How does the structure of a macrophage cell reflect its function in the body?

<p>Macrophages have an irregular shape and extend pseudopodia to engulf pathogens or cellular debris. This structure enables them to efficiently perform phagocytosis.</p> Signup and view all the answers

In what fundamental ways are single-celled organisms like bacteria and giant cells like Paramecium similar?

<p>Despite differences in size and complexity, they share a similar basic chemistry (DNA, RNA, protein) and perform all essential life functions within a single cell.</p> Signup and view all the answers

Describe how comparing sequences of 16S ribosomal RNA reveals new phylogenetic relations between organisms with shared history.

<p>The more similarities an organism shares with another in terms of ribosomal RNA, the phylogenetic relations of each increase. Scientists have discovered the three domains of life through usage of this method.</p> Signup and view all the answers

Can a bacterium contain chloroplasts? Why or why not?

<p>No, because bacteria are a part of the prokaryotic domain. Additionally, chloroplasts are organelles only found in the <em>Eukarya</em> domain.</p> Signup and view all the answers

Describe the major impact that Carl Woese's publications introduced that caused scientists to reshuffle life's organization.

<p>Woese discovered that there can be three domains of life with significant phylogenetic difference by evaluating ribosomal RNA. This changed classification schemes.</p> Signup and view all the answers

In the context of cell biology, what is meant by the phrase 'living cells are self-replicating collections of catalysts'?

<p>This means cells have the ability to make exact copies of themselves via autocatalytic processes that require catalysis. Catalysis is provided by proteins.</p> Signup and view all the answers

Flashcards

Cell Diversity

Cells vary significantly in appearance and function, reflecting their specialized roles in diverse organisms.

Basic Cell Chemistry

All living cells share a fundamental set of molecules and biochemical pathways, ensuring core life processes are uniform.

Self-Replication of Cells

Living cells use catalysts to replicate themselves, using proteins that make copies of the cell.

Common Ancestral Cell

All life on Earth today came from a single celled organism.

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Genes

Genes provide the fundamental instructions for a cell's function and behavior, guiding its development and activities.

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Light Microscope

The invention that allowed us to understand the cell.

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Central Dogma

The central dogma describes the flow of genetic information within a biological system.

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Domain Bacteria

Domain of unicellular and prokaryotic organisms with thick, rigid walls and peptidoglycan.

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Domain Archaea

Domain that is unicellular and prokaryotic and lives in extreme environments.

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Domain Eukarya

A domain of organisms with cells that contain a nucleus.

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Domain

A domain is a larger, more inclusive category than a kingdom.

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Fungi

Organisms that are heterotrophs, have cell walls of chitin, and can be unicellular or multicellular.

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Plantae

Multicellular organisms with cellulose cell walls that carry out photosynthesis.

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Animalia

Organisms that are multicellular and heterotrophic, lack cell walls, and can move at some point in their life cycle.

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Study Notes

  • Unit 1 introduces the topic of cells as the fundamental units of life.
  • The learning objectives include cell characteristics, structure and function, basic chemistry, evolution and origin, and microscopy techniques.

Unity and Diversity of Cells

  • Cells are diverse in appearance and function.
  • Living cells all share a similar basic chemistry.
  • Living cells are self-replicating collections of catalysts.
  • All living cells evolved from a single ancestral cell.
  • Genes provide instructions for cell form, function, behavior, and organism characteristics.

Cells Under the Microscope

  • The light microscope led to the discovery of cells.
  • Light microscopes reveal some cell components.
  • The fine structure of a cell is revealed by electron microscopy.

Cell Diversity

  • Cells come in different shapes and sizes, like nerve cells, paramecium, snapdragon flower petal cells, macrophage, and fission yeast.
  • Genetic information flows from DNA to RNA (transcription) and then from RNA to protein (translation); known as the central dogma.
  • The same basic biochemical machinery generates all life.
  • A bacterium, butterfly, rose, and dolphin are made of cells with similar chemistry and principles.
  • The appearance/behavior of a cell is dictated by protein molecules (structural supports, catalysts, and molecular motors).

Self-Replication and Evolution

  • DNA and RNA provide sequence information to produce proteins and copy themselves.
  • Proteins provide catalytic activity to synthesize DNA, RNA, and themselves.
  • The special relationship between DNA, RNA, and proteins allows for self-replication.
  • Present-day cells evolved from the same ancestor, with evolution explaining their fundamental similarities due to shared genetic instructions.

Domains of Life

  • Evolutionary classification is a dynamic science aiming to present all life on an evolutionary tree.
  • Genetic analysis led to the establishment of a new taxonomic category: the domain.
  • A domain is a larger category than a kingdom.
  • There are three domains: Bacteria (Eubacteria), Archaea (Archaebacteria), and Eukarya (Fungi, Plantae, Animalia, and "Protista").
  • The kingdom "Protista" is not a monophyletic group.

Domain Bacteria

  • Bacteria are unicellular and prokaryotic.
  • This domain corresponds to the kingdom Eubacteria.
  • Bacterial cells contain thick, rigid walls that surround a cell membrane containing peptidoglycans.
  • Bacteria are ecologically diverse, ranging from free-living soil organisms to deadly parasites, with varying oxygen requirements.

Domain Archaea

  • Archaea corresponds to the kingdom Archaebacteria.
  • Members are unicellular and prokaryotic, living in extreme conditions with volcanic hot springs, brine pools, and oxygen-devoid mud.
  • Cell walls lack peptidoglycan, and the cell membranes contain unusual lipids.

Domain Eukarya

  • Eukarya includes all organisms with a nucleus.
  • It comprises the kingdoms "Protista,” Fungi, Plantae, and Animalia.

Protists

  • Protista is a "catchall" group of eukaryotes that cannot be classified as fungi, plants, or animals.
  • This domain does not form a single clade and is divided into at least five clades.
  • The organisms are referred to as protists.

Protist Characteristics

  • Most are unicellular, but brown algae is multicellular.
  • They can be photosynthetic or heterotrophic.
  • Protists may display fungal, plant, or animal characteristics.

Fungi

  • Members are heterotrophs with cell walls containing chitin.
  • Most fungi feed on decaying matter, secrete digestive enzymes, and absorb smaller molecules.
  • Mushrooms and other recognizable fungi are multicellular, while yeasts are unicellular.

Plantae

  • Members of the kingdom Plantae are multicellular, have cell walls containing cellulose, and are autotrophic.
  • Plants conduct photosynthesis through chlorophyll.
  • They are nonmotile, and the plant kingdom is the sister group to red algae.
  • It includes green algae, mosses, ferns, cone-bearing, and flowering plants.

Animalia

  • Members of the kingdom Animalia are multicellular and heterotrophic.
  • Animal cells do not have cell walls.
  • Most animals can move about during their life cycle.
  • There is considerable diversity, and many species inhabit all parts of the planet.

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