25.1 A Review of the Eukaryotic Cell Flashcards
Describe features of the eukaryotic cell. (5)
figure 25.1 in the textbook
- energy metabolism that requires membrane stability is confined to organelles
- cytoskeleton enables cells to change shape by remodelling quickly
- nuclear membrane separates transcription and translation in eukaryotes
- vesicles building off from membranes transport materials into the cell in endocytosis, and release material from the cell in exocytosis
- network of membranes is able to change shape and package molecules and particles for transport within the cell
What organizes the eukaryotic cell?
internal protein scaffolding and dynamic membranes
All cells require a mechanisms to maintain spatial order in the cytoplasm.
What do bacteria and archaeons rely on?
What do eukaryotes rely on?
bacteria and archaeons: primarily on walls that support the cell from the outside, along with a relatively rigid framework of proteins within the cytoplasm
eukaryotes: (some eukaryotic cells have walls but many others, including the cells in our bodies, do not) mainly on an internal scaffolding of proteins to organize the cell, with most of those supports being microtubules composed of the protein tubulin and microfilaments of actin
What is the difference between a eukaryotic cytoskeleton and the protein framework of bacteria?
it can be remodelled quickly, enabling cells to change shape
What do dynamic cytoskeletons require?
dynamic membranes that enable the cell to continue functioning even as it changes shape; eukaryotes maintain within their cells a remarkably dynamic network of membranes called the endomembrane system
What does the endomembrane system include?
- nuclear envelope
- an assembly of membranes that runs through the cytoplasm called the endoplasmic reticulum and Golgi apparatus
- plasma membrane that surrounds the cytoplasm
How are all membranes of the endomembrane system interconnected?
either directly or by the movement of vesicles
many are also capable of changing shape rapidly
How are the different membranes of the endomembrane system interchangeable?
in the sense that material originally added to the ER may in time be transferred to the cell membrane or nuclear membrane
What do biologists like to say about membranes of eukaryotic cells?
they are in dynamic continuity
When are membranes stable?
only in the mitochondria and chloroplasts, as required for energy metabolism
What provides eukaryotes with new possibilities for movement?
in combination, the dynamic cytoskeleton and the membrane system
ie. amoebas extend finger-like projections that pull the rest of the cell forward
What else does the dynamic cytoskeleton and the membrane system enable?
enables eukaryotic cells to engulf molecules or particles, including other cells, in a process called endocytosis
prokaryotic cells cannot perform this
What is phagocytosis?
a specific form of endocytosis in which eukaryotic cells surround food particles and package them in vesicles that bud off from the cell membrane
when packaged this way, particles can be transported into the cell interior for digestion
*figure 25.2 textbook
What is exocytosis?
molecules or cytoplasmic waste formed within the cell are packaged in vesicles and moved to the cell surface for removal
Where are intracellular vesicles and the molecules they carry transported and how?
through the cytoplasm by means of molecular motors associated with the cytoskeleton
in this way, both nutrients and signalling molecules move through the cell at speeds much greater than diffusion allows
major consequence: eukaryotic cells can be much larger than most bacteria
Name another way that the cytoskeleton and membrane system are flexible.
a change in the expression of a few genes can change their shape and organization
this flexibility makes complex multicellularity possible
Describe gene expression in complex multicellular organisms.
patterns of gene expression can differ from cell to cell
a change in gene expression can modify the cytoskeleton and membranes of individual cells, enabling cells to function in different ways
Where is energy metabolism localized in eukaryotic cells?
in mitochondria and chloroplasts
How do eukaryotes obtain carbon and energy?
compared to prokaryotes, there are fairly limited ways:
metabolic processes that power eukaryotic cells take place only in specific organelles
- aerobic respiration in mitochondria
- photosynthesis in chloroplast
only limited anaerobic processing of food molecules takes place within the cytoplasm
What happens in the cytoplasm after eukaryotic cells engulf food particles and package them inside a vesicle to be transported to the cytoplasm?
enzymes break down the particles into molecules that can be processed by the mitochondria
What do single-celled eukaryotes feed on?
many feed on bacteria or other eukaryotic cells
What can eukaryotes exploit?
sources of food that are not readily available to bacterial heterotrophs, which feed on individual molecules
this ability opened up the great new ecological possibility of predation, which vastly increased the complexity of interactions among organisms
What does the structural flexibility of eukaryotic cells also allow?
photosynthetic eukaryotes to interact with their environment in ways that photosynthetic bacteria cannot
What can unicellular algae do?
move efficiently through surface waters vertically as well as horizontally and therefore can seek and exploit local patches of nutrients
What do diatoms do?
store nutrients in large internal vacuoles for later use when nutrient levels in the environment become low
Plants gave evolved multicellular bodies with many different cell types. Give an example.
specialized ell types working together can provide leaves high in the canopy of trees with water and nutrients from the soil in which the plants are rooted
thus supplied, leaves can capture sunlight many meters above the ground, giving plants a tremendous advantage on land
What do Bacteria and Archaea absorb quickly?
available nutrients, and both rapid deployment of metabolic enzymes and rapid production are key to exploiting patchily distributed nutrients
Why do DNA replication need to be fast?
for reproduction to be fast
Why is the speed of DNA replication limited?
because the majority of the cells’ DMA is organized in a single circular chromosome, and replication begins from only one site
as a result, selection favours those strains of Bacteria and Arcahea that retain only the genetic material vital to the organism
What type of chromosomes do eukaryotes have?
multiple linear chromosomes and eukaryotes can begin replication from many sites on each chromosome
on this basis, eukaryotes are able to replicate multiple strands of DNA simultaneously and rapidly
this ability relieves the evolutionary pressure for streamlining, allowing eukaryotic genomes to build up large amounts of DNA that do not code for proteins
Describe what has been learned about “junk DNA.”
although eukaryotic genomes do appear to contain truly junky DNA, at least some of the DNA that does not code for proteins functions in gene regulation
this regulatory DNA gives eukaryotes the fine control of gene expression required for both multicellular development and complex life cycles, two major features of eukaryotic diversity
What did the innovations of eukaryotes’ dynamic cytoskeleton and membrane systems do?
gave eukaryotes the structure required to support larger cells with complex shapes and the ability to ingest other cells
How did early unicellular eukaryotes gain a foothold in microbial ecosystems?
not by outcompeting bacteria and archaeons, but rather by evolving novel functions such as the capacity to remodel cell shape
What did eukaryotes’ evolved complex patterns of gene regulation do?
enabled unicellular eukaryotes to evolve complex life cycles and multicellular eukaryotes to generate multiple, interacting cell types during growth and development
How do eukaryotes generate and maintain genetic diversity within populations?
sex
What does sexual reproduction involve?
meiosis and the formation of gametes, and the subsequent fusion of gametes during fertilization
How does sex promote genetic variation? (2)
meiotic cell division results in gametes that are genetically unique
- each gamete has a combination of alleles different from the other gametes and from the parental cell as a result of recombination and independent assortment
in fertilization, new combinations of genes are brought together by the fusion of gametes
- a few eukaryotic groups have lost the capacity for sexual reproduction
- ie. bdelloid rotifers: genetic diversity is high, as it is maintained by high rates of horizontal gene transfer
Describe meiotic cell division.
- results in haploid cells
- sexual fusion brings two haploid cells together to produce a diploid cell
the life cycle of sexually reproducing eukaryotes, then, necessarily alternates between haploid and diploid states
What are haploid cells?
a cell with one complete set of chromosomes
What is a diploid cell?
a cell with two complete sets of chromosomes
Where do many single-celled eukaryotes normally exist?
in the haploid stage and reproduce asexually by mitotic cell division
ie. green alga Chlamydomonas
What is a zygote?
a diploid cell formed by the fusion of two gametes, under the right conditions such as starvation or other environmental stress
What is the function of a zygote formed by single-celled eukaryotes?
resting cell
it covers itself with a protective wall and then lies dormant until environmental conditions improve
in time, further signals from the environment induce meiotic cell division, resulting in four genetically distinct haploid cells that emerge from their protective coating to complete the life cycle
*figure 25.3 textbook
Give an example of a single-celled eukaryote that normally exist as diploid cells.
diatoms: single-celled eukaryotes commonly found in lakes, soils, and seawater
- most are diploid and reproduce asexually by mitotic cell division to make more diploid cells
How do eukaryotes generate and maintain genetic diversity within populations?
sex
What does sexual reproduction involve?
meiosis and the formation of gametes, and the subsequent fusion of gametes during fertilization
How does sex promote genetic variation? (2)
meiotic cell division results in gametes that are genetically unique
- each gamete has a combination of alleles different from the other gametes and from the parental cell as a result of recombination and independent assortment
in fertilization, new combinations of genes are brought together by the fusion of gametes
- a few eukaryotic groups have lost the capacity for sexual reproduction
- ie. bdelloid rotifers: genetic diversity is high, as it is maintained by high rates of horizontal gene transfer
Describe meiotic cell division.
- results in haploid cells
- sexual fusion brings two haploid cells together to produce a diploid cell
the life cycle of sexually reproducing eukaryotes, then, necessarily alternates between haploid and diploid states
What are haploid cells?
a cell with one complete set of chromosomes
What is a diploid cell?
a cell with two complete sets of chromosomes
Where do many single-celled eukaryotes normally exist?
in the haploid stage and reproduce asexually by mitotic cell division
ie. green alga Chlamydomonas
What is a zygote?
a diploid cell formed by the fusion of two gametes, under the right conditions such as starvation or other environmental stress
What is the function of a zygote formed by single-celled eukaryotes?
resting cell
it covers itself with a protective wall and then lies dormant until environmental conditions improve
in time, further signals from the environment induce meiotic cell division, resulting in four genetically distinct haploid cells that emerge from their protective coating to complete the life cycle
*figure 25.3 textbook
Give an example of a single-celled eukaryote that normally exists as diploid cells.
diatoms: single-celled eukaryotes commonly found in lakes, soils, and seawater
- most are diploid and reproduce asexually by mitotic cell division to make more diploid cells
Why do diatoms become smaller with each asexual division?
because their external mineralized skeletons constrain their growth
What happens once diatoms reach a critical size?
meiotic cell division is triggered, producing haploid gametes that fuse to regenerate the diploid state as a round, thick-walled cell
this cell eventually germinates to form an actively growing cell with a mineralized skeleton
What do short-lived gametes constitute?
in diatoms, short-lived gametes constitute the only haploid phase of the life cycle
How are the 2 life cycles, of Chlamydomonas and diatoms, similar?
- haploid cells fuse to form diploid cells
- diploid cells undergo meiotic cell division to generate haploid cells
- commonly include cells capable of persisting in a protected form when the environment becomes stressful
Describe animal zygotes.
zygote divides many time to form a multicellular diploid body before a small subset of cells within the body undergoes meiotic cell division to form haploid gametes (eggs and sperm)
during fertilization, the egg and sperm combine sexually to form a zygote
*figure 25.3 textbook
In animals and diatoms, what is the only haploid phase of the life cycle?
gamete
What are the phases of plant life cycles?
two multicellular phases: one haploid, one diploid
