Exam 1: Ch 4: Eukaryotes Flashcards
Nucleus
separated from cytoplasm by the nuclear envelope
− Composed of 2 membranes
− Perforated w/small regularly spaced pores
− Nucleolus – found in nucleoplasm; site of RNA synthesis; collection area for ribosomal subunits
Cytoplasmic membrane
Cytoplasmic membrane – typical bilayer of phospholipids in which protein molecules are embedded; serves as selectively permeable barrier
Cell wall
animals (including helminthes) and protozoa DO NOT have cell walls; fungi do
− Cell walls of fungi:
o Rigid and provide structural support and shape
o Different in chemical composition from prokaryotic cell walls
o Made of: chitin, glycoprotein, mixed glycans
Endoplasmic reticulum
series of microscopic tunnels; used in transport, protein folding, and protein & lipid synthesis (occurs in other sites too)
− RER – ribosomes are attached to its membrane surface
− SER – w/out ribosomes
Golgi apparatus
site of protein modification and shipping
Ribosomes
staging areas for protein synthesis
− Size and structure:
o Large and small subunits of ribonucleoprotein
o Eukaryotic ribosome is 80S (a combo of 60S and 40S subunits)
Cytoskeleton
flexible framework of molecules criss-crossing the cytoplasm
− Functions: anchoring organelles, moving RNA and vesicles, permitting shape changes, movement
Vesicles
lysosomes and vacuoles
Lysosomes
participate in the removal of cell debris and damaged tissue
o Contain a variety of enzymes involved in the intracellular digestion of food particles and protection against invading microorganisms
Vacuoles
membrane bound sacs; contain fluids or solid particles to be digested, excreted or stored
o Formed in phagocytic cells in response to food and other substances that have been engulfed
Mitochondria
generate energy for the cell
− Composed of smooth continuous outer membrane
− Inner membrane: has tubular inner folds called cristae
− Unique organelles:
o Divide independently of the cell
o Contain circular strands of DNA
o Have prokaryotic-sized 70S ribosomes
Cristae (in mitochondria)
In inner membrane
o Holds the enzymes and electron carriers of aerobic respiration
o Extracts chemical energy contained in nutrient molecules and makes ATP
Appendages for moving
flagella and cilia
− Locomotion via cilia and flagella is common in protozoa, many algae, and a few fungal and animal cells
Flagella
microtubules slide past each other creating a whipping motion that requires the expenditure of energy
o Motility: allows microorganisms to move toward nutrients and positive stimuli, and away from harmful substances and stimuli
o Types of eukaryotes these are found on: protozoa, many algae, and few fungal and animal cells
Cili
similar structure to flagella but are shorter and more numerous
o Occur all over the cell surface in rows; beat back and forth in “oarlike strokes”
o Found only on a single group of protozoa & in certain animal cells
Glycocalyx
outermost layer that comes into direct contact w/environment
− Usually composed of polysaccharides
− Appears as a network of fibers, a slime layer, or a capsule
− Functions: protection, adherence of cells to surfaces, reception of signals from other cells and the environment
The cell’s (nature’s) assembly line
the nucleus, ER and golgi
1. A segment of genetic code of DNA from nucleus is copied onto RNA → passed thru the nuclear pores to the RER
2. Synthesized proteins on RER are deposited into lumen → transported to golgi apparatus
3. Proteins in the golgi are chemically modified and packaged into vesicles to be used by the cell
− Book version:
o Nucleus governs/regulates all activities – directs these activities thru a structural and chemical network
Segment of DNA w/instructions for producing proteins → copied onto RNA → passed out thru nuclear pores directly to ribosomes on ER → specific proteins synthesized from the code → deposited in lumen of ER → transported to GA → chemically modified and packaged into vesicles to be used by cell in a variety of ways
Last common ancestor
neither prokaryotic or eukaryotic; both prokaryotes and eukaryotes evolved from this precursor cell
History:
− The first primitive eukaryotes were probably single celled and independent
− Later, cells began to aggregate and form colonies
− Cells became specialized within colonies
− Later, complex organisms evolved and individual cells lost the ability to survive on their own
~ only disease-causing eukaryotes will be discussed in this lecture: protozoa, fungi, helminths
Endosymbiosis
the more complex cell type most likely emerged when a LCA cell engulfed smaller prokaryotic cells and coexisted w/them
− Process:
- Larger cell engulfs the smaller one → smaller one survives and begins an endosymbiotic association
- Smaller prokaryote becomes established in its host’s cytoplasm and multiplies → can utilize aerobic metabolism and increase energy availability for the host
- Ancestral eukaryotic cell develops extensive membrane pouches → they become the ER and nuclear envelope
- Photosynthetic bacteria are also engulfed → they develop into chloroplasts
- The first eukaryotic cells have emerged
Evidence of endosymbiosis
Mitochondria:
o Are same size as bacteria
o Have one circular chromosome, just like bacteria
o Have 70S ribosomes just like bacteria
o Divide via binary fission like bacteria
Eukarya that cause disease
fungi, protozoa, helminths
Fungi
fungus penetrates the substrate and secretes enzymes that reduce it to small molecules that can be absorbed by cells
− Not photosynthetic
− Can utilize a large variety of nutrients
− Macroscopic fungi: mushrooms, puffballs, gill fungi
− Microscopic fungi: molds, yeasts
− Forms:
- unicellular - colonial - complex/multicellular (mushrooms, puffballs)
Yeasts, hyphae, molds
Yeasts
round to oval shape; asexual reproduction; budding; single cell
Hyphae
long threadlike cells found in bodies of filamentous fungi
Pseudohypha
chain of yeast cells
Morphology: Fungi
o Cells of microscopic fungi grow in loose associations or colonies
o Colonies of yeasts are much like bacteria (have soft uniform texture and appearance)
o Colonies of filamentous fungi have cottony, hairy or velvety texture
o Mycelium – the woven, intertwining mass of hyphae that makes up the body or colony of a mold
o Septa – segments/cross walls found in most fungi; allow the flow of organelles and nutrients btwn adjacent compartments
o Non-septa hyphae – consist of one, long, continuous cell
o Vegetative hyphae – responsible for the visible mass of growth
Reproductive strategies & spore formation: Fungi
reproductive/fertile hyphae produce spores
o Spores: responsible for reproduction; explicitly responsible for multiplication; help fungus gain genetic variation and to be disseminated into environment
• Can be dispersed thru the environment by air, water and living things
• Will germinate upon finding a favorable substrate → produce new fungus colony in short time
Spores
responsible for reproduction; explicitly responsible for multiplication; help fungus gain genetic variation and to be disseminated into environment
Protozoa
most are harmless, free-living inhabitants of water and soil; a few species are responsible for hundreds of millions of infections each year; classified together b/c of their similar characteristics instead of their genetic relatedness
“first animals”
single celled organisms
Nutrition & habitat range: Protozoa
o Parasites live on fluids of their host
o Main limiting factor for growth = availability of moisture (predominant habitats are fresh and marine water, soil, plants, and animals)
o Many protozoa can convert to resistant, dormant stage called a cyst
Life cycle & reproduction: Protozoa
o Trophozoite – motile feeding stage requiring ample food and moisture to stay active
o Cyst – dormant resting stage when conditions in the environment become unfavorable
• Resistant to heat, drying and chemicals
• Can be dispersed by air currents
• Important factor in the spread of disease
o Life cycle determines mode of transmission!
• Trichomonas vaginalis: STD, doesn’t form cysts so must be transmitted by intimate contact
• Entamoeba histolytica and Giardia lamblia: form cysts so are readily transmitted via contaminated water and food
o All protozoa reproduce by simple, asexual mitotic cell division
o Sexual reproduction occurs in most protozoa → results in new and different genetic combinations
Trophozoite
motile feeding stage requiring ample food and moisture to stay active
Cyst
dormant resting stage when conditions in the environment become unfavorable
• Resistant to heat, drying and chemicals
• Can be dispersed by air currents
• Important factor in the spread of disease
Helminths
include tapeworms, flukes and roundworms
− Adult specimens usually large enough to been seen w/naked eye
− Not all flatworms and roundworms are parasite – many live free in soil and water
− Most parasitic helminths spend part of their live in GI tract
Flatworms
have thin, often segmented body plan; divided into tapeworms and flukes
Roundworms
AKA: nematodes
elongated cylindrical unsegmented body
General worm morphology
multicellular animals; equipped w/organs and organ systems
o Most developed organs: reproductive tract
o Reduction in digestive, excretory, nervous and muscular systems
Life cycles and reproduction: Helminths
complete life cycle includes fertilized egg, larval, and adult stages
• Must transmit an infective form (egg or larva) to body of a host
• Intermediate host – the host in which the larva develops
• Definitive host – the host in which adulthood or mating occur
• Transport host – an intermediate host that experiences no parasitic development but is an essential link in the completion of the cycle
o Fertilized eggs: released to environment; provided w/protective shell and extra food to aid development into larva; vulnerable to heat, cold, drying, predators
o Certain helminthes can lay 200,000-25 million eggs/day to ensure completion of their life cycle
Sources for human infection: Helminths
contaminated food, water, soil, or infected animals
Route of infection: Helminths
oral intake or penetration of unbroken skin
Distribution and importance of parasitic worms
o ~ 50 species of helminthes parasitize humans
o Distributed in all areas of the world (higher incidence in tropical areas)
o Yearly estimate of cases: in the billions, not confined to developing countries
o North American estimate: >50 million helminth infections
