Theme 1 Flashcards
The major divisions of the living world are defined by:
cell characteristics
Eukaryotes and prokaryotes have what in common?
plasma membrane
What is the cytoskeleton?
- protein fibre networks support plasma membrane and organelles within cytoplasm, allowing movement and maintenance of spatial relationships within the cell among its elements
- also allows cell to control its shape and to move
- enables eukaryote cells to engulf food particles
The cytoskeleton is made up of?
microtubules, microfilaments, and intermediate filaments
What are microtubules?
hollow tubes formed from tubulin dimers
What are microfilaments?
double helix of actin monomers that are important in movement and intracellular transport
What are intermediate filaments?
strong fibers composed of intermediate filament proteins
Cilia and flagella
Cilia are short and abundant
Flagella are long and few
They are elements allowing the cell to move.
Cross section in cilium reveals the 9 + 2 arrangements of microtubules
Eukaryote Endomembrane System
- collective term for nuclear envelope, lysosomes, golgi apparatus, vacuoles, and endoplasmic reticulum
- series of flattened sacs and tubes formed of lipid bilayer membranes, directly interconnected or connected by moving vesicles
- general function is to compartmentalize the interior of the cell, thus isolating incompatible biochemical processes, and to transfer products b/w these compartments
- greatly increases available S.A for synthesis
Structure of Eukaryote Genome
- divided between a number of linear chromosomes
- allows for expression of genes on different parts of a single chromosome or on different chromosome (regulatory genes)
- allows cell differentiation and production of different tissue types
Mitochondria is:
- the site of oxidative phosphorylation in eukaryote cells
Chloroplasts are the site of:
photosynthesis in eukaryote cells
Mitochondria and chloroplasts greatly increase:
S.A available for their processes when compared to prokaryotes
Sexual Reproduction in eukaryotes
- fusion of 2 haploid gametes from 2 parents to form a new individual genetically different from either parent (vertical transmission)
- generates genetic diversity
What is the evidence for endosymbiotic origins?
- Circular DNA
- Independent fission (remove mitochondria or plastids from a eukaryote cell and it cannot produce new ones)
- Size (same as bacteria)
- Double membrane
- Certain proteins specific to bacteria cell membranes are also in mito/chloro membranes
- 70S ribosomes
Endosymbiotic hypothesis part 1:
- heterotrophic eukaryotes evolved first through union of ancestral archeon with aerobic alpha-proteobacterium which became mitochondrion
Endosymbiotic hypothesis part 2:
- autotrophic eukaryotes evolved from heterotrophic eukaryotes through union with photosynthetic cyanobacteria, which became chloroplasts
Endosymbiotic origin scenarios:
- Ancestral archaeon first evolved endomembrane system, then entered symbiosis with alpha-proteobacterium, which became mitochondrion
- Ancestral archaeon entered symbiosis with alkpha-proteobacterium, which became mitochondrion, then endomembrane system evolved subsequently
(2 makes more sense, but both possible)
What is the cube-square relationship?
- S.A and volume of a solid do not increase linearly with increase in linear dimensions:
- S.A is propotional to length^2
- vol is proportional to length^3
- S.A is proportional to volume^2/3
Constraining relationship of S.A/vol
- Exchange across membranes around or within a cell is by diffusion or active transport, both only work effectively over very short distances and are dependent on S.A
Why is the cube-square relationship a critical limiting relationship?
- is why cells are small
- rates at which materials enter and exit cell is function of its S.A
- rates at which gasses and nutrients are used and wastes produced are function of cell’s volume
- small cells can exchange materials more effectively with their environment than large ones
What is simple multicellularity?
- cell adhesion but little else
- structurally simple
What is complex multicellularity?
- cells adhere, communicate, differentiate and specialize for formation of tissue
Origins of multicellular life theories?
- Symbiotic theory: different species came together (unlikely)
- Syncytial theory: division without cytokinesis until a certain point then differentiation occurs (likely)
- Colonial theory: same species start living together eventually became one organism because it worked out so well, differentiated (MOST likely)
Complex multicellularity arose independently at least:
6 times in the history of life
Cyanobacteria, the Great Oxygenation Event
The rise in environmental oxygen gave a selective advantage to possession of mitochondria and aerobic respiration, which permitted multicellularity
Origins of multicellularity
- Most evolutionary models begin with flagellated unicellular organisms (choanoflagellates in case of animals)
- Required that cells divide up tasks, specialize
- Required that cells learn to communicate with one another (affect one another’s behaviour, influence one another’s development, coordinate complex actions)
Simple Multicellularity
- Evolved independently in multiple eukaryote lineages
- Few cell types, no bulk flow, no complex structures
Unicellular organisms must carry out all functions of metabolism, homeostasis, reproduction, repair etc. with the resources of a
single cell
Single isolated cells must deal directly with
their environment
Unicellular organisms can’t get very big because
cube-square relationship keeps them small
Selective Advantages of Multicellularity:
- Division of labour and economy of scale
- Increased size
- Complexity
Specific advantages of increased size:
- Avoid predation/eat larger things
- Exploit new environment, reach upwards
- Storage
- Increased feeding mechanisms/opportunities
- Protected internal environment that can be regulated
- Cells can specialize since the internal environment is protected
- New metabolic functions
- Enhanced motility
- Increased traction in wind/current
- Share info with other cells
Specific advantages of complexity:
- Predator/prey and host/parasite interactions
- An increased opportunity for diversity in form/function and niches
Challenges of being multicellular and large
- Surface area / Volume relationships
- Must create solutions to allow exchange and rapid transport
- Intercellular communication, cells must be able to communicate with one another
- Cell adhesion (cells must stick together)
- Structure and support (physical laws set limits on animal size and performance)
- Homeostasis (defend cells against hostile environment, maintain stable internal environment for internal cells)
- Reproduction and growth (the multicellular body must be able to produce new multicellular bodies)
Oxygen consumption increases with
body size
Adaptions for increasing surface area
- Gas exchange (highly folded structures to pack more surface area in small volume)
- Nutrient absorption (villi increase S.A area for absorption)
- Filtration (capillary beds provide extremely large cumulative surface area for exchange between blood and tissues)
Larger bodies must have long-range transport system to ensure that:
materials reach every square unit of the total membrane surface area for effective exchange across the total membrane surface
What is extracellular fluid?
all of the body’s water not found within cell plasma membranes
What is intracellular fluid?
all of the body’s water found within cells – liquid portion of cytoplasm
What are tight junctions?
junctions that penetrate cell membranes of adjacent cells, fix cells in place, prevent movement of liquids between cells
What are adherence junctions?
junctions of adjacent cells link to each other and to microfilaments underlying cell membranes
What are desmosomes?
adjacent cells link to one another and to intermediate filaments of cytoskeleton
What are gap junctions?
- adjacent cells form channels penetrating cell membranes of both cells
- Signalling molecules and water can be passed directly from cell to cell
- Cells can thus communicate with one another
Tissues
- Group of similar cells and extracellular substances working together to carry out a specific function for the organism as a whole
- Requires that cells attach to one another and communicate with one another
The organs of multicellular organisms are composed of:
basic tissue types, specialized in structure and functions to carry out different tasks for the organism as a whole
Collagen and connective tissues
- Connective tissues in animals consist of cells, extracellular matrix, and fibres
- Collagen is a fibrous protein found in animal connective tissues
- Forms fibres in polysaccharide matrix of connective tissues
Extracellular Matrix and Cells
- Basic matrix consists of glycoprotein/carbohydrate complexes – absorb water - penetrated by network of collagen fibres
- Glycoproteins and collagen fibres attach to cell membranes by transmembrane protein, integens, which are attached to cytoskeleton – allow ECM to communicate with cell
- Matrix produced and maintained by cells within it, influences the way in which cells interact with the rest of the body
