Unit 2 - Cells and Tissue Flashcards
Describe the difference in internal membranes between pro/eukaryotic cells
prokaryotic - internal membranes are not common, except for photosynthetic bacteria that have internal membranes specialised for harnessing light energy
eukaryotic - internal array of membranes that define the organelles that divide the cell into smaller spaces specialised for different functions
difference between cytosol and cytoplasm
cytoplasm - the entire contents of a cell other than the nucleus
cytosol - jelly like internal environment that surrounds the organelles
Difference in plant and animal organelles
Animal - nucleus, endoplasmic reticulum, golgi apparatus, lysosomes
Plant - cell wall, vacuoles for water uptake, chloroplasts for energy conversion, plasmodesmata (channels allowing the passage of large molecules such as mRNA and proteins between neighbouring cells)
are organelles isolated entities
no. the are either physically connected by membrane bridges or transiently connected by vesicles (small membrane enclosed scas that transport substances within a cell or from the interior to the exterior of the cell
how do vesicles form
by budding off an organelle, taking with them a piece of the membrane and internal contents of the organelle that they derived from. they then fuse with another organelle of the cell membrane, reforming a continuous membrane and unloading their contents
What does the endomembrane system consist of
the nuclear envelope, ER, golgi apparatus, lysosomes, cell membrane, vesicles
what is specific to plants concerning the endomembrane system
The endomembrane system is continuous between cells through plasmodesmata
Define 1. exocytosis and 2. endocytosis
- when a vesicle fuses with the cell membrane, providing the vesicle with a way to empty its contents to the extracellular matrix or deliver proteins embedded in the vesicle membrane to the cell membrane
- budding off from the cell membrane and bringing enclosed material from the outside of the cell into the cell interior
nuclear membrane
double membrane that surrounds the nucleus, containing nuclear pores
nuclear pores
openings in the nuclear envelope that transport proteins (transcription factors) into the nucleus and mRNA out of the nucleus to the cytosol - the mRNA binds to ribosomes or stay free in the cytosol -
where does protein synthesis occur
in the cytosol, free ribosomes in cytosol associated with the ER
Endoplasmic Reticulum
Physically continuous with the nuclear envelope, interior (lumen) is continuous throughout. very convoluted membrane for larger SA
involved in protein and lipid synthesis.
produces and transports many of the proteins and lipids used inside and outside the cell (including transmembrane proteins)
Rough ER
has ribosomes
synthesizes transmembrane proteins, proteins that end up in the interior of the organelles and proteins destined for secretion
cells that secrete large quantities of proteins have extensive rough ER (eg cells of the gut that secrete digestive enzymes, and cells of the pancreas that secrete insulin)
Smooth ER
lacks ribosomes
site of fatty acid and phospholipid biosynthesis
more common in cells that produce lipids (eg cells that synthesize steroid hormone, as they produce cholesterol)
Golgi Apparatus
three primary roles:
1. further modifying proteins (with enzymes) and lipids produced by the ER
2. acts as a sorting station as these proteins and lipids move to their final destinations
3. the major site where carbohydrates are added to proteins and lipids
made up of flattened membrane sacs called cisternae
vesicles are the primary way that proteins move through the golgi apparatus with to their final destination
Where do Lysosomes originate from
They are specialised vesicles derived from the golgi apparatus
What is the function of lysosomes
They degrade damaged or unneeded macromolecules. therefore playing a key role in intracellular digestion and the recycling of organic compounds. they’re also involved in apoptosis (programmed cell death)
How do lysosomes break down molecules
They contain a variety of hydrolytic enzymes that are packaged into lysosomes by the golgi apparatus. The golgi apparatus also packages the macromolecules that are destined for degradation
what is the optimal internal environment of proton pumps
pH 5 (acidic)
How does the cell protect the organelles from being degraded by the lysosomes
By having an environment of pH 7, in which the lysosomal enzymes cannot function
What do mitochondria do
harness energy from chemical compounds such as sugars and convert it into ATP. A proton electrochemical gradient is used to synthesize ATP for use by the cell
Describe the structure of mitochondria
Two membranes, an outer membrane and a highly convoluted inner membrane whose folds project into the interior.
These folds allow for a greater surface area available for the biochemical machinery that pumps protons and then synthesizes ATP
What do chloroplasts do
capture the energy of sunlight to synthesize simple sugars (this process is called photosynthesis) results in the release of O2
describe the structure of chloroplasts
surrounded by a double membrane, and have a third, internal membrane, called the thylakoid membrane
What does the thylakoid membrane do
it separates the internal compartment called the thylakoid, the membrane contains specialised light collecting molecules called pigments (chlorophyll)
describe the function of chlorophyll
collects light energy, which enzymes in the chloroplast then use CO2 as a carbon source for carbohydrates
What are the functions of vacuoles in animal and plant cells
animal - help get rid of waste products
plants - help maintain water balance
What roll does vacuoles play in homeostasis
They regulate the turgidity by regulating the amount of water in a cell. they will absorb water and diffuse it out of the cell if it is in excess, if the cells lacks water the vacuole tends to revert it back into the cell
What four types of tissue do animals have
- epithelial
- connective
- nervous
- muscle
they combine to form organs
What determines the shapes of cells in animals
Maintained and determined by structural protein networks in the cytoplasm called the cytoskeleton
What are cell junctions
complexes of proteins in the cell membrane where a cell makes contact with another cell or the extracellular matrix
what is the extracellular matrix and what is its importance
A meshwork of proteins and polysaccharides outside of many cells and tissues. It are important in maintaining a strong, properly shaped tissue or organ
What is endosymbiotic theory
The theory states that the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria (prokaryote). This theory explains the origin of eukaryotic cells.
What is the main role of the cytoskeleton
Provides internal support for the cellsh
What two cytoskeletal elements do all eukaryotes have
microfilaments and microtubules (animals cells also have a third element, intermediate filaments)
What are these filaments made of
long chains, or polymers, made up of protein subunits
what are the functions of the microtubules, and microfilaments
structural support, and enabling cells to change shape, move about, and transport substances
which part of the cytoskeleton is the smallest
the microfilaments (7nm diameter)
What are microfilaments made of and what do they do
Actin monomers, arranged to form a helix.
- extensively branched in the area just below the cell membrane, reinforcing this area (the cell cortex) and helping to organize proteins associated with it
- play important role in maintaining cells shape
what is the main function of intermediate filaments and what allows them to do this
providing the cell with mechanical strength - they are polymers made of intermediate filament proteins that combine to form a strong cable like structure
what are intermediate filaments made from
it varies
epithelial - keratins
fibroblasts - vimentins
neurons - neurofilaments
what is the largest of the 3 cytoskeletal elements
microtubules
what are microtubules made from
protein dimers (each made up of two different tubulin proteins) alpha and beta tubulin
What specific structure are the microtubules connected to in animal cells
the centrosome
what is the function of microtubules
help maintain cell shape and internal structure
what is dynamic instability and why does it occur
the process of microtubules undergoing seemingly random cycles of repaid depolymerization and then by slower polymerization - this allows spindle microtubules to quickly find and attach to chromosomes during cell division
difference in plus and minus end of microtubules
plus end undergoes rapid polymerization
minus end undergoes slow polymerization
what else assists microtubules in the depolymerization/polymerization
motor proteins
which motor proteins are associated with which element of the cytoskeleton
- Microfilaments = myosin
- Microtubules = kinesin & dynein
what do the different motor proteins do
- myosin - transport cellular cargo (such as vesicles), also responsible for changes in shape of many types of cells (contracting of muscle cells - which depends on the interaction of myosin with microfilaments and powered by ATP)
- kinesin - transports cargo toward the plus end of the microtubules, located at the periphery of the cell
- dynein - transports cargo away from the cell membrane toward the minus end, located at the centrosome in the interior of the cell
what drives the kinesin and dynein
driven by conformational changes in the motor proteins and powered by energy harvested from ATP
give an example of kinesin and dynein working
colour change in zebrafish embryos. melanin granules are redistributed along microtubules in the melanophores of the skin, driven by kinesin and dynein
what are cilia
rod-like structures that extend from the surface of cells and are well conserved across the eukaryot
What are the functions of nonmotile cilia and give an example
sensory function - taking in the environmental signals and transducing them to the cell interior
eg. found in mammalian olfactory neurons in the nose and photoreceptors in the eyes
what is the function of motile cilia and give an example
to propel the movement of cells or fluid surrounding the cell
eg. green algae and paramecium, where cilia propel the organisms through water. and in sperm cells (flagella)
what role does cilia play in protecting us from pathogens
they are present in epithelial cells (line the supper respiratory tract) where they move the fluid above the surface of the cell layer, carrying away foreign particles and pathogens
what motor protein is associated with the movement of cilia
microtubules associate with dynein, which causes the microtubules to bend, causing a wavelike motion of the cilia
What are cell adhesion molecules
proteins on the surface of cells that recognize and attach cells to each other or to the extracellular matrix
what is the most important example of a cell adhesion molecule
cadherins (calcium-dependent adherence proteins)
what kind of proteins are cadherins
transmembrane proteins
What do cadherins connect together, what does this result in and how do they do this
- they connect the cytoskeleton of one cell to the cytoskeleton of another
- increasing the strength of tissues and organs
- the extracellular domain of a cadherin binds to the extracellular domain of a cadherin of the same type on an adjacent cell. the intracellular domain of the cadherin is linked to the cytoskeleton (including microfilaments and intermediate filaments)
what are integrins
they are transmembrane proteins, and cell adhesion molecules that allow cells to attach to proteins of the extracellular matrix.
they also act as receptors that communicate info about the extracellular matrix to the interior of the cell.
What are the two types of anchoring cell junctions
adherens junctions and desmosomes
What cell junction are microfilaments attached the cell membrane and epithelial cells with
adherens junction
what is the difference between adherens and desmosomes
adherens - form a belt around the circumference of cells
desmosomes - buttonlike points of adhesion
what is the specific role of tight junctions
they prevent materials from passing freely through the spaces between the cells - they establish a seal between cells that prevents molecules from moving through the channel
What makes up tight junctions
integral membrane proteins (claudins and occludins)
what two regions does a tight junction divide the cell membrane into
apical - which is in contact with the lumen
basolateral - the bottom and sides of the cell
what causes the different regions of tight junctions to have different functions
the fact that they have different integral membrane proteins
what other function can cell junctions have, give examples of these junctions
permitting materials to pass directly from the cytoplasm of one cell to the cytoplasm of another, allowing cells to communicate with each other.
gap junctions (animal cells) and plasmodesmata (plant cells)
what makes up gap junctions
a complex of integral membrane proteins called connexins arranged in a ring
what allows/causes the movement of molecules through these gap junctions
ions and signaling molecules
What are plasmodesmata and what are their functions
passages through the cell walls of adjacent plant cells. they allow cells to exchange ions and small molecules
what is the size of plasmodesmata for
large enough for cells to transfer RNA molecules and proteins
What is the function of the extracellular matrix
provides a molecular framework that helps determine the structural architecture of plants and animals. provides structural support and info cues that determine the activity of the cells that are in contact with it
what is the extracellular matrix composed of
proteins, polysaccharidesh
what is the animal extracellular matrix composed of
large fibrous proteins, including collagen, elastin, laminin (strength)
how does the matrix protect against compression and other physical stress
the matrix is negatively charged, attracting positively charged ions and water molecules that provide this protection
what are the two functions of connective tissue
- physically connects various parts of the body - eg. tendons that connect your muscles to bones, or ligaments that connect your bones to other bones
- supports various parts of the body (underlies all epithelial tissue) - eg. dermis of the skin is connective tissue, that provides support and nutrients to the overlying epidermis
what role does the extracellular matrix play in synthesizing of connective tissue
it determines the properties of differnt connective tissue due to being dominant in the tissue
which cell in the dermis synthesizes most of the extracellular matrix
fibroblasts
what is the most abundant protein in the extracellular matrix of animals
collagen (25% of all the proteins in our body)
what type of collagen is the most abundant in our body
Type I collagen found in the dermis of the skin
what does type I collagen do
provides strong, durable support for the epidermis
what gives collagen the ability to provide strength
its rope like structure, it is composed of intertwined fibres that makes it much stronger than a single fibre of the same diameter
What is the extracellular matrix in plants
it forms the cell wall
what is the main component of of the plant cell wall
polysaccharide cellulose
what is the function of cell walls in plants
maintains the shape and turgor pressure of plant cells and acts as a barrier that prevents foreign materials and pathogens from reaching the cell membrane
what are the 3 layers making up the plant cell wall
- Outermost Middle Lamella - synthesized first (during late stage cell division) & composed of a glue-like complex carbohydrate, which is the main mechanism by which plant cells adhere to one another
- Primary Cell Wall - laid down while the cells are still growing, consisting of mainly cellulose (but also others, eg. pectin) & assembled by enzymes on the cell surface, remains flexible and thin
- Secondary Cell Wall - constructed when cell growth has stopped, located closest to the cell membrane, made largely of cellulose (but also contains lignin - the lignin hardens the cell wall, making it water resistant), & in woody plants the cell wall can be as much as 25% lignin, allowing them to grow to great heights
