Lecture 7 - The Cell II Flashcards
Define a nucleoid
Discrete concentration of DNA located within the cell’s interior
Place, not a thing
define plasmids
small circular molecules of DNA that carry a small number of genes
describe pili
threadlike hollow structures that extend from one bacterial cell to another that allow the transfer of plasmids
describe cytosol
liquid found inside the cells
describe cytoplasm
area within the plasma membrane, which comprises of the cytosol, the mitochondria, plastids, and other organelles (but not their internal fluids and structures) but not the nucleus.
Are organelles within the endomembrane system distinct?
no, they are interconnected
how do organelles within the endomembrane system communicate?
by budding vesicles (small membrane enclosed sacs)
what does the endomembrane system include?
nuclear envelope, endoplasmic reticulum, Golgi apparatus and visicles
describe the nucleus
stores DNA
Describe the nuclear envelope
- defines the boundary of the nucleus
- consists of two membranes (inner and outer) is a lipid bilayer with associated proteins
describe nuclear pores
act as gateways allowing molecules to enter and leave the nucleus
describe the nucleolus
appears as a mass of densely stained granules and fibers
- site where rRNA is synthesized
- assembly site of large and small ribosomal subunits
are ribosomes part of the endomembrane system?
no
describe ribosomes
- complexes made of rRNA and proteins (forming large and small subunits)
- sites of protein synthesis, in which amino acids are assembled into polypetides
free ribosomes
found floating in the cytosol
* synthesize proteins that do not leave the inside of the cell*
bound ribosomes
attached to the endoplasmic reticulum membrane
synthesize proteins that are secreted or components of the plasma membrane
endoplasmic reticulum
- continuous with the nuclear envelope
- accounts for more than half of the total membrane in many eukaryotic cells
- two distinct regions of the ER that differ in structure and function
rough endoplasmic reticulum
- studded with ribosomes on the surface of the membrane
- site of synthesis of proteins that are to be secreted
- synthesis of membranes
smooth endoplasmic reticulum
- outer surface lacks ribosomes
- functions in diverse metabolic processes, which vary with cell type
- synthesis of lipids, metabolism of carbohydrates, detoxification of drugs and poisons, storage of calcium ions
testosterone, a steroid hormone is synthesized in the cells of the testes. These cells would therefore have extensive amounts of WHICH organelle?
SMOOTH E.R.
steroids = lipids
lipids are synthesized in the smooth E.R.
golgi apparatus
- looks like a series of flattened membrane sacs, called cisternae
- stacked cisternae are surrounded by many small vesicles
- not physically continuous with the E.R.
- next stop for most vesicles budding from the ER
primary roles of golgi apparatus
- further modifies the lipids and proteins produced by the ER
- acts as sorting station
- synthesis of carbohydrates
lysosomes
- specialized vesicles derived from the Golgi
- responsible for the intracellular digestion: degrade damaged or unneeded biomolecules, bacteria or other smaller organisms that have been engulfed
- uses digestive enzymes and an internal environment with an acidic pH
vacuoles
- large vesicles derived from the endoplasmic reticulum and Golgi apparatus
- perform a variety of functions:
- food vacuole - formed by phagocytosis
- contractile vacuole - in aquatic protists, pumps excess water
- central vacuole - in plants, holds materials
is the mitochondria part of the endomembrane system?
no
what happens in the mitochondria
cellular respiration: a metabolic process that uses oxygen to generate ATP by extracting energy from sugars, fats and other fuels
** cellular respiration happens in the inner membrane
how many mitochondria are in a cell?
some cells have a single large mitochondrion, more often a cell has hundreds to thousands of mitochondria (dependent on cell’s function)
tissues and organisms that require more energy have more mitochondria
describe the mitochondria (its build)
enclosed by two membranes; outer membrane is smooth, inner membrane has infoldings called cristae
- inner membrane divides mitochondrion into
- inner membrane space: narrow region between the inner and outer membrane
- mitochondrial matrix: contains enzymes, mitochondrial DNA and ribosomes.
do animals have chloroplasts?
no
chloroplasts
capture the energy of sunlight to synthesize sugars; a process known as photosynthesis
- surrounded by double membrane and have an internal membrane-bound compartments called thylakoid
thylakoid membrane
contains a specialized light-collecting molecules (eg. chloraphyll is the most common)
what categories of cytoskeleton are found in eukaryotes vs animal cells
found in all eukaryotes:
- microtubules
- microfilaments
found only in animal cells
- intermediate filaments
shape of microtubules
hollow rods constructed from protein dimer called tubulin
microtubules function
- shape and support the cell (compression resistant)
- serve as tracks along which organelles can move
- form cilia and flagella
- involved in separating the chromosomes during cell division
name examples of microtubules
- flagella
- cilia
flagella
- long, few
- has undulating motion that generates force in the same direction as the flagellum’s axis
cilia
- short, many
- work like oars, with alternating power and recovery strokes
centrosome
- region located near the nucleus of animal cells considered to be a “microtubule organizing center”
- are composed of 2 centrioles
- are responsible for moving organelles and pulling the cell apart during cell division in animal cells
do plants have a centrosome?
no
microfilament structure
- solid rods
- also called actin filaments as they are built from molecules of actin
- can form structural networks
microfilament function
TENSION BEARING
- 3D networks support cell shape (make up the core of microvilli)
- important component of muscle cells
- serve as tracks along which organelles with motor proteins can move
intermediate filaments structure
- found only in animal cells
- not as frequently disassembled or reassembled as microtubules or intermediate filaments
- especially sturdy (remain intact after cell death)
intermediate filaments function
- tension bearing
- reinforce the cell’s shape and fix the position of certain organelles
path of a membrane protein
- mRNA translated into polypeptide at a bound ribosome (on RER)
- Polypeptide moves through RER and eventually buds off as a vesicle
- vesicle moves along microtubules until it reaches Golgi apparatus where polypeptide is further altered
- final polypeptide moves through Golgi cisternae and eventually buds off as a vesicle
- vesicle moves along microtubules until it reaches membrane, where it will stay and perform its function
what is common in animal cells but not plant cells?
intermediate filaments, centrosome, centrioles
what is common in all plant cells but not all animal cells
chloroplasts
cell wall
central value
