Organelles Flashcards
(20 cards)
Nucleus and Nucleolus
- a large structure enclosed within a double membrane
which contains chromatin, the nucleolus and nucleoplasm.
*Major function: Houses
DNA that serves as the
genetic material for
directing protein
synthesis.
*The nucleolus functions
in the synthesis of
ribosomes
Nuclear envelope
- a double membrane boundary between the cytoplasm and nuclear contents – it is continuous with rough endoplasmic reticulum
Nuclear pores
small openings through the nuclear envelope. This allows the passage of materials
including RNA, protein, ions
and small water soluble
molecules
Cell Membrane
Double layer of phospholipids with proteins scattered
throughout.
Membrane proteins may function as receptors, channels,
carriers, enzymes, and anchors or identifiers.
Carbohydrates and lipids are important as cell lubricants,
as receptors and as part of a recognition system.
Passive Transport: no energy required
Osmosis/Diffusion/Facilitated diffusion/Filtration
Active Transport: energy required
Sodium-potassium pump/ Vesicular transport – endocytosis
and exocytosis
Cell Membrane Function
*Physical barrier: Acts as a flexible
boundary, protects cellular
contents and supports cell
structure. Phospholipid bilayer
separates substances inside and
outside the cell.
*Selective permeability: Regulates
entry and exit of ions, nutrients
and waste molecules through the
membrane.
*Electrochemical gradients:
Establishes and maintains an
electrical charge difference across
the plasma membrane.
*Communication: Contains
receptors that recognize and
respond to molecular signals.
Endocytosis
Process by which materials
brought into the cell
-> Phagocytosis (cell eating) -
Certain white blood cells, such as macrophages and neutrophils, are specialized for engulfing and removing matter such as bacteria, protozoa, dead cells, and unneeded extracellular constituents.
-> Pinocytosis (cell drinking) - most cells.
Smaller invaginations of the cell membrane
form and entrap extracellular fluid and its
dissolved contents.
-> Receptor mediated
endocytosis - Receptors for
many substances, such as low-
density lipoproteins and
protein hormones, are integral
membrane proteins at the cell
surface.
Exocytosis
- Process by which cellular
materials exit the cell. - Materials are packaged within
vesicles (small sac). - Vesicles fuse with the cell
membrane and release content
outside of cell . - Exocytosis is important in
expulsion of waste materials out
of the cell and in the secretion of
cellular products such as digestive
enzymes, hormones, mucus and
neurotransmitters.
RER Structure and Function
Structure:
Extensive interconnected membrane network (mostly cisternae in shape)
with ribosomes attached on the cytoplasmic surface.
Function:
* Important for synthesis of secretory proteins and membrane
proteins.
* Polypeptides are assembled on the bound ribosomes and
threaded into the ER lumen.
* Responsible for addition of carbohydrates to proteins.
* Folding of the polypeptide chain (conformation) occurs in
the ER lumen.
* Quality control (degradation proteases).
SER Structure and Function
Structure:
Extensive interconnected membrane network (mostly
tubular in shape) lacking ribosomes.
Function:
* Synthesises lipids (phospholipids, steroids),
common in glands e.g. sebaceous glands.
* Forms vesicles and peroxisomes.
* SER of striated muscle is used as calcium store
(important for contraction).
* Enzymes within SER can help eliminate toxins,
drugs, alcohol – prominent in liver cells.
* Carbohydrate metabolism.
Mitochondria Structure and Function
Structure:
Double-membrane organelles composed of phospholipids and proteins.
Five distinct parts -
1. Outer mitochondrial membrane.
2. Intermembrane space.
3. Inner mitochondrial membrane - contains ATP
synthase, the enzyme which generates ATP in
the matrix.
4. Cristae space (formed by infolding’s of the inner
membrane – increases SA).
5. Matrix (space within the inner membrane).
Functions:
Produce ATP (primary function)
Cell signaling
Cellular differentiation
Cell death (apoptosis)
Maintains control of the cell cycle and cell growth
Golgi Apparatus
Series of several elongated, flattened, saclike membranous structures -
cisternae
Major functions: modifies, packages and sorts materials that arrive from the ER
in transport vesicles; forms secretory vesicles and lysosomes
Has a ‘Cis’ (forming/receiving)
face and a ‘Trans’
(maturing/shipping) face.
‘Cis’ face is closest to, and is
formed by, vesicles from the
ER.
Products are modified as they
move through the stack from
‘cis’ to ‘trans’ face.
Products are sorted and tagged. Vesicles containing products bud off from ‘trans’ face towards the plasma membrane.
Endomembrane system
A collection of
membranous structures
involved in transport
within the cell. The main
components of the
endomembrane system are
endoplasmic reticulum,
Golgi apparatus, vesicles
and cell membrane and
nuclear envelope
Lysosomes
- Spherical-shaped membrane-bound organelles formed from the Golgi
apparatus containing hydrolytic enzymes. - Digests microbes or materials (e.g. ingested by the cell, worn-out
cellular components, or the entire cell). - Particularly abundant in cells with great phagocytic activity (e.g.
macrophages, neutrophils).
Peroxisomes
Small, spherical shaped membrane bound organelles that
provide a contained environment for detoxification of
harmful substances taken into the cell.
Peroxisomes contain oxidative enzymes.
Important in alcohol metabolism
Proteasomes
Large barrel shaped protein complexes located in both the
cytosol and the nucleus.
They degrade and digest damaged or unneeded proteins
and ensure quality of exported proteins.
Microvilli
*Numerous thin membrane folds projecting
from the free cell (apical) surface;
supported by actin microfilaments (1-3μm
long).
*Increase membrane surface area for greater
absorption (abundant in the small
intestine).
* Actin anchors to the terminal web which
stiffens the microvilli keeping the actin
bundles at right angles to the cell.
* Terminal web is composed of
intermediate filaments.
Cilia
*Short, numerous hair-like cellular appendages 10–15μm long with microtubules at the centre, which occur
on exposed membrane surfaces of some cells.
*Move substances (e.g., mucus, and dissolved materials) over the cell surface (motor protein dynein).
*Arranged as a ring of 9 special double microtubules with a pair of single microtubules at the centre.
*Respiratory tract and the female reproductive tract.
Flagella
- Long singular membrane extension
supported by microtubules. - Sperm cells are the only human cells
to use a flagellum. - Function: locomotion
- Same arrangement of microtubules
(9 double and 2 single central
microtubules). - Contain the motor protein dynein.
Cytoskeleton
Composed of:
*Microtubules (built from globular
protein turbulin)
*Microfilaments (actin filaments)
*Intermediate filaments (e.g.
keratin in epithelial cells, desmin
in muscle cells)
Functions:
*Structural – Provides structural support to cell, determines cell shape, stabilizes junctions between cells.
*Movement – Assists with cytosol streaming and cell motility, helps move organelles and materials throughout the
cell, helps move chromosomes during cell division.
Centrioles
A centriole is composed of short lengths of microtubules lying
parallel to one another and arranged around a central cavity to
form a cylinder.
Centrioles are located in, and form part of, the centrosome
where they are paired structures lying at right angles to one
another. In this context they are involved in spindle assembly
during mitosis. The centrosome is positioned in the cytoplasm
outside the nucleus but often near to it.
A single centriole is also to be found at the basal end of cilia and
flagella. In this context it is called a ‘basal body’ and is connected
with the growth and operation of the microtubules in a cilium or
flagellum.
