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Organelles and cell structure - Coggle Diagram
Organelles and cell structure
Cell theory
All cells
come from
pre-exisiting cells
Living organisms
are
composed of cells
.
Cells are the
smallest unit of life
Cell fractionation
Purpose:
used to
purify organelles
based on
size
and
density
, using
centrifugation
How its done:
i.
break open
the
plasma membrane
ii. liquid is poured into another tube and centrifuged at high speed
Nucleus --> Mitochondria --> ER --> Ribosomes
Nucleus
consists of
Nuclear pores
Function:
1.
allows exchange of substances
between nucleus and cytoplasm
exit:
mRNA, tRNA and ribosomal subunits
enter:
nucleotides, ribosomal proteins, hormones
Nucleolus
Function:
synthesis of
ribosomal RNA (rRNA)
via transcription
assembly of ribosomal subunits
, where proteins imported from the cytoplasm are assembled with rRNA into large and small ribosomal subunits
General structure and Function
Structure:
a. spherical or ovoid structure
b. largest organelle
c. enclosed by a double membrane
d. contains DNA
Function:
contains
genetic hereditary material
eg. DNA that must be reproduced and
passed on to daughter cells
during cell division
controls protein synthesis
by
transcribing information stored in DNA
to produce
mRNA
. mRNA will be transported to cytoplasm for translation into proteins.
Ribosomes
Structure:
Composed of
ribosomal proteins
and
ribosomal RNA
Ribosomal proteins
are synthesised by free ribosomes in the cytoplasm ->
imported to nucleolus
->
combine
with
rRNA
to form
ribosomal subunits
Ribosomal RNA (rRNA)
is synthesised in the
nucleolus
Eukaryotes
:
80s
ribosomes
(small 40s subunit + large 60s subunit)
Prokaryotes
:
70s
ribosomes
(small 30s subunit + large 50s subunit)
Free ribosomes:
make proteins for
use in the cytoplasm
or
transported into some organelles
Bound Ribosomes:
attached outside the ER
or nuclear envelope
make proteins that are
destined for insertion into the membrane
Function: site of protein synthesis
Endoplasmic Reticulum
General structure
Consists of a
network of membranous tubules and sacs
called
cisternae
ER membrane
separates the ER lumen/cisternal space
(internal compartment of the ER)
membrane of rough ER
Is
continuous
with
outer nuclear membrane
Smooth ER
Structure:
no ribosomes
attached
consists of
interconnecting membranous tubules
Functions
2. Involved in metabolism of carbohydrates
eg. enzymes embedded in SER membrane of liver cells hydrolyse glycogen to glucose
1. Synthesis of lipids, including steroids.
eg. cells in ovaries/testes that produce sex hormones, are enriched with smooth ER
3. Detoxification of drugs and other poisons in blood (liver cells)
-enzymes in SER can add hydroxyl group to drug molecules, making them more soluble and easier to excrete out the body
4. Stores calcium ions
eg. in muscle cells, SER pumps Ca2+ from cytosol to SER lumen. SER release Ca2+ ions into cytosol when muscle is stimulated by nerve impulse -> trigger muscular contraction
Rough ER
Structure:
cytosolic side of membrane studded
with ribosomes
consist of
interconnecting flattened sacs
Functions
3. Chemical modifications of secretory proteins:
eg. enzymes embedded in the RER -> short chains of carbohydrates are attached to the proteins formed in RER, form glycoprotein
1. Synthesis of two main types of proteins:
i.
secretory proteins
- proteins that secrete out of the cell
ii.
membrane proteins
- proteins that are incorporated into membranes of the ER, Goglgi Apparatus, vesicles or plasma membrane
2. Synthesis of new membranes:
RER grows in place by adding membrane proteins and phospholipids to its own membrane
Enzyme built into the RER assemble phospholipids from precursors in the cytosol
RER expands and is transferred in the form of transport vesicles to other compartments of the endomembrane system
Golgi apparatus
Structure:
consist of
flattened membranous sacs
called
cisternae
Three regions
i. cis face
located
nearest to the nucleus and ER
receives materials
from transport vesicles budding from ER
ii. trans face
located
closest to plasma membrane
packages molecules
in vesicles and
transports them out of the golgi apparatus
iii. Medial region
Functions
2. Synthesis and secretion of polysaccharides in plant cells
golgi apparatus of plant cell
produce extracellular polysaccharides
(eg. pectin) that are used as
components
of the
plant cell wall
1. Temporary storage, packing and transport of secretory proteins
products of ER modified during their transit from
cis
to
trans
of golgi apparatus
modifications
include removal of water, emulsification of lipids
products are concentrated and then bud off the golgi apparatus as secretory vesicles
3. Formation of lysosomes in animal cells
Lysosomal enzymes
synthesised in
RER
-> transported to
golgi apparatus
for further processing
->
golgi vesicles
containing processed enzymes bud off as primary lysosomes
Lysosomes
Structure:
membranous sacs
containing
hydrolytic enzymes
Functions
Enzymatic digestion of substances
i.
fuse
with another
membranous organelle
to
digest the contents
within
ii. release their enzyme
outside the cell
iii. release their enzyme
into the cytoplasm
of the cell
Processes
b. Autophagy
unwanted organelles within cells are removed
unwanted organelles enclosed by membrane from SER, fuses with lysosomes -> autophagic vacuole -> digest organelles
a. Phagocytosis
digestion of large food particles that have been engulfed into cell
food material enclosed by membrane -> food vacuole
primary lysosome fuses with food vacuole, digest contents
c. Autolysis
self-destruction of dying cells
usually occur after cell damage / cell death
lysosomal membrane rupture -> release enzymes into cytoplasm -> digest organelles
d. Exocytosis
digestion of other cells / materials outside the cell
primary lysosome moves towards cell surface
-> fuse with cell membrane to discharge hydrolytic enzyme
-> digest materials outside the cell
Mitochondria
Structure:
1. Rod-shaped / cylindrical
2. Double membrane
i. outer mitochondrial membrane
smooth continuous layer
permeable to small molecules and ions
ii. inner mitochondrial membrane
extensively infolded to form partitions:
cristae
permeable only to small uncharged molecules such as ATP, ADP, calcium
impermeable to glucose and NADH2
3. Two compartments
i. inter-membrane space
allows accumulation of protons (H+) -> create proton gradient -> help synthesis of ATP
ii. mitochondrial matrix
contains enzymes for oxidation of glucose, mitochondrial DNA, 70s ribosomes
Functions:
site of
aerobic cellular respiration
site of
synthesis of ATP
and other energy carrier molecules
Chloroplast
Structure:
1. Biconvex discs
2. Double membrane
3. Flattened interconnected sacs = thylakoids
have photosynthetic pigments (chlorophyll & carotenoids)
enzyme needed for ATP synthesis and proteins = electron carriers
4.
Thylakoids suspended in
Stroma
, an aqueous matrix
contains chloroplast DNA
70s ribosomes
many enzymes
liquid droplet (plastoglobule)
starch grains
5. Partitioned into three major compartments by internal membrane
i. Inter-membrane space bewteen inner and outer membrane
ii. stroma
iii. thylakoid space enclosed by the thylakoid membranes
Function:
Site of photosynthesis
trap light energy and convert it to chemical energy
Cytoskeleton
Microtubules
Microfilament
Intermediate filaments
Functions
Provide
mechanical support
to cell,
maintain shape
Provide
anchorage
for many organelles
Centrioles and centrosomes
Function:
organise spindle microtubules
in animal cells during
cell division
for
proper segregation of chromosomes to daughter cell