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Week 1 Lecture 3: Eukaryotes (Cells With A Nucleus) (Features in common…
Week 1 Lecture 3: Eukaryotes (Cells With A Nucleus)
Features unique for an animal cell
Other membrane-bound organelles
Peroxisomes
Small vacuoles
Centrioles
Features unique for a plant cell
Cell wall
Plasmids
Chloroplasts
Chromoplasts
Storage molecules that do contain pigments
Leucoplasts
Storage molecules that do not contain pigments
e.g.
amyloplasts
Leucoplasts that store
starch
Other membrane-bound organelles
Peroxisomes
Glyoxysomes
Vacuoles
Features in common for both animal and plant cells
Nucleus
Contains the
nucleolus
A subregion of the nucleus
Site of ribosome assembly from RNA and proteins
Where ribosomal genes are transcribed
Largest organelle (5 microns)
Location of most of the cell's DNA
DNA in long,
linear
strands covered with proteins called
histones
=
chromatin
, a fibrous complex
Prior to cell division (prometaphase), the chromatin becomes tightly compacted and
condensed
so that individual chromosomes are visible under a
light microscope
Types of chromatin
Euchromatin
Heterochromatin
When chromatin occurs in the form of exceedingly long, thin threads, it is now called
chromosomes
Different eukaryotic organisms have different number of chromosomes
Except the nucleolus, the contents of the nucleus (liquid and insoluble molecules) is called the
nucleoplasm
Surrounded by the
nuclear envelope
Double membrane (actually one membrane curled in half)
Outer membrane folds outwards into the cytoplasm
It is
continuous
with the membrane of another organelle, the
endoplasmic reticulum
Phospholipid bilayers
Separates DNA transcription (nucleus) from translation (cytoplasm)
Perforated by thousands of
nuclear
(annular)
pores
(75 nm in diameter)
Connects the nucleoplasm with the cytoplasm
Annular: 'lens-shaped'
Traffics proteins and RNAs going out and into the nucleus
Ultimately, allows RNA transcribed from DNA to leave the nucleus via the pores and go out into the cell to be translated into proteins
Regulatory function
Only some molecules can enter and exit and nucleus
Regulating the nucleus' information-processing functions
Each pore is lined with
8 proteins
Located where inner membrane curls around to become outer membrane
It is NOT a hole
Pores attached to nuclear lamina (nuclear skeleton)
Is attached and interacts with chromatin
Helps
support
the nuclear envelope to which the nuclear lamina is attached
This gives the nucleus its shape and maintains it
Pores evenly spaced over the nuclear envelope
The site of DNA replication (transcription)
Endomembrane system
Types of organelles...
Nuclear envelope
#
Golgi apparatus
4
functions
2.
Modifies, concentrates, packages and sorts proteins before being sent to intracellular or extracellular destinations
1.
Receives protein-containing vesicles from the RER
3.
Adds polysaccharides to
protein or lipid molecules
and modifies other carbohydrates that were attached to proteins in the RER
4.
Site of synthesis of some polysaccharides for plant cell walls
Lysosomes
Derived from the
Golgi apparatus
See Lecture 4
Plasma membrane
See
Lecture 4 – Lipids and Membranes
Endoplasmic reticulum (ER)
2
types
Smooth endoplasmic reticulum (SER)
Continuity with
portions
of the RER
More tubular, less like flattened sacs than RER
Cisternae are not as ordered
Lacks
ribosomes
4
functions
1.
Chemical modification of small molecules taken in by the cell that may be
toxic
to the cell (detoxifies)
The modification make the targeted molecules
more polar
1 more item...
2.
Site of glycogen degradation in
animal cells
3.
Site of lipid and steroid synthesis
4.
Stores calcium ions (as the sarcoplasmic reticulum)
When Ca2+ is released, muscle contraction occurs
Rough endoplasmic reticulum (RER)
Presence of ribosomes attached to the outer surface of the RER membrane
Hence a 'rough' appearance – seen in
electron microscopy
Involved in protein synthesis
Synthesis of membrane-bound proteins (protein-containing vesicles)
3 more items...
Cells that synthesise a lot of proteins for export usually have abundant RER
3 more items...
The folding allows for a surface area many times greater than that of the plasma membrane
The interior compartment of the ER, the
lumen
is separate and
distinct
from the cytoplasm
Certain proteins synthesised in the RER are chemically modified with the lumen of the SER
Consists of membrane cisternae (tubes, and flattened sacs) that branch throughout the cytoplasm.
Allows for internal compartments and channels
Interconnected
system of membrane-enclosed
compartments
sometimes flattened into sheets or other characteristic shapes
Membrane components have a
dynamic structure
It is ever changing in structure and shape, with some parts of the membrane shifting to other endomembrane organelles
All of these membranes are therefore
functionally related
Transport of substances between the various components of the endomembrane system is achieved via
vesicles
Functions of intracellular membranes
1.
Provide a surface (lots of surface area) for biochemical reactions
2.
Establish a number of compartments to
prevent mixing
3.
Provide
transport of materials
Within the cell
From the cell to its exterior
From the cell to an adjacent cell
Cell to cell communication via proteins/hormones
Mitochondria
Ribosomes
Site of protein synthesis
More precisely, site of
translation
, where an mRNA sequence is 'translated' to a protein sequence
Composed of numerous proteins and several RNAs
25-30 nm
Places ribosomes can be found...
Free in cytoplasm
Attached to rough ER
Inside the mitochondria
Cytoskeleton