Cell Structure and Function Part I
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What are the 2 main type of cells?
Eukaryotic and Prokaryotic
What is the use of a Plasma Membrane?
Acts as a selective barrier and helps to regulate its internal composition
What are the characteristics of Eukaryotes?
- Contain membrane-bound organelles
- Compartmentalise portions of cytoplasm for specific functions
- Linear DNA
What are the characteristics of Prokaryotes?
- No nucleus
- No membrane bound organelles
- Singular Circular DNA
Conversion of units in microscopy?
1m = 100cm = 1000mm = 106
µm = 109
- 1mm=103 µm = 106nm
Advantages of compartmentalization i.e cells having membrane bound organelles?
Separates ions, enzymes and other molecules in the cytoplasm
Separates chemical reactions, allowing each compartment to perform a different function
Allows specialisation of cells
Allow high concentrations of enzymes and molecules to accumulate in specific compartments (enhance efficiency of reactions)
Each compartment has a surface for attachment of proteins for specific functions
Ability of light microscope to see fine details is called the _____?
Differences btwn light and electron microscope?
- Magnification for
- Light : 1000x
- Live and dead specimens
- Magnification for Electron : 1000,000x
- Dead specimens
Break cells open, separate by density and size
What kind of organelles sediment first?
- From densest to least dense
- Golgi Apparatus
Organelles that are double membrane bound?
Organelles that are single membrane bound?
- Golgi Apparatus
Non membrane bound organelles?
- Cell wall present
- Adjacent cells joined by middle lamella
- Plastids present
- Single large vacuole bound by tonoplast
- Nucleus at edge of cell
- Centrosome present
- Cell wall absent
- Lamella absent
- Plastids absent
- Numerous small vacuoles
- Nucleus centrally located
- Centrosome with centrioles present
What kind of membrane does the nuclear envelope contain?
Double membrane separated by perinuclear space
What are the pore present on nuclear envelope use for?
Movement of substances into and out of nucleoplasm
Nucleoplasm is a ___?
collodial ground substance
Nucleolus is a ___?
Dense region in nucleoplasm not bound by membrane
What does a nucleolus contain?
DNA that codes for rRNA hence involved in synthesis of ribosomes (synthesis of ribosomal subunits 40s and 60s)
Function of nucleus?
contains most of the genetic material in the form of chromatin
Chromatin is made up of?
DNA and histones(proteins)
What takes place at the nucleolus?
rRNA and ribsomes synthesis
Main role of nucleus?
- Directs protein synthesis by syntheizing mRNA according to instructions provided by DNA
- Control life processes by protein regulation and enzyme synthesis
- rRNA and ribsomes synthesis
- Contains genetic material of cell in form of chromatin
Where is the chloroplast found?
Eukaryotic Photosynthetic cells
Structure of chloroplast
- Double membrane
- Inner membrane enclose stroma
- Stroma - 40-80 darkly colored grana
Each granum composed of
thylakoids connected by tubes (intergrana) to adjacent grana
Thylakoid membranes contain
photosynthetic pigments, e- carriers, ATP synthase
Stroma contains ?
- 70S ribosomes
- Enzymes essential for Calvin Cycle
- Circular DNA
- Starch Granules
Function of chloroplast
Site of photosynthesis
Mitochondrion versus Mitochondria
- Be very careful how many the diagram points to in exam!
- Found in all aerobically respiring eukaryotic cells
Inner membrane of mitochondria
- is thrown into folds called cristae and project into gel-like matrix (increase surface area for proteins to attach to, increase rate of ATP synthesis)
- Enzymes, ribosomes and DNA molecules are found here
Inner surface of inner membrane
studded with proteins which are e- carriers and elementary particles (ATP synthase)
ATP synthase is?
Protein complex that acts as both a channel and an enzyme
Matrix (ground substance) contains
- 70S ribosome
- circular DNA
- enzymes involve in aerobic resp
Function of mitochondria
- Synthesis of ATP by Krebs cycle and oxidative phosphorylation
- Heat production
Mitochondria and chloroplast orginate from prokaryotes
70S ribosomes and circular DNA
most eukaryotic animal and plant cells
RER abundant in
cells which secrete proteins (beta cells of islets of langerhans)
SER abundant in
cells that involve in lipid metabolism (liver, testes i.e. testosterone steroid)
- membrane lined interconnected cavities (flattened sacs) = cisternae
- continuous with outer membrane of nuclear envelope
ribosomes attached on outer surface of membrane
site of protein synthesis
The proteins synthesised are then
passed into the lumen of the RER where they fold into their 3D configuration and modified before export or use in other parts of the cell
SER consists of
- interconnected membrane bound tubules (NO RIBOSOMES) (NOT FLATTENED SACS)
- Continuous with RER
Functions of RER
- Post translational modifications of proteins synthesised at the ribosomes
- Allow polypeptide to fold into 3D configuration
- Proteins in RER transport out of cell for use
- RER synthesise new membrane (transported to cell membrane)
Functions of SER
- Synthesise lipids (phospholipids and steroids i.e testosterone)
- Detoxification of drugs and poisons in liver cells
- Stores and releases calcium ions
- common in cells specialised for secretion
- Several stacks of membrane-lined flat sacs (cisternae)
- [NO RIBOSOMES NOT TUBULAR]
GA consists of 2 face
- Cis Face (receiving end)
- Trans Face (dispatching end)
Material from ER fuse with cis face and travels across cisterna by cisterna (gets modified by specific enzymes located on cisterna along the way) all the way to the trans face
Vesicles remain in the cell after pinching off from GA
Functions of GA
- Modify Sort Package substances for exocytosis or use within cells
- Synthesis of glycolipds (lipid metabolism)
- Plant i.e synthesise cell wall polysaccharides
is a bag of enzymes
digestive enzyme (synthesised by ribsomes attached to RER) responsible for hydrolysing complex chemical compounds into simpler ones
Function of Lysosomes
- digestion of ingested particles taken in by endocytosis
- disposal of defunt of surpus organelles
- cell autolysis
Synthesis and secretory of a secretory protein
The protein is synthesised at the ribosomes attached to the RER and then enter the lumen of the RER. They are modified and fused with the cis face of the GA via transport vesicles. It is then modified sort and packaged into secretory vesicles and buds off from the trans face of the GA. It fuses with the plasma membrane and is secreted through exocytosis.
Ribosomes can have
both prokaryotic (70S) and eukaryotic (80S)
Ribosomes are found in both
- the surface of RER membrane
- freely around the cytoplasm
Ribosomes made up of
ribonucleic acid (rRNA) & protein
Functions of Ribosomes
Site of protein synthesis where A.A are linked by peptide bonds
Proteins synthesised by free ribosomes
will function within cytoplasm
Proteins synthesed by ribosomes bound to RER
will be modified to form functional proteins most of the time for secretion out of cell
- unique to centrosome of animal cells
- lies at right angles
- usually is 1 pair
- dividing cells has 2 pair
give rise to basal bodies of cilia and flagella found in specialised cell
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