Download Cell Structure

CLASSIFICATION OF LIVING ORGANISMS
Most Familiar organisms are made from Eukaryotic Cells
e.g.
plants
animal
fungi – including yeasts
protists – protozoa (animal-like single celled) e.g. paramecia
-algae (plant-like single/multi celled) e.g. algae
Plasma membrane
Pinocytotic vesicle
nucleus
cytoplasm
Centriole
Cytoplasm
Mitochondrion
lysosome Nuclear membrane
nucleolus
Nuclear pore
Chromatin
Food vacuole
Nucl;eolus
Smooth endoplasmic
reticulum
Rough ER
vesicle
Ribosome
Lysosome)
Golgi Body
Secretory vesicle
Smooth ER
Large
Plasmadesmata vacuole
ribosome
Golgi body
(dictyosome)
Nucleolus
Nuclear pore
Chromatin
Nuclear membrane
Secretory
vesicle
Chloroplast
Vacuole
membrane
Organelle
Nucleus
(nuclear pore
Nucleolus)
Mitochondrion
Rough Endoplasmic
Reticulum
Smooth Endoplasmic
reticulum
Golgi Body
Lysosome
Centriole
Chloroplast
Large Vacuole
P/A?
Function
Nucleus
Nucleolus
Nuclear pore
Cristae
Matrix
R.E.R.
Ribosome
Organelle
Nucleus
(nuclear pore
Nucleolus)
Mitochondrion
P/A?
Function
Nucleus
Nucleolus
Nuclear pore
Controls the cell, contains DNA in the form of chromsomes (chromatin)
Manufactures ribosomes, contains a lot of rRNA
Allows transfer of materials between nucleus and cytoplasm (esp. mRNA
Site of aerobic respiration
Cristae
Electron transfer chain, produces majority of ATP
Matrix
KREB’s Cycle
Rough Endoplasmic
Reticulum
R.E.R.
Smooth Endoplasmic
reticulum
Site of synthesis of some other macromolecules in particular lipids
Golgi Body
Transports proteins synthesized on the ribosome around cell in particular to
Golgi for packaging for secretion
Ribosome
Site of protein synthesis, mRNA translation
Packaging of macromolecules, especially proteins (enzymes, hormones, neurotransmitters)
for excretion from the cell
Lysosome
Contain digestive enzymes (e.g lysozyme), low pH,
Digest macromolecules , involved in autophagy.
Centriole
Found in pairs, made of microtubules,
Organizes spindle fibres on which chromsomes align during cell division.
Chloroplast
Large Vacuole
Site of photosynthesis
Light reactions –grana (thylakoid) membranes,
Dark reaction – stroma
Large storage vesicle, containing cell salts, pigments.
• Plasmodesmata are channels found in plant cells
which allow direct cytoplasmic connection
between adjacent plant cells.
• Middle Lamella –layer of “glue” between adjacent
plant cells which holds them together. Contains
pectins.
• Nucleosome – DNA string wrapped around a
histone protein bead. Necessary to allow DNA to
be packaged efficiently into the small volume of
the nucleus
Prokaryotic cells
Streptomyces coelicolor.
Helicobacter pyloriStomach uclers
The bacterium and its relatives produce most of
the natural antibiotics in current use, including
tetracycline and erythromycin. They also
generate compounds that are used to treat
cancer and suppress the immune system.
Mycobacterium tuberculosis –
Tuberculosis
Yersinia pestis –
Black death (plague)
Nesseiria meningitiis –
Meningitis
Bacteria 0.5-100m, Eukaryotes 10- 100 m
An Electron Micrograph of a bacterium
Bacteria are much more simply constructed – no
membrane bound organelles
COMMON BACTERIA SHAPES
•Spherical (coccus)
•Rod shaped (bacillus)
•Spiral (spirochaetes, helicobacter)
BASIC BACTERIAL STRUCTURES
pili
(fimbriae)
cytoplasm
flagellae
Major difference between prokaryotic cells and eukaryotic
cells
PLASMA MEMBRANE
Same as all membranes (bilipid layer)
Phospholipid composition may differ between bacteria
and eukaryotic cells.
•The Cytoplasm
No compartmentalisation (no internal mebranes ie. No ER)
All chemical reactions occur within it.
Efficient regulation of biochemistry needed (Jacob Monod).
Contains ribosomes (free floating) responsible for protein
synthesis –
different from eukaryotic ribosomes –
antibiotics (chloramphenicol, tetracycline, streptomycin)
can specifically target them.
ON
Repressor
molecule
OFF OFF
No Enzyme
is produced
ON
ON ON
LACTOSE
Enzyme is
produced
The Bacterial “Chromosome” - Nucleoid
A single, circle of DNA.
Packaged by folding – to reduce volume.
Functions
Contains genetic information.
Codes for bacterial proteins.
Replication
Bacteria reproduce by dividing (asexual)
DNA must be replicated
DNA simply copied (no MITOSIS - no chromosomes).
Extrachromosomal DNA – Plasmids
Structure
Circular DNA, smaller than nucleoid.
Size
~ 1000 - 200, 000 bp (c.f. 4,000,000 base pairs)
1-700 copies.
Function
Not normally essential,
Gives some advantage
e.g. antibiotic resistance.
e.g. conjugative plasmids - Allow exchange of DNA between bacteria
– antibiotic resistance can jump from one bacterial species to another.
The Cell Wall
General Properties
Cell wall resists swelling due to osmotic entry of water
Prevents osmotic lysis
Maintains shape
Structure and synthesis unique to prokaryotes.
The chemical structure of peptidoglycan
The NAM, NAG and amino acid side chain form PEPTIDOGLYCAN
Covalently bonded (strong) to form a repeating polymer.
The polymer is further strengthened by covalent cross links (peptide bridges)
between amino acids.
NAM – N acetyl muramic acid
NAG – N acetyl glucosamine
Two basic types of bacterial cell wall
structures – GRAM +ve
Gram +ve cells peptidoglycan is:
heavily cross-linked
 very thick
(peptidoglycan accounting for 50% of weight of cell
 and 90% of the weight of the cell wall)
20-80 nm thick.
Two basic types of bacterial cell wall
structures – GRAM -ve
In GRAM –ve (G-) bacteria
peptidoglycan much thinner
15-20% of the cell wall
intermittently cross-linked.
GRAM STAINING
Gram positive (G+) cells are purple and Gram negative (G-) cells
are red.
Cell Wall
Bleu D’avergne
Freely permeable to solutes, the openings in the mesh are large and all types of
molecules can pass through them.
Lysozyme ( tears and saliva) -attacks peptidoglycan. It
hydrolyzes the NAM - NAG linkage.
Penicillin inhibits cells wall synthesis.
The G+ cell wall is very sensitive to the action of lysozyme and
penicillin.
Penicillin is antibiotic of choice for infections caused by G+
organisms.
e.g. Streptococcus pyrogenes which causes strep throat.
BACTERIAL MOTILITY
Flagellum (ae) – used for movement
FIMBRIAE
FLAGELLUM
Fimbriae/ pili –concerned with cell adhesion
Special SEX pili – enable transfer of plasmids from one
bacteria to another – can on occasion cross species.
e.g staphylococcus - MRSA
SUMMARY
No true membrane bound nucleus – rather a nucleoid (folded)
No membrane bound organelles/ no compartmentalisation
Many free floating ribosomes
Cell walls made of peptidoglycan (G+/ G-)
Mucilaginous capsule can be present
Flagellae (movement)
Pili./ Fimbrae are other extracellular protrusions (adhesion/
transfer)