Saturday 8 November 2014

12th Lecture : 7/11/14

Topic : Eukaryotic microorganisms

Notes:
1) Eukaryotic cell envelope
  • consists of plasma membrane ( lipid bilayer )
  • unlike peptidoglycan in bacteria and archaea
  • cellulose, pectin and silica in photosynthetic algae
  • cellulose, chitin and glucan in fungi
  • Protozoa has pellicle, instead of cell wall
  • Animals have glycocalyx surrounding the cell membrane
2) Structure of Eukaryotic cells
  • Flagella ( long whip-like projection ) and cilia ( short whip-like projection )
- to move substances along cell surface
- 9+2 arrangement ( 9 pairs of microtubules in the ring and 2 single of microtubules at the center of the ring)
  • Cell membrane
- have different membrane protein with the prokaryotic membrane
- have carbohydrates which important in cell-cell recognition
- contain sterols which increase resistance to osmotic lysis
- endocytosis ( encircles particles outside of cell) and exocytosis ( cells release secretions)
  • Cytoplasm
- contain cytoskeleton which support, shape and movement
- cytoskeleton are made up of microfilament, microtubules and intermediate filament
- Microfilament consists of actin subunits, is the the smallest fibers
- Intermediate filament consists of fibrous subunits and anchor organelles in place, is the medium-sized fibres
- Microtubules consists of tubulin subunits, works in cell division and is the largest fibres
  • Ribosomes
- the site of protein synthesis
- made up of proteins and rRNA
- found free in cytoplasm or associated to rough endoplasmic reticulum
- Eukaryotic ribosomes (80S) ( 60S large subunits, 40S small subunits )
  • Organelles
a) Nucleus
- nuclear envelope ( double nuclear membrane)
- nuclear pores
- nucleoli ( dense region where ribosomes are made)
- DNA combined with histones can exist in two form : chromosomes and chromatin
- protect DNA
- ribosomes synthesis

b) Rough Endoplasmic Reticulum
- flat, interconnected, membrane sacs
- outer walls covered with ribosomes
- Synthesis and modification of protein
- Synthesis of cell and organells membrane

c) Smooth Endoplasmic Reticulum
- no ribosomes
- lipid synthesis
- breakdown of toxic compounds
- regulates sugar release from the liver into the blood
- calcium storage for cell and muscle contraction

d) Golgi Complex
- stacks of flattened membrane sacs
- work closely with ER to secrete proteins
- receive proteins in transport protein in ER
- modifies proteins
- packages and sends proteins to cell membrane
- packages digestive enzymes in lysosomes

e) Lysosomes
- released from golgi and optimum pH is about 5
- digest bacteria that can enter the cell
- self-destruction of cell
- contain enzymes to break various materials
- digestion of food particles
- destruction of foreign materials
- molecular garbage dump

f) Vacuole
- central vacuole, contractile vacuole, food or digestion vacuole
- central vacuole stores water, pigments, poisons, and starch
- contractile vacuole regulate water balance
- digestion vacuole fuses with lysosome to digest food particles

g) Chloroplast
- dics shape, with three membrane system
- site for photosynthesis
- carbon dioxide + water + sunlight = sugar + oxygen
-70S ribosome

h) Mitochondria
- rod shape organelle
- central role in ATP production through the degradation of organic compound
- contain their own DNA, 70S ribosome
- Sugar + Oxygen = Carbon dioxide + ATP + Water
- form inner and outer membrane, between the two membrane is inter membrane space, cristae is the inner membran extension, matrix is the inner liquid.

i) Peroxisomes
- oxidation of organic substances
- decompose hydrogen peroxide
- oxidize toxic substances

j) Centrosome
- pericentriolar and centrioles

3) Mitosis
- produces 2 daughter cells that are identical to the parent cell
Phases in mitosis:
a) interphase - chromosome are not visible
b) prophase - chromosome coil, nuclear membrane distingrate, spindle fibres form
c) metaphase - chromosome become aligned
d) anaphase - chromatids separate; the number of chromosome doubled
e) telophase - cells divide into two, chromosome uncoil, nuclear reform, spindle fibres diassembles.
f) G1 interphase - the chromosome has one chromatid
g) G2 interphase - the chromosome has two chromatid

4) Meiosis
- produce daughter cells that have half the number of chromosomes as the parent cell
- involve meiosis 1 and meiosis 2
- meiosis 1 - (the number of cells is doubled but the number of chromosome is not)
- meiosis 2 - (the number of chromosomes does not get reduced, this division is like mitosis)

Activities: Each group choose an organelle topic and conduct class activities based on the topic

My own explorace :
1) Amoeboid motion is a common mode of locomotion in Eukaryotic cells. It is like crawling-like movement involved the formation of pseudopodia. The cytoplasm slides and forms a pseudopodium in front to move the cell forward.
2) Why mitochondria need DNA and have the similar ribosomes to prokaryotic ribosomes?
Scientists believe that eukaryotes somehow being parasited by prokaryote and when this happened the prokaryotes somehow evaded being eaten by eukaryote and escaped from being killed by the eukaryotes' immune system. In fact, these prokaryotes actually provided such a large benefit to the new host eukaryote, then they were slowly incorporated into neccessary metabolism of the host cell. Therefore, the idea of a mitochondria being the descendants of prokaryotes is well-accepted.

Reflection:
We are familiar with these structures of eukaryotic cell and this lecture reminded me again about the structure of eukaryotic cell that I learnt in my Form 5 and Form 6. The activities conducted by each group in the class were interesting and meaningful. These activities made the lessons not to be so boring and easier for me to memorise and understand the structures.

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