anatomy of the cell

Question 1

what are features common to all eukaryotic cells?

Answer 1

membrane
cytosol 
cytoskeleton
organelles 
inclusions (may or may not be membrane bound)

Question 2

what separates the cytoplasm from the outside environment ?

Answer 2

plasmalemma

Question 3

what is the plasmalemma

Answer 3

> bimolecular layer of amphipathic phospholipid molecules with hydrophilic heads at the outer and inner surfaces, and hydrophobic fatty acid chains facing the middles of the 2 layers
contains integral proteins which the cells inserts into the membrane
has the ability to exocytose and endocytose

Question 4

what is the difference between organelles and inclusions?

Answer 4

> organelles are essential to life - they are intracellular organs with specific functions and structural organisation ie mitochondria, lysosomes, golgi apparatus

> inclusions are dispensable and usually represent components that have been synthesised by the cell itself or even waste products ie glycogen stores

**both are found in the cytoplasm

Question 5

what is the cytoskeleton?

Answer 5

> gives the cell structural integrity

Question 6

how does the cell keep its structure?

Answer 6

> the cytoskeletal proteins….
they are filamentous proteins that become attached to each other by anchoring and joining other proteins to build up an internal sort of scaffold

Question 7

what are the three main classes of filaments?

Answer 7

microfilaments (actin)
intermediate filaments (six main proteins)
microtubules (tubulin proteins)

Question 8

what are the three main classes of filaments?

Answer 8

> microfilaments (actin)
intermediate filaments (six main proteins)
microtubules (tubulin proteins)

Question 9

what are the three main classes of filaments?

Answer 9

> microfilaments (actin, the smallest ie 7nm per micron)
-globular actin polymerises to form filamentous actin
intermediate filaments (six main proteins, medium-ish ie 10-15nm)
-provides a lot of the structure, there’s lots if different types ie different cells express different intermediate filaments ie can trace origin of cells (think invading tumours)
microtubules (tubulin proteins, the largest)
-alpha and beta subunits that assemble and disassemble very well,
originate from the centrosome, and include stabilising microtubule associated proteins ie MAPS

Question 10

why are microtubules so important?

Answer 10

> they are important in cilia flagella and the mitotic spindle
they serve as the motorway network in the cell
-dynein and kinesin attach to the microtubules and move along them ie the associate with the membranes of organelles and drag them along the microtubule
(kinesin - an ATPase the moves toward the cell periphery)
(dynein - an ATPase the moves toward the cell centre)

Question 11

what encloses the nucleus?

Answer 11

a nuclear envelope composed of an outer nuclear membrane and an inner nuclear membrane with nuclear pores

Question 12

where can the perinuclear cistern be located?

and what is it continuous with

Answer 12

between the inner and outer nuclear membrane

-is continuous with the cistern of the endoplasmic reticulum

Question 13

which nuclear membrane is studded with ribosomes?

Answer 13

outer

-the outer is continuous with the rough endoplasmic reticulum

Question 14

RNA synthesis takes place where?

Answer 14

the nucleus - as it contains chromosomes

> both mRNA and tRNA are transcribed in the nucleus
rRNA is transcribed in the nucleolus

Question 15

which type of DNA is more dispersed?

Answer 15

euchromatin
-is actively undergoing transcription

heterochromatin is DNA that is highly condensed and not being transcribed

Question 16

what is the endoplasmic reticulum

Answer 16

forms a network of interconnecting membrane bound compartments in the cell.
RER and SER

Question 17

what is the difference between the RER and the SER

Answer 17

> RER is studded with ribosomes, ie plays a vital role in protein synthesis and initiation of glycoprotein formation
ie more RER indicates a cell that is producing protein
SER is important in the synthesis of lipids

Question 18

explain the golgi apparatus complex

Answer 18

the ‘finishing line’ in the production in the cell

• is composed of flattened membrane bound cisternae
• transport vesicles arrive at the golgi from RER/SER
• golgi cisterns function in the modification and packaging of macromolecules , it adds sugars, cleaves some proteins and sorts macromolecules into vesicles

Question 19

explain mitochondria

Answer 19

• the inner membrane is folded to form cristae ie increased surface area
• they function in the generation of ATP and in the synthesis of certain lipids and proteins
• all cells contain mitochondria
• *they contain their own DNA and system for protein production

Question 20

what are intercellular junctions

Answer 20

specialised membrane structures which link individual cells together into a functional unit

Question 21

name the three types of intercellular junctions and their function

Answer 21

-occluding
seal intercellular space in-between two cells, ie prevents diffusion
AKA- tight junctions or zonula occludens

-anchoring
1. adherent junctions: so they link submembrane actin bundles from cells that are next to eachother together
AKA zonula adherens
2. macula adherens ie desmosomes , they link submembrane intermediate filaments of adjacent cells - provide mechanical stability

-communicating
ie gap junctions
they allow selective diffusion of molecules between adjacent cells, pores are produced by connexion proteins
*found mostly in epithelial

Question 22

what is a junctional complex

Answer 22

when a bunch of intercellular junctions are found together in certain epithelial tissues

Question 23

how do materials move into and out of the cell

Answer 23

by:

1. diffusion
2. via transport proteins
3. incorporation into vesicles (ie endocytosis and phagocytosis)
   - endocytosis = the cell membrane invaginates, fuses and the newly made endocytotic vesicle - endosome - buds into the cell
   * *exocytosis is the opposite
   - phagocytosis = for larger material ie the bacterium binds to the cell surface receptors which triggers extensions the cell to engulf it forming a phagosome, this will then bind with a lysosome carrying digestive protein, and at this stage the bacterium would be a phagolysosome