Cells and organelles

Question 1

Cell discovered in 1665 by robert hooke, not much known about him as isaac newton stole his thunder

Question 2

1839 Cell theory

Answer 2

All organisms consist of one or more cells • The cell is the basic unit of structure for all organisms (Thought cells originated “spontaneously”)

• theodor schwaan

Question 3

1855 cell theory and human mechanisms ( pathology )

Answer 3

The cell was the basic unit of the body that had to be studied to understand disease • Cells originate from preexisting cells - start of thoery of mitsosi and meoisis

Rudolf Virchow

Question 4

The size of cells ensure that they can have adequate diffusion and be able to move around the body freely , also ensures that if damage occurs it is not the end of the world. All cells are smaller than the eye . Some cells can be much smaller ( eg bacteria ) or larger ( human eggs )

Question 5

Properties of cells

Answer 5

Microscopic packages tha ac as independent units

cells originate from preexisting cells - grow and reproduce

cells have a finite lifetime - they do die - by deisng, age , disease

Cells internal processes allow them to change / adapt / respond

Different jobs for diff cells/ parts of the body

Question 6

Membranes enclose the cell space

Answer 6

The plasma membrane encloses the cell

as packages of life cells can function as ind units because they are enclosed by a semipermeable membrane ( flexible, continous bag - a barrier to water )

The plasma membrane encloses the cell as an independent reaction container ( contains salty, protein rich solution )

The membrane is composed of a bilayer of phospholipid molecules with added protein molecules

The lipid bilayer is 5nm long

The protein molecules are typically 50% of the mass

Reading

• all proteins are funadmentally the same in overall structure

the membranes differ because of protein/lipid types

1/3 of all cell proteins are membrane proteins

Proteins define function - receptors, transporters, signalling,adhesion etc

Question 7

There are two different types of cells

Answer 7

Prokaryotes - before a nucleus - only one outer membrane

the simplest and smallest prokrayotes are bacteria ( all processes in cytosol , no internal membranes, nucleus absent )

Up to few thousands of a mm ( few microns ) in size

Amongst “ oldest “ and most abundant type of life of earth ( preceded complex cells )

Question 8

Eukaryotes

Answer 8

some cells have internal membranes and are bigger

more complex eukaryotes are found in human, animal and plants

( cytoplasm divided by membrane to enclose compartments/organelles )

Up to a 10 thousandths of a mm in size ( 10 microns or much more )

Amongst more recent in evolution representing complex cells in multicellular organisms

eukarytes are much bigger than prokaryotes

a skin cell infected with bacteria

Question 9

Eukaryote protein expression

Answer 9

• DNA (with its genes) packaged in a central store called a nucleus. Specifically in EUKARYOTIC CELLS: (human, animal, plant cells) • Nucleus is enclosed by a double membrane the nuclear envelope (nucleus is one of a number of cell compartments) • mRNA (message) passes from the nucleoplasm to the cytoplasm via holes called nuclear pores Protein expression – the organelles • mRNA is decoded and proteins made (translation) on specialised factories ribosomes • DNA (with its genes) transcribed to produce mRNA (transcription)

DNA is packaged with proteins called histones – forming a complex called chromatin

Chromatin is packaged in two main ways – euchromatin and more dense heterochromatin

Most of the active genes are found in the euchromatin, inactive ones in heterochromatin

Nuclear pores are selective aqueous channels for transport between nucleus and cytosol (mRNA passage but also proteins in both directions)

nuclear pores - openings in the nucleus for mrna

euchromatin - lighter

heterochromatin - darker

Question 10

mRNA and translation machinery - ribosomes in the cytoplasm in eukaryotes

Proteins are made on specialised organelles called Ribosomes Many ribosomes remain “free” during protein translation Ribosomes have two subunits Ribosomes decode mRNA message and convert it to linear polypeptides (protein)

Big decisions are made for ribosomes as they start protein synthesis - they basically have to determine what that protein is destined to be , whether its a cytoplasm or nuclear protein or destined to have further werk done in the rer and golgi

All protein synthesis starts in the cytosol

First stretches of any proteins destined for ER/ golgi processing are recognised and then bound to ER to generate ER coated with ribosomes - RER

Question 11

Free ribsomes

Answer 11

Free ribosomes (translating proteins destined for cytosol, nucleus, mitochondria

Question 12

Bound ribosomes

Answer 12

Bound ribosomes (these ribosomes are translating proteins with signal sequences destined for RER and other membranes and secretion)

Question 13

Eukaryote secretion

Answer 13

Pathway for secretion

synthesis modification secretion delivery

RER -> Golgi -> secretion/plasma membrane

Vesicles vesicles

Vesicles carry cargo from RER to the golgi

cargo processed and sorted in the golgi

vesicles bud from the golgi with membrane for the PM ( constitutive vesicles )

Different vesicles can bud from the golgi containing packaged secretion

Question 14

RER function

Answer 14

(1) Site of membrane synthesis (lipids and proteins) (2) Modifies proteins – adds sugar chains, trims them (3) Quality control – e.g. monitors correct folding (4) Signals stress - e.g. when secretion is blocked/poorly folded proteins

Question 15

The rer to the golgi in eukaryote secretion

Answer 15

• RER makes membrane and is widely spread through most cells • Cargo packaged into vesicles sent along tracks to the central Golgi complex • Golgi complex stacks of flattened sacs (found close to the nucleus). • Golgi receives these membrane vesicles + their content (cargo) from RER.

Question 16

Golgi

Answer 16

All membrane exported from the ER goes through a processing factory called the golgi

Processes and sorts cargo into vesicles specific for the target organelle (cell membrane, lysosome, outside of the cell (secretion))

Question 17

Golgis function

Answer 17

(1) Receives output of RER (2) Modifies lipids/proteins – grows sugar chains on proteins/adds phosphate to some proteins (1) Sorts and packages cargo into distinct vesicles for export to other organelles (this happens at the exit face of the Golgi)

Question 18

How is vesicle content released and membrane added to the plasma membrane ?

Answer 18

Secretory vesicles - release content via exocytosis at the plasma membrane

The vesicles move toward and way from the golgi through slight polarisation on microtubules that are 25 nm thick , they ahve a motor protein on them That has the vesicle cargo on top

Most of the microtuules emanate from the centrosome,which the golig is normally close to int he cell centre, and other organelles may move or be positioned on the microtubules

the centrosome is the centre for organising microtubules and it usually contains two centrioles and 0 array of microtubules

Question 19

Uptake and degradation in eukaryotes

Answer 19

Lyosomes are low ph degenerative bodies that contain hydrolytic enzymes which degredate the material.

Uptake is by endocytosis ( large particles by phagocytosis and molcules by pinocytosis )

membrane/ cargo internalised delivered to endosomes and then passed to lyosomes for degradation. Some membrane is reycled back to the cell surface

portions of the cell itself can be walled off and digested in lyosomes ( autphagy ).

Phagocytosis ( big chonks ) , pino cytosis ( cell drinking )

receptor mediated endocytosis is very effective bc it has selective uptake

Endocytosis ( uptake for degradation to lyosomes; uptake for recycling )

Question 20

Membrane and functional components of lyosomes and endosomes are also made on RER

• proteins must be diverted by special sequences ( sorted from secretory pathway) in the golgi

SO membane of RER, golgi , secretory vesicles , PM, lyosomes and endosomes all made in the RER

Question 21

Degradation can happen in the cytosol without mebranes ( lyosomes )

Degradation by a proteosome

Answer 21

• “Junk” protein is tagged (with ubiquitin) • No membrane involved • Macromolecular complex • In the cytoplasm not in lysosomes - turns it into fragments

kind of like a bin bag

Question 22

Two great steps in eukaryote cell evolution

compartmenalization and mitochondria

Answer 22

Compartmentalization

internal membrane compartments with a range of specilaised functions

this means that specialised rwactions that can sometimes be harmful can be seperated and concentrated and optimised while not damaging other parts of the cell

vesicle transport is a consequence of cargo between compartments - selective transport maintains composition of membrane compartments - vesicle budding - one type of scaffold coat is called clathrin

Mitochondria (Produce most of ATP supply Enabled cells to grow bigger Present in all eukaryotic cells Two membranes - inner membrane folded into interior Contain their own DNA - reproduce by dividing in two All your mitochondria come from your mothers egg (cell nucleus makes most but not all mitochondria proteins))

the best idea -

About 2 billion years ago large non-nucleated cell (archaea) engulfs a bacterium. • Bacterium provides energy (ATP) + multiplies to provide energy boost for growth (bigger cells become viable). • During further evolution cell membrane invaginates to form internal membranes – segregation of protein synthesis on ER. ER coats nucleoid to form nuclear envelope.

Question 23

Cytoskeleton

provides framework for cells and organelles

moving/positionng, supproting , protecting

Answer 23

Microtubules

• thickness of a ribosome (25nm), vesicle tracks, position/move organelles (cell division), dynamic - subunits tubulins

Microfilaments

• thinner than microtubules (7nm), generates contractile forces enabling cells to move, parts of cells to move, cells to contract subunits actin + myosin (motility)

Intermediate filaments

• middle thickness (10nm), strength, support Some in cytoplasm (keratins) some support nuclear envelope (lamins) - keratins, lamins

Question 24

There is two organelles prominent in a few specialised cell types

smooth er

peroxiomes

Answer 24

Smooth ER - connected domain of the RER membrane with no ribosomes and involved in lipid, steroid production and detoxification.

Peroxisomes – break down some fatty acids, synthesis some specialised lipids (e.g. in nervous system). Peroxisomes do oxidative reactions using molecular oxygen. These generate hydrogen peroxide, and excess is broken down with catalase.

Question 25

Prokaryotes summarised

Answer 25

Small, simple cells (relative to eukaryotes) • Size: about 1 µm • No internal membrane-enclosed organelles* • No nucleus • Simple cell division

Question 26

Eukaryotes summarised

Answer 26

• Larger cellular dimensions 5-20 µm diameter (1000x bigger than bacteria) • Internal membranes with specialisation and vesicular transport • Packaged DNA in a nucleus • Contain endosymbiont organelles (mitochondria/chloroplasts)

Question 27

Birth and death of cells

Answer 27

chromatin condenses all together as chromosomes during cell division - packaging protects the genes

it is paritioned by microtubule based movementws by the phase metaphase - the microtubules moves and organises the chromosomes into daughter cells

phases in order - prophase - metaphase - anaphase - telophase - cytokinesis

Cells can die on command - programmed cell death - apoptosis - cell deah between digits

Question 28

Multicelluarity

(1) cell specialisation
(2) adaptations for living together

Answer 28

(1) cell specialisation

DIversity - more than 200 cell types identified in human body - arranged into tissues - 4 basic tissue types - eptihelia - connective tissue - muscle - nervous tissue

Protein expression profile defines the type of cell

• Surrounded by an enclosing membrane (reaction containers)
• Cells are protein factories 20,000 different proteins can be coded from an identical set of genes Patterns of protein expression determine each of 200+ cell types
• Grow (increase in size)
• Divide
• Die (disease (age), design)

All cells are derived from a totipotent stem cell

(2) living together

cell communication

static cells can adhere to each other thru junctions

Tight junctions - seals neughbouring cells together in an epithelial sheet to prvent leakage of molecules between them

adherens junction - joins in actin bundle in one cell to a similar bundle in a neighbouring cell

desmosome - joins the intermediate filaments in one cell to those in a neighbour

gap junction - forms channels that allow small water-soluble molecules , including ions, to pass from cell to cell

hemidesmosome - anchors intermediate filaments in a cell to the basal lamina

selective cell-cell adhesion

Question 29

familial hyperchlosterolemia ( defective uptake of lipoproteins )

Answer 29

• LDL receptors bind LDL (“bad cholesterol”) for uptake – 3 causes for defective uptake of LDL • LDLR is not properly transported from RER to Golgi for expression on cell surface (X) • LDLR bound to LDL does not cluster in endocytic vesicles on plasma membrane (X) • LDLR is not recycled back to the cell surface (X)

Question 30

Examples of mistakes and mishaps in cell biology

All diseases are caused by mistakes at cellular level

Answer 30

Hypercholesterolemia (defective uptake of lipoproteins) • Cystic fibrosis (misfolding of key protein) • Hypertension (defective cell-cell adhesion in the kidney) • Congenital heart defects (errors in cell migration during development) • Muscular dystrophy (defective attachment of the plasma membrane to the cytoskeleton) • Lysosomal storage disease (defective intracellular transport of enzymes) • Food-borne illness (Salmonella, E. coli) • Cancer (errors in cell division, migration, cell polarity, growth, etc) • Ageing