Block 2: Lecture 6. cells structure and function Flashcards
What is the main difference between eukaryotic and prokaryotic cells?
Eukaryotic cells have membrane-bound organelles and are much larger
Prokaryote cells lack a membrane-bound nucleus
In prokaryotes DNA is not organised within the membrane to form a nucleus
No internal membranes around organelles
Cytoplasm
everything inside the plasma membrane including the organelles,
but not including the nucleus
Cytosol
The fluid portion of the cytoplasm
water plus dissolved and suspended substances (eg. ions, ATP, proteins, lipids)
Does not include the organelles
major organelles
Nucleus
Endoplasmic Reticulum (smooth and rough)
Golgi apparatus
Lysosomes
Mitochondria (Mitochondria do have a membrane but are not part of the endomembrane system)
Ribosomes(Ribosomes Do not have a membrane)
The Endomembrane system
Nuclear envelope Endoplasmic Reticulum (smooth and rough) Golgi apparatus Lysosomes vesicles plasma membrane
Plasma membrane structure
double layer of phospholipids with embedded proteins
Phosphoheads face the outside to the intracellular or intercellular liquid and the lipid tales are connected to each other on the inside
Much of our body is hydrophilic or “water loving”
Fats in cell membrane provide a barrier to water
Phospholipid
Phospholipids are molecules with hydrophilic phosphate heads and hydrophobic lipid tails. They comprise cellular membranes, regulate certain cellular processes, and possess both stabilizing and dynamic qualities that can aid in drug delivery.
(lysosome consists of phospholipids)
amphipathic means
have both hydrophilic and hydrophobic regions.
Plasma membrane proteins
Integral proteins(embedded partially or fully into the membrane) eg Transmembrane protein( contact extracellular and cytoplasmic areas)
peripheral membrane proteins( can respond to receptor molecule change)
Functions of plasma membrane proteins
(a) Transport(channels, transporters, general or selective, gated/not gated
(b) Enzymes. Carry out chemical reaction, specific shape interaction.
(c)Signal transduction
(Receptors .Signal transduction.
A signaling molecule will bind and will cause a change on the inside if the cell, pass a signal from the outside to the inside. Not moving the molecule, transduction and change in shape of the other side of the protein.)
(d)Cell-to-Cell recognition
Use of glycoproteins (carbohydrate + protein) as molecular signatures of the extracellular side of the cell
(e) Intercellular joining( junctions)
(f) Attachment to the cytoskeleton and ECM. eg. Fibronectin mediates contact between cell surface integrins and ECM(collagen). Inside the cell is linked to the outside of the cell–> enables movement
cell specific & cell dynamic
Cell specific:
Not all cells have the same job. Protein are different in different cell types. Eg. Neurotransmitter/transport protein in the brain
Dynamic:
Even within the same time they will be responding to different conditions at that time.(influx of signal–> change in the protein representation on the outside of the cell)
Nucleus structure
Enclosed by double lipid bilayer called nuclear envelope, continuous with rough ER
Entry and exit through nuclear pores
Chromatin(DNA and protein)
Nucleus function
-rRNA production( assembly of small and large units of ribosomes)( in the NUCLEOLUS)
- protect DNA in eukaryotic cells
- pores regulate movement of substances( eg protein and mRNA)
- molecule segregation to allow temporal and spatial control of cell function
How is DNA packed in the Nucleus
DNA wrapped 2x around group of 8 histones, to form nucleosomes collectively known as chromatin
As cell prepares for cell division, chromatin condenses further to chromatin fiber then condenses further into loops then stacks as chromosomes.
How is DNA packed in the Nucleus
DNA wrapped 2x around group of 8 histones, to form nucleosomes collectively known as chromatin
As cell prepares for cell division, chromatin condenses further to chromatin fiber then condenses further into loops then stacks as chromosomes.
Gene
a DNA segment that contributes to phenotype/function
Size of cell and nucleus
cell: 10-20 microns
nucleus: 5-6 microns
What stage is the cell in most of the time
interphase
easier for transcription to happen/access to DNA
ribosome function
protein production
Where translation occurs( from mRNA)
2 sites of ribosomal protein production in the cell
free in the cytoplasm making proteins to be used in cytosol (non-endomembrane destinations)
OR
attached to the RER - making non-cytosolic proteins/endomembrane
Ribosome structure
large and small subunit
large-where translation occurs
made out rRNA
subunits are assembled in nucleolus and leave through nuclear pores
Endoplasmic reticulum
an extensive network of tubes and tubules, stretching out from the nuclear membrane
2 types of endoplasmic reticulum
rough( with ribosomes)
and smooth
lumen inside
Rough endoplasmic reticulum
The major function is the production of:
• Secretory proteins
• Membrane proteins
• Organelle proteins
proteins enter the lumen within the rough ER for folding
Rough ER membrane surrounds the protein to form
transport vesicles destined for the Golgi
*most secretory proteins are glycoproteins. The carbohydrates are attached to the proteins in the ER by enzymes built into the ER membrane.
Smooth endoplasmic reticulum
extends from rough ER
Lacks ribosomes: doesn’t make proteins
The major function is as a housing unit for proteins and enzymes
Synthesizes lipids, including steroids and phospholipids
Metabolism of carbohydrates
Storage of cell-specific proteins, not all cells make all proteins
(Examples:
Liver: houses enzymes for detoxification(drugs and poisons) and for glucose release Muscle: calcium ions )
Functions are tissue-specific
golgi apparatus structure
made up of 3-20 flattened membranous sacs called cisternae, stacked on top of one another (“pita bread”)
trans- “shipping side of Golgi)
cis-“receiving side of Golgi”
*cisternal maturation- the cisternae progress forward from the cis to trans face carrying and modifying the cargo as they move.
golgi apparatus function
Functions:
modify, sort, package and transport proteins received from the rough ER using enzymes in each cisternae
Modifications occur within each sac
(formation of glycoproteins, glycolipids and lipoproteins)
Formation of:
• secretory vesicles (proteins for exocytosis)
• membrane vesicles (PM molecules)
• transport vesicles (molecules to lysosome)
Lysosomes features and functions
vesicles formed from golgi membrane
membrane proteins pump H+ in to maintain acidic pH inside the lysosome
Main function is digestion of:
• substances that enter a cell
• cell components e.g. organelles - autophagy
• entire cells - autolysis
Mitochondria structure
Mitochondria are made up of:
• Outer mitochondrial membrane
• Inner mitochondrial membrane, with folds called cristae
• Fluid filled interior cavity, called the mitochondrial matrix
Have their own ribosomes. Have their own genome where they can encode mitochondrial specific products
Mitochondria function
Produce ATP
*The more energy a cell requires, the more ATP it must make, and the greater the number of mitochondria present
Cytoskeleton
Fibres or filaments that help to maintain the size, shape and integrity of the cell:
•Act as scaffolding across the cell
•Involved in intracellular transportation and cell movement
3 types of fibers in cytoskeleton
Microfilaments
Intermediate filaments
Microtubules
(smallest to largest)
Microfilaments(cytoskeleton)
Diameter: 7 nm
Comprised of actin molecules assembled in two long chains, twisted around each other
Found around the periphery and lining the interior of the cell
Function:
Bear tension and weight by anchoring the cytoskeleton to plasma membrane proteins, and promote amoeboid motility if required (eg. macrophage)
Assembled and disassembled as required – they are dynamic(Do not stay the same, the cell will have different amounts of microfilaments)
Cell motility. Especially as a part of the contractile apparatus of muscle cells.(actin thin filaments)
Intermediate filaments(cytoskeleton)
Diameter: 8-12 nm.
Comprised of a diverse range of different materials; one example: is keratin Found in the cytoplasm of the cell.
Function:
• bear tension and weight throughout the cell, e.g., during cell anchoring,
• act as a scaffold for cellular organelles, e.g., the nucleus. Keeps organelles in place.
Usually the most permanent of the cytoskeleton -scaffold does not need to change
Microtubules( cytoskeleton)
Diameter: tubular structure, 25 nm with the central lumen of 15 nm diameter
Comprised of tubulin dimers (alpha and beta), coiled, to form a tube
Extends from centriole into cytoplasm/nucleus
Functions:
• Support cell shape and size
• Guide for movement of organelles,
e.g., vesicles from Golgi to membrane
• Chromosome organization – cell division
• Support and movement of cilia /flagella
Assembled and disassembled as required - are dynamic
nuclear lamina
the netlike lamina lines the inner surface of the nuclear envelope
Give an example of cells that would have large number of ribosomes based on the ribosome function
pancreas( production of enzymes–> high production of proteins needed)
Proteins made in ribosomes in cytosol vs ER
Most of the proteins made on free ribosomes function within the cytosol, e.g enzymes that catalyze the first steps of sugar breakdown.
Bound ribosomes generally make proteins that are destined for insertion into membranes, for packaging within certain organelles such as lysosomes, or export from the cell(secretion).
centrosome
microtubule organizing center. Within the centrosome, there is a pair of centrioles
Before an animal cell divides the centrioles replicate.
where are ribosomal subunits synthesized and assembled?
nucleolus
