Lecture 8: Cell Size and Endomembrane Flashcards
Why are cells so small?
-Just waving your arm requires many diffusion process, therefore they must occur on a millisecond scale
-Diffusion is only effective over ver small distances(distance traveled by a defusing molecule is proportional to the square root of time)
-Cells need to be small as it would take way to long for things to diffuse across the membrane
How many cell are found in the human body?
Around 40 trillion
Why can eggs be big?
Because all they do is store stuff
What are prokaryotes?
-Single-celled organism
-Consists of archea and bacteria
Characteristics of prokaryotes?(4)
- Extremely small(same size as an organelle)
- Prokaryotes can live in any environment(they can eat anything(plastic))
- Their DNA sits in a nucleoid not surrounded by a membrane
- Do not have a nucleus
Characteristics of eukaryotes?(4)
- Have a membrane enclosed nucleus that contains DNA (enclosed by a nuclear envelope that consists of two membranes)
- Have organelles enclosed by membranes
- Larger than prokaryotes
- Compartmentalization
Why are eukaryotes so much bigger than prokaryotes?
Due to compartmentalization
What is compartmentalization and why does it make eukaryotes big?
Many internal membrane systems that create very small specialized spaces where diffusion can occur very quickly
Parts found in prokaryotes(4)?
- Plasmid(circular DNA)
- Cell Wall: Provides stability and structure
- Ribosomes: Translate proteins
- Nucleoid: Filled with DNA and proteins
Metabolism of prokaryotes
Prokaryotes can eat anything
- Can use all kinds of different final electron acceptors
Explains why bacteria are found EVERYWHERE
Eukaryotes and metabolism
-Can only use oxygen as the final electron acceptor
-Must eat other plants/animals to survive
Plant cell characteristics
- Rigid cell wall made up of cellulose
- No sodium potassium ATPase(it is unique to animals), plants don’t need osmolarity regulation because they have a rigid cell wall and water can just flow in.
- Modified lysosome called a vacuole
- Chloroplasts
What is the endomembrane system?
Group of membranes and organelles within eukaryotic cells that work together
Compartmentalization and the end-membrane system gives rise to organelles. Name some of the organelles.
- Nucleus
- ER
- Golgi
- Vesicles
- Lysosomes
What organelle does the outer membrane of the nucleus touch?
The ER
Role of vesicles?
To communicate with the cell membrane and between the Golgi and ER
What is the lumen(interior) of the Golgi, vesicles and ER made of?
Extracellular space
Does every cell in the body have the same umber of each organelle?
NO, each cell type has a different ratio of these organelles depending the specialized function they have
ex. Pancreas cells have a lot of RER to make digestive enzymes
What is found in the nucleus?
The nucleus contains DNA stored as chromosomes and it also contains proteins
What is the nucleolus?
This is where ribosomes are assembled from rRNAs
-Assembled ribosomes are then transported through the nuclear port to the cytoplasm
What occurs in the nucleus?
-DNA is replicated
- DNA is transcribed into mRNA or rRNA by RNA polymerase
What are nuclear pores and their functions?
Holes in the nucleus that allow the transport of stuff in and out of the nucleus
Where are ribosomes found in regards to the ER?
Ribosomes are found just on the outside of the ER, never on the inside
Where is the rough endoplasmic reticulum?
Close to the nucleus, its membrane touches the nuclear envelope surrounding the nucleus
Why is it called the rough ER?
Due to the ribosomes attached to the outside of the ER membrane
How do ribosomes translate proteins on the RER?
Ribosomes bind to the outside of the RER when they start translating a membrane protein
The first few amino acids of the protein encode a signal that tells the ribosome to bind to the RER
-The freshly made protein is then inserted into the RER membrane and later into the lumen of the RER
What occurs in the SER?
-All lipids are made in the SER
-Detoxification also occurs in the SER (oxidation)
ex. adding hydroxylgroups that make a molecule more hydrophilic, such that it can be excreted
Who has a lot of SER?
DRUGGIES(need em to detoxify)
What is the Golgi?
Stack of membranes that helps process and package proteins and lipid molecules
What happens to proteins after they leave the ER?
Proteins are transported from the ER to the cis side of Golgi with the help of vesicles, the proteins then go through the Golgi (as they do so they are modified). After going through the Golgi the protein filled vesicles break off the Golgi on the trans side and are then moved to different destinations
How do proteins and lipids flow through the Golgi?
From the cis side to the trans side
What did the pulse chase experiment show?
How proteins travel through the end-membrane system
How did the pulse-chase experiment work?
Radioactive amino acids are added to a culture and radioactive proteins will show up in the RER, later the Golgi, secretory vesicles and eventually the extracellular fluid
What is the path of a protein through the endomembrane system?
RER – Vesicles — Golgi — Vesicles – Extracellular fluid
What is phagocytosis?
Phagocytosis: Large particles such as microorganisms and dead cells are ingested via large endocytic vesicles called phagosomes
What is endocytosis?
Process by which cells engulf large molecules.
1. Particles come in contact will cell
2. Cell membrane wraps around the particle
3. Once the particle is surrounded the vesicle break off into the cell(endosome)
4.This vesicle now may fuse with other vesicles
5. The endosome will then become a lysosome with a low pH its contents are digest and then released to the cytosol
What is autophagy?
Self-eating
- Lysosomal organelles can surround entire organelles and chunks of cytoskeleton and digest them
What is a lysosome?
Organelle that contains digestive enzymes
What makes sure that proteins end up in the correct spot after exiting the Golgi?
The primary amino acid sequences on proteins indicate where each one must go after it exists the Golgi in a vesicle
