The Endomembrane System of Eukaryotes (CH 4.4) Flashcards
What is an Endomembrane?
- Located inside the eukaryotic cell
- Membranes that form an elaborate internal of cell= fills the cell &; divides it into compartments
- Fundamental distinction between prokaryotes & eukayotes
What is the job of the Endomembrane?
- Channels the passage of molecules through interior of cell
- Provides surface for synthesis of lipids &; some proteins
What is the largest internal membrane?
- Endoplasmic Reticulum (ER)= rough & smooth
- ER may also be connected to cytoskeleton= affects ER strucure &; growth
What is the Endoplasmic Reticulum made of?
- Phospholipid bilayer embedded w/ proteins
- Connected from one bit of RER to another bit of RER, one bit of SER to another bit of SER, & Be continuous between SER & RER
What are the 2 largest compartments in Eukaryotic cells?
- Inner region of ER= Cisternal Space/ Lumen
- Outer region of ER= Cytosol= fluid compartment of cytoplasm containing dissolved organic molecules (proteins or ions)
What is the Rough Endoplasmic Reticulum made of &; what is it’s job?
- Flattened sacs
- Surface is covered in ribosomes
- Site for protein synthesis
What happens to the proteins synthesized on RER’s surface?
- Destined to export from cell
- Sent to Lysosomes, Vacuoles, or embedded in Plasma Membrane
- Enter Cisternal Space= 1st step of sorting proteins to their destinations
What does the sequence of the protein being synthesized determine?
-Whether the ribosome will become associated w/ ER or remain a cytoplasmic ribosome
What happens to newly synthesized proteins in ER?
- Can be modified by the addition of short-chain carbos to form Glycoproteins=
- Destined for secretion &; separated from other products & then packaged to be sent go Golgi Apparatus for further modification & transport to other locations
What makes up the Smooth Endoplasmic Reticulum?
- Variety of structures
- Network of tubules, higher order tubular arrays
What does the membranes of SER contain?
- Embedded enzymes
- Involved in synthesis of variety of carbos & lipids
- Membrane lipids are assembled & sent to wherever they need membrane components
- Membrane proteins are in plasma membrane are inserted by ribosomes on the RER
What are the important functions of SER?
- Store intracellular Ca2+= keeps cytoplasmic level low which allows Ca2+ to be used as a signaling molecule
- Modification of foreign substances to make them less toxic (enzymes in liver carrying out detoxification by neutralizing peniclliin, etc)
What does the ratio of SER & RER depend on?
- Cells function
- Cells that carry out extensive lipid synthesis (testes, intestine, brain= more SER
- Cells that synthesize proteins that are secreted= more RER
What is the Golgi Apparatus/ Body made of?
- Flattened stacks of membranes
- Individual stacks= Cisternae & vary in # within Golgi body
What is a Golgi Ribbon?
- Individual Golgi that are linked together
- Abundant in Glandular Cells (manufacture & secrete substances)
What is the Golgi’s job?
- Collection, packing, distribution of molecles synthesized at one location &; used at another within cell/outside it
- Synthesis for cell wall components & sent to plasma membrane
What is the front & back portions of the Golgi for?
- The front= receiving end= Cis Face located near ER
- The back= Exporting= Trans Face
What occurs in the Cis Face & Trans face of the Golgi?
- Material arrives in transport vesicles in the Cis Face
- Material exits via Trans Face where they are discharged in secretory vesicles
How does material transmit through the Golgi?
-Maturation of Cisternae from Cis to Trans
What happens to proteins & lipids manufacured on SER & RER?
- Modified as they pass through Golgi
- Common alternation= addition/ modification of short sugar chains= Glycoproteins & Glycolipids
How do the enzymes in Golgi modify EXISTING Glycoproteins & Glycolipids?
- Cleaving a sugar from the chain
- Modifiying one or more of their sugars
What are Lysosomes?
- Formed from vesicles budding off of Golgi
- Contain high level of Hydrolytic (degrading) enzymes= catalyzes rapid break down of proteins, nucleic acids, lipids, & carbos
- Elimnate other cells that the cell has engulfed by Phagocytosis
How are Lysosomes & their digestive enzymes activated?
- Fusing w/ food vesicle produced by Phagocytosis
- Or by fusing w/ an old/ worn-out organelle
- Fusion activates proton pumps in lysosomal membrane= low pH= Lysosomal digestive enzymes are activated= degredation of macromolecules in food V/ old organelles
Why are the accumulations of Glycolipid in Lysosomes bad?
-Affects nerve cell function= variety of symptoms like seizure & muscle regidity
What are Microbodies?
- Diverse category of organelles
- Variety of enzyme-bearing membrane enclosed vesicles
- Found in plants, animals, protists
- Distribution of enzymes into microbodies= principle way eukaryotic cells organize their metabolism
What is Perixisome?
- Important microbody= contains digestive & detoxifying enzymes that produce hydrogen perooxide as a by-product
- Contain enzyme catalase which breaks down hydrogen peroxide into water & oxygen
How do Perixomes form?
-From the fusion of ER-derived vesicles= important Perixsomal proteins to form a mature Perixsome
What are Vacuoles?
- Located in Plants
- Membrane-bounded structure
- Stores dissolved subtances & can expand in size to increase tonocity of plan cell
- Kinds & # of vacuoles in cell depends on it’s particular needs
What is the Tonoplast?
- Membrane surrounding vacuole
- Contains channels for water that help maintain its tonocity/ osmotic balance= allows cell to expand & contract depending on conditions
What is the structure of a nucleus?
- Surrounded by nuclear envelope= double membrane connected to each other (each membrane is one lipid bilayer w/ other components)
- Has Inner & Outer bilayer
- Has Nuclear Pores
What does the Inner bilayer of a Nucleus have?
-Special proteins connected to Nuclear Lamina= associated w/ functions inside the nucleus (expression of genes, replication)
What does the Outer bilayer of a Nucleus have?
- Ribosomes & connected to RER
- Associated w/ functions outside the nucleus (cytoplasm)
How many bilayers does a molecule have to go through to reach the nucleus?
3 bilayers
- Plasma membrane
- Outer Nuclear Envelope
- Inner Nucler Envelope
What are the 3 functions of the Nucleus?
- Contains & protects genetic info long term
- Expression of genetic info
- Determines which part of genetic info should be expressed @ which time & which cells
What kind of genetic info does the nucleus protect?
- It protects the info of Somatic cells for a lifetime (Non sperm/ egg cells) bc damage to somatic cell can cause cancer
- Its effective storage in germ-line cells bc if DNA is damaged then mutations can be passed down to generation
How does the Nucleus express genetic info?
-Starts w/ transcription (DNA is copied into new RNA & then that RNA leaves via nuclear pore)
How is Eukaryotic DNA organized?
-Linear double-stranded DNA= chromosomes
What is Chromatin?
- The stuff of chromosomes
- Includes noncovalently attached proteins (Histones) that protect & regulate DNA
- Histones wrapped around DNA molecules into coils which are then further wrapped & condensed into chromosomes
What do Chromosomes contain?
- Genetic material DNA
- RNA that was made by transcription
What are the 2 types of Chromatin?
- Euchromatin
- Heterochromatin
What is Euchromatin?
- DNA being actively transcribed
- Also contains DNA that IS actively being expressed
What is Heterchromatin?
- Contains DNA thats NOT actively being transcribed
- DNA not being expressed at that particular time
How is DNA organized in the nucleus?
- Specifically organized in the nucleus
- Chromosomes occupy separate volumes= territories
- Some genes are also in particular places relative to genes
- Location of euchromatin & heterchromatin is part of that organization
What is the Nucleolus?
- Special region within the nucleus
- Site of transcription in RNA components for ribosomes
- Site of Ribosomal assembly (RNA + protein from cytoplasm)
What is the Nuclear Lamina?
-Mesh of polypeptides
Where is the Nuclear Lamina located?
-On inner surface of inner membrane is connected to inner membrane of nuclear envelope
What is the Nuclear Matrix?
-2nd mesh of polypeptides
Where is the Nuclear Matrix located?
-Throughout internal volume of nucleus
What is the structure for Ribosomes?
- Large complex of noncovalently associated ribosomal RNA & protein assembled in Nucleolus
- Some are free-floating in nucleus & other are attached to RER
- 5 different molecules/ rRNA & more than 50 protein components
- Have large & small units (large stays large, small stays small)
What is the function of Ribosomes?
- Site where mRNA directs protein synthesis
- Makes covalent bonds (amide/peptide) that links w/ amino acid= made by dehydration synthesis & catalyzed by rRNA component
What is mRNA?
-Subset thats copied from DNA in euchromatin= the sequence that determines the sequence of amino acids in polypeptides that are made on ribosomes
What is rRNA?
-Speeds up a reaction that is normally very slow (formation of peptide bonds via DHR)= has large activation energy
What is the order for Protein Synthesis?
- mRNA transcribed in nucleus in Euchromatin
- mRNA exits via Nuclear pore
- mRNA meets small subunit joined by large subunit
- mRNA is translated into protein
Why are proteins important?
-Their sequnce determines structure & that structure determines function
What is the central dogma of molecular biology?
-DNA–>RNA–> PROTIEN
What are Vesicles?
-Small spherical sacs of membrane for transport between compartments
What do Vesicles do?
- Contains proteins, & other materials like membrane components , P.lipids & other molecules
- Move around cell & “budd off” ER or Golgi to go to another compartment
- Can have different names depending on origin & destination (can be called transport, lysosomal, secretory)
What is the pathway for Protein Secretion?
- Start inside RER
- Then in transport vesicle
- Then inside sacs of Cis Face golgi
- Then inside sacss of Trans Face golgi
- Then inside secretory vesicles
- Then these vesicles fuse w/ plasma membrane which releases the contents that are inside the vesicle into the extracellular space where they diffuse away
What is Exocytosis?
-When secretory vesicles fuse w/ plasma membrane
How are antibodies secreted into extracellular space?
- By plasma cells
- ABS= made on RER & then travel to golgi in vesicles where they are sorted, modified, etc
What is the pathway for Membrane proteins?
-Similar to the pathway for protein secretion except that they are partly in the ER lumen during exocytosis
What is the pathway for proteins destined to be organelles?
-The same as protein synthesis EXCEPT that vesicles leaving the golgi are either becoming organelles themselves (maturing) OR gonna fuse w/ existing organelles to deliver their protein cargo to it
