Wk2 Lecture 2 Ch 7.2, 7.4. 7.5, 7.6 Flashcards
How many membranes does the nuclear envelope have?
2, each consists of a lipid bilayer
Is the nuclear envelope continuous or separated from the Endoplasmic Reticulum?
Continuous
What is the nuclear lamina?
A lattice-like sheet of fibrous proteins that surrounds the surface of the nucleus under the nuclear envelope
What does the nuclear lamina do?
-Maintains shape of membrane by stiffening its structure
-Provides attachment points for each chromosome
What is the nuclear pore complex?
Consists of nuclear pores (made up of 30 proteins), which function as very big doors/gates into and out of the nucleus
What is exported to the cytoplasm from the nucleus?
-mRNA
-ribosomes
Where are mRNA and rRNA/ribosomes synthesized? What is each item’s purpose?
In the nucleus; ribosomal RNAs are manufactured in nucleolus to form ribosomes, and mRNA carries info to manufacture proteins.
What is imported to the nucleus?
-Proteins for copying DNA, synthesizing RNA, or assembling ribosomes
-DNA/RNA building blocks
How do proteins and other large molecules enter the nucleus? Does that process take energy?
Nuclear localization signals - think IDs and bouncers; yes, it is an energy-demanding process
How are proteins produced?
- Synthesis of mRNA from DNA occurs in the nucleus
- mRNA moves to cytoplasm via nuclear pores
- Protein synthesized by ribosome from mRNA code
i.e. Central dogma (DNA -> RNA -> Protein)
What is the ER signal sequence?
A signal made by a free ribosome that guides growing proteins (destined for secretion/embedded in membranes) + associated ribosome to the rough ER. Present in the first 20 amino acid residues and is removed when protein synthesis is complete.
What is the SRP (signal recognition particle)?
A complex of RNA and protein that binds to the ER signal sequence (causing protein synthesis to stop.
How do proteins enter the endomembrane system?
- Protein synthesis begins on free ribosome, which synthesizes ER signal sequence using mRNA
- ER signal sequence binds to SRP, which stops protein synthesis
- Ribosome + ER signal sequence + SRP complex move to rough ER membrane, where it attaches to SRP receptor
- Receptor and SRP connect => SRP released and protein synthesis continues through a translocon channel
- Growing protein is fed into ER lumen or remain associated w/ membrane as integral membrane proteins, and ER signal sequence is removed
How are proteins transported in the endomembrane system?
- Ribosome deposits protein in ER
- Protein exits ER via vesicle made from ER membrane towards cis face of Golgi
- Protein enters Golgi for processing/further modifications
- Protein exits Golgi via vesicle from trans face towards plasma membrane
- Protein secreted from cell
What is the endoplasmic reticulum a site of?
Site of synthesis (proteins and lipids), processing, and storage (calcium storage in smooth ER)
What is glycosylation?
The addition of one or more carbohydrate groups to a molecule
What is a glycoprotein?
Any protein w/ one or more covalently bonded carbohydrates
What is the purpose of carbohydrates on a glycoprotein?
They change structure as the proteins are folded, which indicates shipment to the Golgi
What is the Golgi Apparatus a site of?
Protein processing, sorting, and shipping
How are products shipped from Golgi Apparatus?
Each protein that leaves Golgi has a molecular tag => tag places protein in a particular type of transport vesicle => allows proteins to be shipped to compartments where they function
- Proteins are tagged
- Proteins are sorted
- Vesicles bud
- Proteins interact with receptors
- Delivery
What is mannose-6-phosphate?
A tag on lysosome-bound proteins consisting of a phosphate group attached to a specific sugar on the surface. No mannose-6-phosphate on protein => protein not transported to lysosome
What does the presence of mannose-6-phosphate target proteins to?
Organelles that eventually become lysosomes => endosomes
What are proteins in vesicles known as?
Cargo
What are vesicles carrying proteins known as?
Trucks
Which cells have lysosomes?
Animal cells
What are lysosomes?
Recycling centers (digestion and waste processing)
What are the three methods of directing material to the lysosome for recycling?
- Receptor mediated endocytosis
- Autophagy
- Phagocytosis
What is pinocytosis?
The ingestion of extracellular fluid into cell via budding of small vesicles from plasma membrane.
Describe steps of receptor mediated endocytosis (forming a lysosome)
- Macromolecules from outside cell bind to receptors
- Endocytic vesicle forms
- Endocytic vescile fuses with early endosome (organelle); proton pumps lower pH
- Increasing acidity of early endosome causes it to mature into the late endosome, which is the pre-lysosomal compartment.
- Acid hydrolases (digestive enzymes) are dropped off by vesicles from the Golgi
- Late endosome => lysosome, which digests the macromolecules
How is cellular (intra and extra) material recycled in the lysosome?
Autophagy and phagocystosis
Describe steps of autophagy
- Damaged organelles are enclosed within an internal membrane called the autophagosome
- Autophagosome is delivered to lysosome and fuses with it
- Components of organelle are digested and recycled
Describe steps of phagocytosis
- Detection-plasma membrane of a cell surrounds a smaller cell/food particle
- Plasma membrane engulfs it, creating a phagosome
- Phagosome delivered to lysosome
- Phagosome is digested and small molecules recycled
Common result of all lysosomal digestion/recycling?
Molecules are hydrolyzed and the products are transported across the lysosomal membrane into the cytosol for recycling.
What is the cytoskeleton?
A dense and complex network of fibers that help maintain cell shape by providing structural support
Is the cytoskeleton static or dynamic?
Dynamic
What do the fibrous proteins of the cytoskeleton do?
- Alter the cell’s shape
- Shift its contents (like train tracks)
- Even move the cell itself (ex: organelles like the mitochondria)
What are the three major types of cytoskeletal elements in eukaryotic cells?
- Actin filaments
- Intermediate filaments
- Microtubules
What are actin filaments?
-The smallest cytoskeletal elements formed by polymerization of individual actin molecules
-Grouped together into long bundles or dense networks
-Have positive and negative ends
Where are actin/micro filaments usually found?
Just inside plasma membrane
Actin/micro filaments are structures that…
Help define the cell’s shape
Actin function
-Structural support
-Movement
What is myosin?
A motor protein- converts chemical energy from ATP into kinetic energy
How does actin work with myosin?
Actin is the rope, and myosin is the ratchet that attaches to it and moves (pulls), making the actin filament slide (sailor pulling rope)
What direction does myosin pull towards?
Negative to positive end of actin filament
What cell movements are caused by the ATP-powered interaction b/t actin and myosin?
CYTOKINESIS (final stage of cell division to form two cells) and CYTOPLASMIC STREAMING (directed flow of cytosol and organelles within plant and fungal cells)
What are intermediate filaments?
A long fiber composed of one of various proteins used for structural support (not involved in movement); no polar ends
What are intermediate filaments defined by?
Size (not composition)
Most familiar intermediate filament?
Keratin (make up skin, hair, nails, and line surfaces inside body) and Nuclear Lamins (make up nuclear lamina layer)
What are microtubules?
Paths of the cell; large hollow tubes made of tubulin dimers (alpha and beta tubulin [polypeptides])
What does the polarity of a microtubule mean?
It has direction
Why are microtubules polar?
They have plus and minus ends
Which tubulin is at each end of a microtubule?
alpha tubulin is at minus end
beta tubulin is at plus end
Which end do microtubules grow from? (faster)
Their plus ends (grow faster)
Where do microtubules originate from?
The microtubule organizing center; plus ends of microtubules grow from MTOC, radiating throughout cell
What is the MTOC of an animal cell called? What is it made of?
Centrosome; consist of two bundles of microtubules, called centrioles, surrounded by shapeless matrix of proteins that help initiate growth of new microtubules
Microtubule function
-Stability
-Involved in movement
-Provides structural framework for organelles
-Railroad tracks (transport vesicles move through the cell along these tracks in energy dependent process)
What is kinesin?
A motor protein with a head region that binds to the microtubule and a tail region that binds to the transport vesicle
How does kinesin allow for movement of vesicles towards the plus end along microtubules during transport from trans-Golgi to plasma membrane?
The domains (microtubule and transport vesicle) it binds to allow it to “walk” along the microtubule through a series of conformational changes (as it hydrolyzes ATP); moves towards plus end of microtubules
What are flagella?
Long, hairlike projections from the cell surface that move cells
Eukaryotic v Prokaryotic flagella
EUKARYOTIC:
-consists of several microtubules
-surrounded by plasma membrane
-whiplike movement
PROKARYOTIC:
-consists of single helical rod
-not surrounded by plasma membrane
-propellor-like movement
What are cilia?
Short, filament like projections that help move cell and circulate fluid/particles around surface of stationary cell
What is the axoneme of cilia and flagella?
A complex “9+2” arrangement of microtubules connected by links and spokes that describes the anatomical structure of cilia and flagella.
What does “9+2” arrangement of the axoneme mean?
The axoneme has 9 microtubule doublets (pairs) surrounding two central microtubules
What is the basal body?
Identical in structure to a centriole (9 microtubule triplets arranged in a circle) and serves as an MTOC for growth of the axoneme doublets
What is dynein?
A motor protein that forms the arms between doublets => hydrolyzed ATP causes bending (of cilia or flagella)
Changes shape when ATP is hydrolyzed to “walk” up the microtubule => shape changes move dynein towards minus end
What are the 4 major types of organic molecules/macromolecules?
- Carbohydrates
- Lipids
- Proteins
- Nucleic Acids
What are the 2 main reactions for building and breaking down of molecules?
- Synthesis - anabolic
- Decomposition - catabolic
When does synthesis occur?
Occurs when atoms, ions, or molecules combine to form new, larger molecules
What is anabolism?
Synthesis of molecules in a cell
When does decomposition occur?
Occurs when a molecule is split into smaller molecules, ions, or atoms
What is catabolism?
Decomposition reactions in a cell
What is dehydration synthesis?
Monomers covalently bond together to form a polymer through the removal of a water molecule (think sticky part of enelope) - hydroxyl removed from one monomer, hydrogen from the next
What is hydrolysis?
Splitting a polymer (lysis) by the addition of water (hydro) - a covalent bond is broken
