Chapter 3 Cells Flashcards
Prepare for first test
What are the three regions of a cell?
- Plasma Membrane
- Cytoplasm
- Nucleus
What is a cell? And what does cell theory say?
Defining cells is to define life.
Cells are the smallest unit of life.
All life forms contain one or more cells.
Cells only arise from other cells.
What are the functions of the plasma membrane?
Physical barrier - separates cytoplasm from extracellular fluid.
Selectively permeable - determines which substances enter and exit.
Communication - plasma membrane proteins interact with chemical messengers and relay messages to cell interior.
Cell recognition - cell surface carbohydrates (glycocalyx) allow cells to recognize each other.
What is the cytoplasm?
It’s the intracellular fluid packed with organelles.
What is the nucleus?
It’s an organelle that controls cell activities.
What is extracellular fluid?
It is like a nutritious soup which contains amino acids, sugars, fatty acids, regulatory substances and wastes.
Cells extract what they need from our ECF.
What are cellular secretions?
These include: digestive fluids and lubricants (saliva, mucus, and serous fluids).
What is the extracellular matrix?
Cells exist in a composite of polysaccharides and proteins. These molecules self assemble into an organized space where they serve as a “cell glue” that help bind body cells. These are particularly abundant in connective tissues.
What two body components does the plasma membrane separate?
It separates intra- and extracellular fluid.
What is the fluid mosaic model?
It refers to the floating proteins that reside in the lipid bi-layer of the plasma membrane. The are continually moving in the membrane and create a fluid mosaic pattern.
What are the features of phospholipids?
They have hydrophilic heads and hydrophobic tails.
How much of the phospholipid bilayer is comprised of cholesterol, and what is it’s function?
About 20% and it stiffens the bilayer.
What are the roles of cell proteins?
Transport - they may provide a channel across the bilayer for a solute or work as a pump.
Receptors for a signal - they may receive hormones, or be altered by there presence in order to elicit a chemical change.
Enzymatic activity - may catalyze metabolic pathways.
Cell-cell recognition - glycoprotiens serve as identification tags.
Attachment to cytoskeleton and ECM.
Cell to cell joining.
Key features of Tight Cell Junctions…
Interlocking junction proteins.
Impermeable junctions
Form continuous seals around the cell
Prevent molecules from passing between cells.
Key features of Desmosomes…
Formed with linked proteins - cadherins.
Anchoring junctions.
Bind adjacent cells together like molecular velcro.
Help keep cells from tearing apart.
Key features of Cell Gap Junctions…
Formed by connexons.
Communicating junctions.
Allow ions and small molecules to pass from cell to cell.
Particularly important in heart cells and embryonic cells.
What is Diffusion?
The movement of molecules, or ions, from an area of higher concentration to a lower concentration. This is the concentration gradient.
What are three factors that affect diffusion?
Concentration - more collisions occur when the concentration difference is high.
Molecule size - smaller molecules are faster at diffusing
Temperature - more kinetic energy increases speed
What are two types of diffusion?
Simple - substances diffuse directly through lipid bilayer they tend to be small or gaseous, steroids or fatty acids.
Facilitated - substances either bind to proteins and are ferried or they pass through water filled channel proteins. These are selective in relation to pore size or charge of amino acids lining the channel.
What binds cells?
The glycocalyx.
Their contours fit together.
Special cell junctions.
What are microvilli?
Fingerlike projections that increase surface area for absorption.
Common in epithileal cells lining hollow body organs.
Membrane transport can take two forms, these are…?
Active - uses ATP (metabolic energy)
Passive - no energy required.
What is selective permeability?
The plasma membrane dictates which substances enter and exit the cell.
What is the process by which passive transport occurs?
Diffusion
What substances can pass directly through the plasma membrane?
Substances (molecules) that are fat-soluble.
What is osmosis?
The diffusion of water through a selectively permeable membrane.
Water may sneak through the lipid bilayer because of it’s small size.
Water moves freely through Aquaporins (trans-membrane) proteins.
Tonicity
refers to the ability of a solution to change the shape of a cell by altering it’s internal water volume.
Isotonic
Same concentrations of solutions inside as outside the cell.
Hypertonic
These have a higher concentration of non-penetrating solutes outside the cell. These call the cell to lose water.
Hypotonic
Have a lower concentration of non penetrating solutes and will continue to enter a cell until it burst.
How does the sodium - potassium pump work?
1 Three cytoplasmic Na+ bind to pump protein
2 Na+ binding promotes hydrolysis of ATP and the energy phsphorylates the pump.
3 Phosphorylation causes the pump to change shape and release Na+
4 Two K+ bind
5 K+ binding triggers release of phosphate and the pump then resumes it’s orignal position
6 Pump binds ATP and releases K+ and the Na+ sites are avaialbe for the cycle to repeat.
Secondary transport
Depends on the concentration gradient of primary transport. Just like a dam holding water to generate electricity, the gradient causes Na+ (for example) to try and rush back in and this pulls glucose against it’s concentration gradient.
Also sugars, amino acids, and ions are cotransported this way.
Vessicles
Bubble like membranes - transport stuff in exocytosis and endocytosis.
What are the three types of endocytosis?
Phagocytosis - cell eating - engulfs some large or solid material.
Pinocytosis - cell engulfs extracellular fluid. Important for intestinal cells.
Receptor-mediated endocytosis - highly selective for material only present in small amounts in the extracellular fluid.
What is exocytosis?
A substance is enclosed in a membranous vissicle which joines the plasma membrane and ejects the material outside of the cell.
What is the role of mitochondira?
They provide ATP for cell energy.
They carry out reactions where oxygen is used to breakdown food.
What are ribosomes?
Sites of protein synthesis.
Part of rough ER and free in cytoplasm
What does the Rough ER produce?
All proteins secreted from cells.
It’s also the membrane factory where integral proteins and phospholipids are manufactured.
What is the Golgi Apparatus?
Modifies, transforms, and packages proteins and lipids that are destined for export from the cell. These are substances that would have been produced by the rough ER.
What are lysosomes?
“disintegrator bodies” they dispose of invading bacteria, viruses, and toxins.
the eat up organlles that are old or dysfunctional
they breakdown glycogen stores for release
they break down bone to release calcium ions
they are the cell demolition crew.
What are peroxisomes?
these neutralize free radicals.
they detox alcohol and formaldehyde.
What are the three parts of the cytoskeleton (cell skeleton)?
Microfilaments - actin
intermediate filaments - tetramer fibrils
microtubules
Centrosomes and centrioles
cell center
organize mitotic spindle in cell division and form basis of cilia and flagella
cilia
moves material across cell
flagella
propels cell - sperm is the only one in the human body.
What are the subphases of interphase?
G1 - metabolically active, making proteins and doing it’s thing
S - DNA is replicated (synthesised)
G2 - stuff is replicated and the cell is prepped for division DNA is repaired where needed.
DNA Replication Sequence…
1 Uncoiling - enzymes unwind the DNA form a replication bubble.
2 Separation - DNA strands are separated
3 Assembly - DNA polymerase positions complementary free nucleotides along the template strands, forming two new strands. One leading end and one lagging end, due to the opposite directions.
4 Restoration - enzymes splice short segments of DNA together.
What is the role of RNA?
RNA is a decoder and messenger of DNA.
What are the three types of RNA?
tRNA - Transfer they decode mRNA for amino acids sequence
mRNA - Messenger carries coded info to the cytoplasm where protein synthesis occurs
rRNA - Ribosomal along with proteins form ribosomes
What are transcription and translation?
Transcription - DNA information is encoded in mRNA
Translation - mRNA is decoded and used to assemble poypeptides.
What are the 3 stages of Transcription?
1 Initiation - RNA polymerase binds to DNA and initiate mRNA synthesis.
2 Elongation - RNA polymerase “constructs” elongates mRNA one nucleotide at a time as directed by DNA.
3 Termination mRNA synthesis ends when the polymerase reaches a stop signal.
Oncogene
Has the potential to cause cancer.
When a cell begins to malfunction or processes are altered it should undergo apoptosis (rapid death). An oncogene can reprogram it to proliferate instead of die.
Tumor suppressor genes
Also, anti-oncogene. These are responsible for causing a damping effect on cell cycle or apoptosis. Sometimes both.
