chapter 3: a&p (cells)

What is a cell?
Cell theory:
- The cell is the smallest unit of life.
- All organisms are made of one or more cells.
- Cells only arise from other cells.

- Trillions of cells in the body divided over 250 cell types
- 2 micrometers to over 1 meter long nerve cells

- All share: plasma membrane, cytoplasm, nucleus

Extracellular Materials

- Extracellular Fluid (ECF): includes interstitial fluid, blood plasma, cerebrospinal fluid
- dissolves & transports fluids
- Cellular Secretions: such as gastric & intestinal fluids (digestion), saliva & mucus (lubricants)
- Extracellular Matrix (ECM): mesh assembled from proteins and polysaccharides that bind cells together
- particularly abundant in connective tissues

Lipids
- Phospholipid Bilayer:
- thin, fluid
- embedded proteins
- cholesterol β†’ add structure


Proteins
- transport substances in & out cells
- receptors: sense materials (1 side communicate to other πŸ”)
- enzymes: catalyze reactions
- ECM attachment anchor to cell membrane to surrounding matrix
- cell to cell contact
- no tissue sheets to hold together


Carbohydrates
- glycocalyx
- glycoprotein
- glycolipid

Cell Junctions

1. tight junction:
- tightly fused, impermeable, no passing of other materials, prevent movement
(ex: intestinal tract)
2. desmosomes:
- anchoring junctions, distribute tension, & prevent stretching
(ex: stretching muscle & skin)
3. gap junctions:
- communicating junctions (protein channels) thats allow material exchange
(ex: cardiac cells & other contract)


Membrane Transport:
- Selective Permeability: only substances meeting certain criteria can pass through unaided
- hydrophobic
Passive Transport: movement across a membrane without expended cellular energy (along concentration gradient) (high to low)
1. simple diffusion β†’ C2, O2
2. facilitated diffusion β†’ helper protein β†’ carrier (or) channel mediated β†’ leakages (or) gated
3. osmosis β†’ H2O against (aquaporin)

Tonicity:


Active Transport: movement across a membrane that requires ATP
1. primary & secondary
- sodium potassium pump (protein) pump splits ATP & moves substances
- co-transporter to use energy of concentration gradient (moving against crowd)
2. vesicular transport
- endocytosis & exocytosis
- phagocytosis (cannibalism)
-
pinocytosis (take in fluid)
-
receptor mediated endocytosis

Membrane Potential
- Voltage across membrane
- Voltage: electrical potential energy from separation of charge particles
- Established by diffusion, maintained by active transport


1. Leakage Channels = K+ Loss from Cell
2. Some K+ moves back into cell, attracted to - charge of inner membrane
3. Balanced K+ gradient occurs at -90 mV

Plasma Membranes:
- Cell Adhesion Molecules (CAMs): glycoproteins that maintain cell anchors, move migrating cells, send SOS signals after damage, transmit environmental information
- Membrane Receptors:
- Contact Signaling: cell-cell recognition, important in development & immunity
- Chemical Signaling: extracellular ligands bind to receptors to initiate a response (e.g., hormones, neurotransmitters); response is cell-type specific
- Initiate release of G proteins from receptors into cells, & activate different types of responses

Cytoplasm
- Cytoplasm: internal contents of a cell
- Cytosol: jelly-like filling; fluid medium for biochemical reactions
- Inclusion: additional chemical substances
- Organelle: membrane-enclosed bodies for a specific function

- Nucleus: central organelle holding DNA



Endomembrane System
- system of organelles that work together to produce, store, and export biological molecules

1. Nucleus
2. ER (Rough & Smooth)
- Rough: protein synthesis for outside cell
- Smooth: lipid synthesis (phospholipid, cholesterol)
- steroid hormones
- store calcium
3. Golgi Apparatus
- postal service of cell
- modify molecules
4. Exocytosis OR Lysosomes
- digestive enzymes & clean out (autophagy) autolysis: cell death/destruction
5. Peroxisomes
- detoxify & neutralize free radicals (ROS); highly reactive products of cellular processes that contain oxygen (OH, H2OO2, O2)
- Oxidative stress: damage caused by ROS
6. Mitochondria
- provide majority of ATP
- High density in cells with high energy needs
- Smooth outer membrane and folded inner membrane with cristae
- Metabolism occurs in internal matrix
7. Ribosomes
- protein synthesis
- Built of two subunits
- Free or membrane-bound

Cytoskeleton
1. Microtubules: thick filaments, tubulin
- Cilia & flagella
- resist compression

- centrioles
2. Microfilaments: thin filaments, actin
- contraction & cell division
3. Intermediate Filaments: keratin
- cell adhesion
- resist tension


Cellular Extensions:
- Cilia: whiplike extensions to move substances across cell surfaces
- Flagella: substantially longer than cilia to propel a cell
- Only present in humans in sperm cells
- Microvilli: finger-like projections that increase cell surface for absorption (not movement)


Nucleus:
- stores genetic information
(ex: DNA)
- Multinucleated: multiple nuclei
- Anucleate: no nucleus

Nuclear Envelope: lipid bilayer with passages called nuclear pores
Nucleolus: manufactures ribosomes



Chromosomes


Cell Cycle
- Interphase
G1: prep for DNA replication
S: DNA replication
G2: prep for cell division
- Mitosis (Cell Divide)
1. Prophase
- condense chromosomes
- lose nucleus & activate centrioles
2. Metaphase
- chromosomes line up in the middle
3. Anaphase
- chromatids pull apart
- moved by centrioles
4. Telophase/Cytokinesis
- 2 nuclei form
- cytoplasm, membrane divide
- Cytokinesis


G0: rest phase between cell divisions or in cells that cannot divide


Control of Cell
- ratio of SA:V ⬆ Cell ⬇ Movement
- chemical signal
- space to grow
- interphase checkpoints ruled by cyclins (mitosis) & cyclin dependent kinases (cdks)
* Contact Inhibition:
- no space to put new cells so mature tissue & control growth

Central Dogma
(Nucleus) (Ribosomes)
DNA (genetic code) β†’ RNA (messenger) β†’ Protein
transcription translation


Transcription: DNA β†’ RNA
1. Initiation: proteins bind to designated gene promoter
2. Elongation: RNA polymerase unwinds DNA and writes mRNA along one strand
3. Termination: terminator sequence causes RNA to unbind DNA and RNA pol

RNA processing
- Exon: portion of transcript that codes for proteins
- Intron: non-coding parts in-between
- Splicing: removal of non-coding transcript sequence

Translation: RNA β†’ Protein
1. Initiation: ribosomes binds to mRNA
2. Elongation: tRNA matches amino acid to RNA sequence
3. Termination: tRNA reaches the stop codon and releases the peptide




DNA Replication:
1. Initiation: helicase & other enzymes unwind DNA
- Helicase
- Unzip DNA strand
- Promoter / Ribosome
2. Elongation: DNA polymerase builds the complementary strand along each template
- Primase
- keep DNA apart through primase
- DNA polymerase
- replace primer & new DNA
- RNA polymers' unwind DNA
- tRNAs
3. Termination: two new strands are complete & each fused to an original strand
- Ligase
- connect & ligase new DNA strand
- Terminator
- Stop Codon
- Semiconservative



Messenger RNA
- Gene: segment of DNA with instructions to build one polypeptide
- copied from DNA to mRNA, then from mRNA to protein
- made up of exons and introns
- Encoded in there base-long triplets

- mRNA
carry protein code
- rRNA
form ribosome
- tRNA
build proteins

Autophagy & Apoptosis
- Autophagy: removal of unnecessary, damaged, or stressed cell components
- Allows removal of unneeded proteins & structures
- Cannibalizes portions of cells during starvation & stress
- Restructures cells during development
- Ubiquitin-proteasome Pathway: marks & destroys misfolded or damaged proteins
- Apoptosis: programmed cell death to remove cells with limited life spans
- Mitochondria leak factors that trigger caspases to digest internal components