Unit 2: Cell Structure, Communication (Concepts and Terms)

Communications, Cell Structure, ETC.

chromatin

diffused DNA within the nucleoplasm of the eukaryotic cell

cillium

structure of microtubule pairs/9+1 structure

cilia vs. flagella

Cilia: rowing-like pattern; Flagella: undulating motion (think of snake's tail)

cytosol

cytoplasm of a eukaryotic cell; described as a colloidal dispersion

endoplasmic reticulum

communication network of membranes

golgi body

site for glycoprotein packaging before export

lysosomes

associated with intracellular digestion/hydrolytic enzymes of lipids, carbohydrates, and proteins

microfilament

associated with cyclosis and actin

microtubules

forms cellular internal "skeleton"

mitochondrion

site for glucose oxidation to ATP

mitochondria and chloroplasts

include compartments where hydrogen ions are concentrated

nucleolus

associated with RNA and ribosome subunits

peroxisomes

in plant cells, toxic hydrogen peroxide is broken down

plasma membrane

lipoprotein fluid mosaic structure; site for transport of materials in and out of the cell; molecules of cholesterol, phospholipids, and glycolipids in eukaryotes

plasmodesmata

cytoplasmic strands that extend through channels across a plant cell wall and connect adjacent cells

leucoplastid

plastid associated with storage

chromoplast/chloroplast

plastids; site for photosynthesis (glucose synthesis)

ribosomes

site for enzyme synthesis

vacuole

intracellular storage of wastes/food; in both animal/plant cells, resemble vesicles, but are involved w/storage

vesicles

in animal & plant cells; involved in transport of materials in/out of the cell

primitive earth's atmosphere (primordial) gases

methane (CH4), ammonia (NH3), hydrogen (H2), water vapor (H2O0)

evolutionary sequence from first anaerobic cell types to aerobic forms

first cell-like organisms (anaerobic heterotrophs) use fermentation to derive energy from food molecules, which increase CO2 levels --> photosynthetic (anaerobic autotrophs) arise, which increase Oxygen levels --> aerobic hetero-/autotrophs

evolutionary sequence of chemical energy processes

fermentation (CO2), photosynthesis (O2), respiration

only prokaryotic cells

- nucleoid
- cell wall with peptidoglycan and other non-cellulose polysaccharides
- rodlike pili for attachment to food/another cell
- flagella formed by protein flagellin
- single continuous molecule of DNA

compare/contrast prokaryotic and eukaryotic cells

- cell membrane present in both
- ribosomes present (smaller in bacteria)
- prokaryotes structurally less complex than eukaryotes
- no organelles

animal & plant eukaryotic cells both have

- multiple DNA w/histone proteins
- mitochondria
- nuclear envelope

only animal eukaryotic cells

- lysosomes
- centrioles
- cilia/flagella formed from microtubules

only plant eukaryotic cells

- cell walls have pectin, lignin, cellulose
- chromoplasts & leucoplasts (plastids)
- chloroplasts with chlorophyll
- no lysosomes!

Be able to calculate and compare surface area to volume ratios for different cell-simulated shapes.

Cells need to have a high surface area to volume ratio. This helps materials be transported in and out, and this is also why cells are so small.

- Surface area-to-volume ratios affect the ability of a biological system to obtain necessary resources, eliminate waste products, acquire or dissipate thermal energy, and otherwise exchange chemicals and energy with the environment

- Smaller SA → the bigger you are!

The surface area of the plasma membrane must be large enough to adequately exchange materials.

a. These limitations can restrict cell size and shape. Smaller cells typically have a higher surface area-to-volume ratio and more efficient exchange of materials with the environment.

b. As cells increase in volume, the relative surface area decreases and the demand for internal resources increases.

c. More complex cellular structure (like membrane folds) are necessary to adequately exchange materials with the environment.

d. As organisms increase in size, their surface area-to-volume ratio decreases, affecting properties like rate of heat exchange with the environment.

Be familiar with the endosymbiotic theory evidence for the origin of chloroplasts and mitochondria.

The endosymbiotic theory proposes that eukaryotic cells formed from a symbiotic relationship among prokaryotic cells.

- Organelles like mitochondria and chloroplast were once free-living prokaryotes that began to live within a larger host cell

- Over a longer time, these prokaryotes and hosts evolved until one could not function without the other

There are several hypotheses about the origin of life on Earth that are supported with scientific evidence.

Earth formed 4.6 billion years ago, but the environment was too hostile for life until 3.9 bya. The earliest fossil evidence for life dates to 3.5 bya.
- This evidence provides ranges of dates when the origin of life could have occurred.

What are some observations that support the endosymbiotic theory?

- Double membranes → mitochondria have their own cell membranes, just like prokaryotes

- Ability to reproduce/ replicate → mitochondria multiply by pinching in half, which is the same as bacteria

- DNA in mitochondria and choloplasts → each mitochondrion has its own circular DNA genome

- This is like a bacteria’s genome, only smaller

- Synthesize proteins

So how would we answer a question that is along the lines of: “How do we know that the organelle evolved from prokaryotic organisms?”

- Look for double membranes → indication that the organelle contains its own DNA

- Look for ribosomes → one observation is that proteins are synthesized, and they could not be synthesized without ribosomes

Protein Synthesis

process by which cells create proteins using genetic instructions from DNA

similarities/differences between prokaryotic and eukaryotic cells in terms of completing processes like respiration and photosynthesis:

- same chemical processes, equations, ETC
- prokaryotes perform it in specialized membrane folds
- eukaryotes perform it in membrane-bound organelles

Prokaryotes vs. Eukaryotes: Genetic Information

Prokaryotes: DNA is circular, usually free-floating in cytoplasm
Eukaryotes: DNA is linear, found in nucleus

Prokaryotes vs. Eukaryotes: Organelles

Prokaryotes: No nucleus or membrane-bound organelles
Eukaryotes: Has nucleus and membrane-bound organelles (ie: mitochondria, chloroplasts, Golgi body, ER)

Prokaryotes vs. Eukaryotes: Size

Prokaryotes: Small (1-5 micrometers)
Eukaryotes: Larger (10-100 micrometers)

Prokaryotes vs. Eukaryotes: Organisms

Prokaryotes: Bacteria/archaea
Eukaryotes: Animals, plants, fungi, protists

Prokaryotes vs. Eukaryotes: Cell Structure

Prokaryotes: Always unicellular
Eukaryotes: Can be unicellular or multicellular

Be familiar with cell specialization and what makes a cell specialized as compared to a non-specialized cell – relate to genes active and not active

- All cells have identical genetic material, but different gene expressions lead to specialization in cell types.
- Developmentally, specific genes are activated or silenced

what makes a cell specialized?

- specific functions
- elaboration or loss of organelles (some genes turned on/off), inter-dependent on other cells

cell organelles interacting for defense/secretion

- DNA in nucleus has instructions transcribed into mRNA
- ribosomes on rough ER make the protein
- proteins travel through the ER (channel)
- transport via vesicles to golgi apparatus to get packaged & addressed
- transported out of golgi via vesicle to membrane for secretion

cell organelles interacting for defense

lysosomes made by rough ER ribosomes and will latch onto invading bacteria/viruses and kill it

ribosomes associated with the cytoplasm make proteins

used by organelles and throughout the cell

ribosomes associated with the rough ER make proteins

to be secreted, be on the membrane, or in lysosomes

Be familiar with steps of the signal transduction pathway

1. Signal. The ligand binds to the receptor. The ligand can be a hormone, neurotransmitter, or another signaling molecule

2. Transduction. There are several important vocabulary terms here to know here.

- Types of receptors: GPCRs (G protein-coupled receptors), receptor tyrosine kinases, and intracellular receptors. Know the transduction mechanism for each

- Second messengers. The most common examples to know are cAMP and Ca2+ (calcium ions). Know how the DAG pathway with Ca2+ and IP3 works

- Phosphorylation cascade = a chain of phosphorylation (adding a phosphate group to a molecule, a protein in this case), which often occurs as part of transduction. The purpose of the phosphorylation cascade is to amplify the original signal

3. Response. This can be turning off expression of a particular gene, increased uptake of an ion, increasing production of a specific enzyme, or many other changes

Kinase

enzyme that adds a phosphate group to another molecule, usually to activate it

Phosphatase

enzyme that removes a phosphate group from another molecule

How do kinase and phosphatase work together?

Kinases and phosphatases work together to activate and deactivate molecules in the signal transduction pathway

Be familiar with basics of immune responses

The immune system defends against pathogens, infectious agents such as bacteria, viruses, protists, and fungi that cause disease.

Non-specific Immunity (innate)

external physical barriers and internal defenses of immune cells (neutrophils, natural killer cells) that have a small group of receptor proteins that recognize a broad range of pathogens (toll-like receptors)

Specific (acquired) Immunity

line of defense in vertebrates in which immune cells react specifically to pathogens. A vast array of acquired immune receptors allow recognition and response to specific pathogens. (includes B cells; T cells; Plasma cells; antibodies)

Humoral (B cell receptors and antibodies)

recognize intact antigens that are either molecules on the surfaces of infectious agents or molecules free in the body

T cell receptors

recognize pieces of antigens that have complexed with an MHC molecule inside a cell and are then presented on the cell surface

Cytotoxic T Cells

recognize foreign antigens that have been manufactured by a body cell and displayed with class I MHC molecules (involve CD8 docking proteins)

Helper T Cells

recognize antigen fragments from microbes that have been engulfed by antigen presenting cells (dendritic cells, macrophages, and B cells) and displayed with Class II MHC molecules (involve CD4 docking proteins)

Heterotroph Hypothesis

Proposed by Oparin; inorganic precursors synthesized organic molecules on primitive Earth

Miller-Urey/ Stanley Miller Experiment

- demonstrate the formation of organic compounds (e.g., amino acids) from inorganic sources under early Earth conditions
- primitive earth's atmosphere gases: methane, ammonia, water vapor, carbon dioxide, hydrogen, and nitrogen (Miller-Urey and Stanley Miller experiment)

Review information presented in the heterotroph hypothesis on the origin of life.

1. Formation of anaerobic heterotrophs that relied on organic molecules.

2. Development of autotrophs capable of photosynthesis, which introduced oxygen into the atmosphere.

3. Evolution of aerobic respiration as a response to the oxygenated environment, enabling more efficient energy production.

RNA World Hypothesis

- Proposes RNA as the earliest form of genetic material.
- RNA can self-replicate and has diverse functions beyond protein synthesis.
- Ribozymes: RNA molecules that act as enzymes.
- RNA's ability to code, replicate, and mediate reactions supports its central role in early life.