Cell Bio Exam 1 Review

Miller–Urey Experiment

Tested whether biologically relevant organic molecules could form abiotically when simple chemicals were exposed to energy under simulated early-Earth conditions

Miller–Urey Experiment Purpose

Investigated whether simple inorganic molecules could produce more complex organic molecules under conditions proposed for early Earth

Miller–Urey Experiment Basic Sequence

Simple molecules + environmental conditions + energy → chemical reactions → organic molecules

Did the Miller–Urey experiment create life?

No. It demonstrated that organic molecules associated with biological chemistry could form through nonbiological chemical processes

Why is the Miller–Urey experiment important to cell biology?

Cells require organic molecules and the experiment showed that biological building blocks could potentially arise through chemical processes before cells existed

First Principle of Cell Theory

All living organisms are composed of one or more cells

Second Principle of Cell Theory

The cell is the basic structural and functional unit of life

Third Principle of Cell Theory

Cells arise from preexisting cells

Importance of Cell Theory

It establishes the cell as the fundamental organizational unit of living systems

Prokaryotic Cell Organization

Has relatively simple internal organization and lacks a membrane-bound nucleus

Eukaryotic Cell Organization

Contains specialized internal compartments and membrane-bound organelles

Major Eukaryotic Organelles

Nucleus + ER + Golgi apparatus + mitochondria + lysosomes + peroxisomes + ribosomes + cytoskeletal structures

Importance of Eukaryotic Compartmentalization

Allows different biochemical processes to occur in specialized cellular locations

Location of DNA Transcription

Nucleus

Location of Protein Translation

Ribosomes

Location of Many Protein-Processing Events

Rough ER and Golgi apparatus

Location of Major Aerobic ATP Production

Mitochondria

Number of Major Differentiated Human Cell Types

More than 210

Differential Gene Expression

Different cell types activate different sets of genes and therefore produce different proteins and phenotypes

How can cells with essentially the same genome become different cell types?

They express different genes and therefore produce different proteins and cellular structures

Differentiation Sequence

Same genome → different genes expressed → different mRNAs → different proteins → different structures → different functions → different phenotype

Differentiation Key Principle

Differentiated cells generally contain the same genome but use different portions of their genetic information

Cellular Environment

Cells are extremely crowded microscopic environments containing macromolecules + ions + metabolites + membranes + organelles + cytoskeletal structures

Why does cell size matter?

Cell size affects diffusion + transport + metabolism + surface relationships + communication between cellular regions

Why is diffusion useful inside cells?

Microscopic intracellular distances allow molecules to encounter targets relatively quickly

Diffusion

Net movement resulting from random molecular motion that generally produces movement from higher toward lower concentration

Diffusion in the Cytosol

Allows substances to move through short intracellular distances and encounter enzymes or molecular targets

Cellular Scale and Diffusion

Short intracellular distances make diffusion effective for many molecular interactions

Magnification

Describes how much larger an image appears compared with the actual specimen

Resolution

Ability to distinguish two nearby structures as separate objects

Magnification vs Resolution

Magnification enlarges an image while resolution determines whether fine structures can actually be distinguished

Why is resolution more important than magnification?

Increasing magnification without sufficient resolution only produces a larger blurry image

Numerical Aperture or NA

Describes an objective's ability to collect light and resolve fine specimen detail

High Numerical Aperture

Higher NA → more useful light collected → better resolving ability

Low Numerical Aperture

Lower NA → less light collected → lower resolving ability

Upright Microscope

Objective is positioned above the specimen

Inverted Microscope

Objective is positioned below the specimen

Why can an inverted microscope be useful?

It allows the objective to observe cells growing in culture vessels from underneath

Fluorescence Microscopy

Uses fluorescent labeling to selectively visualize particular cellular structures or molecules

Fluorescence Principle

A fluorophore is excited by appropriate light and subsequently emits detectable light

Major Advantage of Fluorescence Microscopy

Molecular specificity allows selected targets to be distinguished from thousands of other cellular molecules

Confocal Microscopy

Uses fluorescence and laser illumination to isolate information from selected focal planes

Optical Section

Fluorescent image obtained from a selected focal plane within a specimen

Confocal Microscopy Advantage

Rejects much out-of-focus information and improves separation of structures located at different specimen depths

Fluorescence vs Confocal Microscopy

Standard fluorescence can collect signals from multiple depths while confocal microscopy provides optical sectioning

SEM

Scanning electron microscopy primarily examines surface morphology

TEM

Transmission electron microscopy uses electrons passing through a thin specimen to examine internal ultrastructure

SEM vs TEM

SEM emphasizes surface morphology while TEM emphasizes internal ultrastructure

AFM

Atomic force microscopy scans a surface with a very small probe to detect surface topography

Immunocytochemistry

Uses antibodies and specific antibody-antigen recognition to identify cellular molecules

Direct Immunocytochemistry

A detectable label is attached directly to the primary antibody recognizing the target

Indirect Immunocytochemistry

An unlabeled primary antibody binds the target and a labeled secondary antibody recognizes the primary antibody

Direct vs Indirect Immunocytochemistry

Direct detection labels the primary antibody while indirect detection uses a labeled secondary antibody

Advantage of Indirect Immunocytochemistry

Multiple secondary antibodies can contribute to a stronger detectable signal

Molecular Beacon

A horseshoe-shaped nucleic-acid probe containing a fluorophore and quencher that detects a complementary DNA or RNA sequence

Molecular Beacon Components

Nucleic-acid probe + fluorophore + quencher

Closed Molecular Beacon

Fluorophore remains close to the quencher and little fluorescence is detected

Target-Bound Molecular Beacon

Target binding opens the hairpin and separates the fluorophore from the quencher so fluorescence becomes detectable

Molecular Beacon Sequence

Target binds probe → hairpin opens → fluorophore separates from quencher → fluorescence becomes detectable

Plasma Membrane

Dynamic selectively permeable boundary separating the cell from its environment

Plasma Membrane Functions

Isolation + protection + environmental sensitivity + structural support + regulation of material entering and leaving

Phospholipid Bilayer

Basic membrane structure formed by phospholipids with hydrophilic regions facing water and hydrophobic regions facing inward

Hydrophilic Phospholipid Region

Interacts favorably with the aqueous environment

Hydrophobic Phospholipid Region

Avoids water and faces inward within the membrane

Phospholipid Bilayer Organization

Extracellular water → hydrophilic heads → hydrophobic tails → hydrophobic tails → hydrophilic heads → cytosol

Why does the phospholipid bilayer form a barrier?

Its hydrophobic interior restricts ions and many water-soluble compounds

Integral Membrane Protein

Protein embedded within the plasma membrane

Transmembrane Protein

Integral protein extending completely across the lipid bilayer

Peripheral Membrane Protein

Protein associated with one membrane surface rather than extending through the entire bilayer

Why are transmembrane proteins useful?

They interact with extracellular and intracellular environments and can function as channels + carriers + receptors

Anchoring Proteins

Connect the membrane to intracellular or extracellular structures and contribute to stability

Recognition Proteins

Function as cellular identifiers

Membrane Enzymes

Catalyze chemical reactions associated with the membrane

Receptor Proteins

Recognize extracellular ligands such as hormones and initiate cellular responses

Carrier Proteins

Bind specific molecules and facilitate their movement across the membrane

Channel Proteins

Provide selective pathways through which particular substances cross the membrane

Membrane Protein Principle

The lipid bilayer creates the basic barrier while membrane proteins provide many selective and communicative properties

Membrane Carbohydrate Structures

Glycoproteins + glycolipids + proteoglycans

Glycocalyx

Extracellular carbohydrate-rich sugar coat formed by membrane-associated carbohydrates

Glycocalyx Functions

Protection + lubrication + anchoring + locomotion + receptor specificity + immune recognition

Cilia

Cellular projections containing organized microtubules that move material across the cell surface

Cilium Microtubule Arrangement

9 + 2 arrangement of peripheral microtubule doublets surrounding a central pair

Centriole Microtubule Arrangement

9 + 0 organization involving microtubule triplets

Centriole Functions

Organization of cytoskeletal microtubules and chromosome movement during cell division

Cilia vs Centrioles

Cilia have a 9 + 2 doublet arrangement while centrioles have a 9 + 0 triplet organization

Ribosome

RNA-protein complex responsible for protein synthesis

Free Ribosomes

Ribosomes located within the cytosol

Bound Ribosomes

Ribosomes associated with rough endoplasmic reticulum

Basic Protein Synthesis Sequence

DNA → transcription → mRNA → translation at ribosome → polypeptide or protein

Endoplasmic Reticulum

Extensive network of membranous channels involved in synthesis + intracellular storage + intracellular transport

Rough ER

ER associated with ribosomes and involved in processing and packaging newly synthesized proteins

Smooth ER

ER lacking the ribosome-covered appearance and associated with lipid and carbohydrate-related synthesis

Rough ER vs Smooth ER

Rough ER primarily handles proteins while smooth ER is associated with lipids and carbohydrates

Golgi Apparatus

Stacks of cisternae involved in alteration + sorting + storage + packaging of cellular products

Cisternae

Flattened membrane compartments forming the Golgi apparatus

ER and Golgi Relationship

ER performs production and initial processing while Golgi performs further modification + sorting + packaging

Protein Trafficking Sequence

DNA → RNA → ribosome and rough ER → Golgi → vesicle → cellular destination

Protein Trafficking Step 1 Transcription

DNA information is transcribed into RNA inside the nucleus

Protein Trafficking Step 2 RNA Export

RNA carrying coding information moves from the nucleus toward cytoplasmic translational machinery

Protein Trafficking Step 3 Translation

Ribosomes read mRNA and assemble an amino-acid sequence