Mcat Bio chapter 1

Cell theory

The theory stating that the cell is the basic functional unit of life, all living things are made of cells, cells are made from other cells, and cells contain DNA which is passed from parent to daughter cells

Basic functional unit of life

The cell

Eukaryotic cells - defining features

Contain membrane-bound organelles and a cytoskeleton

Nucleus

Membrane-bound organelle containing the cell's genetic material; includes the nuclear envelope, nuclear pores, and nucleolus

Nuclear envelope

Double membrane surrounding the nucleus

Nuclear pores

Openings in the nuclear envelope that regulate transport of molecules between the nucleus and cytoplasm

Nucleolus

Structure within the nucleus that serves as the site of ribonucleoprotein particle (ribosome subunit) assembly

Mitochondria

Membrane-bound organelle responsible for producing ATP; has outer and inner membranes, intermembrane space, matrix, and cristae

Mitochondrial cristae

Folds of the inner mitochondrial membrane that increase surface area for the electron transport chain

Mitochondrial matrix

Innermost compartment of mitochondria; site of the citric acid (Krebs) cycle

Intermembrane space (mitochondria)

Space between the outer and inner mitochondrial membranes

Mitochondria and apoptosis

Release of enzymes from the electron transport chain can trigger apoptosis (programmed cell death)

Mitochondrial DNA and ribosomes

Mitochondria contain their own DNA and ribosomes, supporting the endosymbiotic theory of their evolutionary origin

F0 portion (ATP synthase)

Membrane-embedded portion of ATP synthase that forms a proton channel

F1 portion (ATP synthase)

Portion of ATP synthase that catalyzes synthesis of ATP from ADP and phosphate as protons flow through F0

Lysosomes

Membrane-bound organelles containing hydrolytic enzymes used to break down waste materials and cellular debris

Autolysis

Self-digestion of a cell caused by release of lysosomal enzymes

Smooth endoplasmic reticulum (SER)

ER without ribosomes; involved in lipid and steroid synthesis and detoxification of substances

Rough endoplasmic reticulum (RER)

ER studded with ribosomes; involved in protein synthesis and export

Golgi apparatus

Organelle responsible for modifying, sorting, and packaging proteins for secretion or use within the cell

Peroxisomes

Membrane-bound organelles containing hydrogen peroxide that break down fatty acids via beta-oxidation; abundant in liver cells

Cytoskeleton components

Microfilaments (actin), intermediate filaments, and microtubules (tubulin)

Microfilaments

Cytoskeletal filaments made of actin; involved in muscle contraction (with myosin) and formation of the cleavage furrow during cell division

Intermediate filaments

Cytoskeletal filaments important for cell-cell adhesion, anchoring organelles, and withstanding tension; examples include keratin and desmin

Microtubules

Cytoskeletal filaments made of tubulin; work with kinesin and dynein motor proteins to transport vesicles, pull chromosomes apart during division, and form cilia and flagella

Kinesin and dynein

Motor proteins that move along microtubules to transport vesicles within the cell

9+2 structure

Arrangement of microtubules found in cilia and flagella (9 doublet microtubules surrounding 2 central microtubules)

Epithelial tissue

Tissue that covers the body and lines organs; constitutes the parenchyma (functional part of an organ); functions include defense against pathogens, absorption, and sensation

Parenchyma

The functional part of an organ, made up of epithelial tissue

Basement membrane

Layer underlying epithelial tissue that anchors it to underlying connective tissue

Polarized cells (epithelium)

Cells with distinct apical and basolateral membrane domains with different functions

Tight junction

Cell junction that seals adjacent epithelial cells together, preventing molecules from passing between cells

Adhesive belt (adherens junction)

Cell junction that connects actin filaments of adjacent cells, providing structural support just below the tight junction

Desmosome

Cell junction that anchors adjacent cells together via intermediate filaments, providing mechanical strength

Gap junction

Cell junction that allows direct communication between adjacent cells via channels connecting their cytoplasm

Connective tissue

Tissue that supports the body and provides a framework for epithelial cells; constitutes the stroma

Stroma

The support system of an organ, made up of connective tissue

Examples of connective tissue

Bone, cartilage, tendons, ligaments, adipose tissue, and blood

Three domains of life

Bacteria, Archaea, and Eukarya

Which domains contain prokaryotes?

Archaea and Bacteria

Archaea

Prokaryotic domain with genes/metabolic pathways more similar to eukaryotes than bacteria; live in extreme habitats (methanogens, thermophiles, halophiles) as well as the human body and soil; use alternative energy sources (light or chemicals)

Methanogens

Archaea that break down cellulose and produce methane

Thermophiles

Archaea (or other organisms) that thrive in high-heat environments

Halophiles

Archaea (or other organisms) that thrive in high-salt environments

Bacteria (general characteristics)

Prokaryotes found virtually everywhere (soil, water, digestive tract, hot springs, animals); can be symbiotic or pathogenic

Cocci

Spherical-shaped bacteria (e.g., Streptococcus)

Bacilli

Rod-shaped bacteria (e.g., Mycobacterium tuberculosis)

Spirilli

Spiral-shaped bacteria (e.g., Treponema pallidum, cause of syphilis)

Obligate aerobe

Organism that requires oxygen to survive

Obligate anaerobe

Organism that cannot survive in the presence of oxygen

Facultative anaerobe

Organism that can switch between using and not using oxygen

Aerotolerant anaerobe

Organism that does not use oxygen but is not harmed by its presence

Gram-positive bacteria

Bacteria with a thick cell wall containing lots of peptidoglycan and lipoteichoic acid; stain purple with Gram stain

Gram-negative bacteria

Bacteria with a thin cell wall containing little peptidoglycan and an outer membrane with phospholipids and lipopolysaccharides; stain pink-red with Gram stain

Lipopolysaccharide (LPS)

Component of the gram-negative bacterial outer membrane that triggers the host immune response

Prokaryotic cell structure

No nucleus or membrane-bound organelles; single-celled; DNA is one circular chromosome, may also have plasmids; has a cell wall (cell wall + membrane = envelope); may have flagella or fimbriae

Bacterial chromosome

Single circular DNA molecule containing the bacterium's genetic information

Plasmid

Small circular piece of extrachromosomal DNA in bacteria that can carry genes such as antibiotic resistance or virulence factors

Episome

A plasmid capable of integrating into the bacterial chromosome

Fimbriae

Hair-like appendages on bacteria used for attachment, similar in appearance to cilia

Bacterial flagella structure

Composed of a filament (made of flagellin), a hook (connects motor to filament), and a basal body (motor)

Chemotaxis

A cell's ability to detect a stimulus and move toward or away from it

Binary fission

Simple form of asexual reproduction used by bacteria in which a parent cell divides into two identical daughter cells

Bacterial genetic recombination

Transfer of genetic information from one organism to another; increases bacterial diversity and evolution over time; occurs via transformation, transduction, conjugation, and transposons

Transformation (bacteria)

Process by which a bacterium takes up plasmid DNA from its environment; the plasmid may integrate into the host chromosome via homologous recombination

Transduction (bacteria)

Process by which bacteriophages transfer short pieces of bacterial chromosomal DNA from one bacterium to another

Conjugation (bacteria)

Process by which a plasmid is transferred from one bacterium to another through a pilus

F+ cell

Donor bacterial cell in conjugation that has the fertility factor and codes for the pilus proteins

F- cell

Recipient bacterial cell in conjugation that lacks the fertility factor

Hfr cells

"High frequency of recombination" cells; bacteria in which the F plasmid has integrated into the bacterial chromosome

Transposons

Transposable elements; pieces of DNA capable of jumping from one location in the genome to another, which can move genes (like antibiotic resistance) between the chromosome and plasmids

Bacterial growth curve phases

Lag phase, exponential (log) phase, stationary phase, and death phase

Lag phase

Growth phase in which bacteria are adapting to new conditions before dividing

Exponential (log) phase

Growth phase characterized by a large increase in the number of bacteria

Stationary phase

Growth phase in which reduced resources slow bacterial reproduction, so growth rate levels off

Death phase

Growth phase in which bacteria have exceeded the resources of their environment and begin to die off

Virus structure

Nucleic acid (DNA or RNA) protected by a protein capsid; some viruses have a phospholipid envelope outside the capsid; viruses cannot reproduce independently

Capsid

Protein coat that protects a virus's nucleic acid

Viral envelope

Phospholipid membrane surrounding the capsid in some viruses, derived from the host cell membrane

Bacteriophage

A virus that specifically infects bacteria; injects its genetic material into the bacterium through its tail sheath

Viral genomes

Can be DNA or RNA, and single- or double-stranded; genome size varies from a few genes to hundreds of genes

Positive-sense RNA virus

Single-stranded RNA virus whose genome can be directly translated into protein by host ribosomes, acting like mRNA

Negative-sense RNA virus

Single-stranded RNA virus that requires synthesis of a complementary RNA strand (via RNA replicase carried by the virus) before translation can occur

Retrovirus

Single-stranded RNA virus that uses reverse transcriptase to convert its RNA into DNA once inside the host cell; the DNA then integrates into the host genome, making the virus very difficult to treat

Reverse transcriptase

Enzyme used by retroviruses to synthesize DNA from an RNA template

Steps of the viral life cycle

Infection, translation and progeny assembly, and progeny release

Viral infection (step)

Virus binds to a specific receptor on a host cell it can use (e.g., HIV binds the CCR5 receptor on white blood cells); depending on the virus, either the whole virus fuses in (e.g., HIV) or only genetic material is injected (e.g., bacteriophage)

Translation and progeny assembly (DNA viruses)

Viral DNA goes to the nucleus, is transcribed into mRNA, and is moved to the cytoplasm for translation

Translation and progeny assembly (RNA viruses)

Positive-sense: mRNA is translated directly in the cytoplasm; negative-sense: a complementary strand is made using RNA replicase before translation; retroviruses: RNA is reverse transcribed to DNA, which integrates into the host genome

Virion

A newly assembled, complete viral particle made up of capsid proteins and replicated viral genome

Progeny release

Release of new viral particles from a host cell, which can occur through cell death/lysis or through budding/extrusion from the plasma membrane

Productive cycle (viral)

Release of viral progeny via budding/extrusion, in which the host cell survives and continues to be used by the virus

Lytic cycle

Bacteriophage life cycle in which the phage replicates and lyses the host cell to release new phage particles; bacteria in this stage are termed virulent

Lysogenic cycle

Bacteriophage life cycle in which phage DNA integrates into the host genome (as a prophage/provirus) and is passed to daughter cells until stress triggers entry into the lytic cycle

Provirus / prophage

Viral DNA that has integrated into the host genome

Superinfection

Simultaneous infection of a cell by two different phage strains; infection with one phage strain makes the bacterium less susceptible to this

Prions

Infectious misfolded proteins that trigger the misfolding of other proteins, causing protein aggregates; cause diseases such as bovine spongiform encephalopathy (mad cow disease), Creutzfeldt-Jakob disease, and Alzheimer's disease

Viroids

Subviral plant pathogens consisting of very short circular single-stranded RNA that can bind to and silence plant genes

Hepatitis D

Example of a human viroid; if co-infected with Hepatitis B, it can silence genes in hepatocytes (liver cells)

Subviral particles

Infectious agents smaller and simpler than viruses, including prions and viroids