C1 - The Cell Flashcards
First person to view a living cell under a microscope
Anton Van Leeuwenhoek (1674)
In 1850, what did Rudolph Virchow very famously demonstrate?
That diseased cells could arise from normal cells in normal tissue
What are the 3 basic ORIGINAL basic tenets of cell theory?
All living things are comprised of cells
The cell is the basic functional unit of life
Cells arise from preexisting cells
Through advancements in molecular biology what was the fourth tenet that was added?
Cells carry genetic information in the form of Deoxyribonucleic acid (DNA), this genetic material is passed on from parent to daughter cell
What is the dilemma with viruses pertaining to the cell theory?
Viruses contain genetic material but are unable to reproduce on their own, this violates the 3rd and 4th tenet because they can ONLY duplicate by invading other organisms
Viruses are considered non-living
Main difference between eukaryotic and prokaryotic organisms
Prokaryotic are always single celled and do not contain a nucleus, eukaryotic are unicellular or multicellular, cell contains a nucleus enclosed in a membrane
Organelles are suspended in what?
Cytosol
What allows diffusion of molecules throughout the cell?
Cytosol
What is the nuclear envelope
A double membrane that maintains a nuclear environment separate and distinct from the cytoplasm
What are nuclear pores?
They are pores in the nuclear membrane allowing a selective 2 way exchange of materials between the cytoplasm and nucleus
DNA consists of coding regions called…
genes
Chromosomes are composed how structurally
Linear DNA that is wound around organizing proteins called histones, further wound into linear strands called chromosomes
What gets synthesized in nucleolus?
ribosmal RNA (rRNA)
Mitochondria outer and inner membrane functions
Outer membrane serves as a barrier between the Cytosol and inner environment of mitochondria
The inner membrane houses molecules and enzymes of the electron transport chain
How is the inner membrane of the mitochondria arranged?
Into numerous folding called cristae which are highly convoluted structures that increase the surface area available for electron transport chain enzymes
Inside space in the inner membrane of mitochondria is called what?
The mitochondrial matrix
Where does the pumping of protons go from the mitochondrial matrix?
To the inter-membrane space
What does mitochondria contain distinct from most other organelles?
Some of their own genes and replicate independently of the nucleus via binary fission
How are mitochondria capable of killing cells?
By releasing enzymes from the electron transport chain, this release kickstarts the process of apoptosis
What are lysosomes
A membrane bound structure containing hydrolytic enzymes capable of breaking down different substances
What are endosomes?
Endosomes help lysosomes, which can transport, package, and sort cell material traveling to and from the membrane
Endosomes are capable of transporting materials to what?
Trans-Golgi, cell membrane, or to lysosomal pathway for degeneration
When lysosomes release their hydrolytic enzymes it results in what?
Apoptosis
What is autolysis
The process of self digestion that occurs when lysosomal enzymes are released into the cytoplasm, leading to breakdown of cellular components and eventual cell death
Describe the the endoplasmic reticulum’s membrane?
A series of interconnected double membrane with many invaginations containing spaces inside called lumen. It is actually continuous with the nuclear envelope
What is the ROUGH endoplasmic reticulum?
The part of the endoplasmic reticulum studded with ribosomes which permit the translation of proteins destined for secretion directly into lumen
What is the smooth endoplasmic reticulum?
This area lacks ribosomes, utilized primarily for lipid synthesis and detoxification of certain drugs and poisons, also transports proteins from RER to the Golgi apparatus
What is the structure of the Golgi apparatus made of
It is made of stacked membrane bound sacs
Describe the process of materials getting to the Golgi apparatus and then where it goes after? (Including when it is in the Golgi apparatus)
materials go from endoplasmic reticulum to Golgi apparatus in vesicles, once there these cellular products may be modified, can also direct the delivery of the product to a specific location
If the product is destined for secretion in the Golgi apparatus what happens?
The secretory vesicle merged with the cell membrane and it’s contents are released via exocytosis
What do Peroxisomes contain?
Hydrogen peroxide
What does Peroxisomes break down?
Fatty acids via beta-oxidation
Cytoskeleton function
Provided structure to the cell and helps it to maintain its shape
Also provide a conduit for the transport of materials around the cell
3 components of cytoskeleton
Microfilaments
Intermediate filaments
Microtubules
Describe structure and function of microfilaments
Microfilaments are made up of solid polymerized rods of actin, these filaments are organized into bundles and are resistant to both compression and fracture providing protection for the cell
Cytokinesis
Process of cell division in which the cytoplasm of a parent cell divides into 2 daughter cells
What are microtubules?
Hollow polymers of tubilin proteins, they radiate throughout the cell, providing the primary pathways along which motor proteins like kinesin, and dynein carry vesicles
What are cilia and flagella and why are they similar?
They are motile structures sharing the same structure, composed of nine pairs of microtubules forming an outer ring with 2 microtubules in the center, known as the 9 + 2 structure
Main difference between cilia and flagella
Cilia are projections from the cell primarily involved in the movement of materials along the surface of cells, flagella help movement of cells itself
Where are centrioles found?
In the central region of the cell called the centrosome
What are centrioles?
The organizing centers of the microtubules structured as 9 triplets of microtubules with a hollow center
What do centrioles do during mitosis?
Migrate to opposite poles of the dividing cell and organize into the mitotic spindle
What do microtubules from the centrioles attach to?
Chromosomes via complexes called kinetochores which pull the sister chromatids apart
What are intermediate filaments and what do they do?
They are a diverse group of filamentous proteins, many intermediate proteins are involved in cell-cell adhesion, also help anchor organelles, including the nucleus
They are able to withstand a tremendous amount of tension
What are the 4 types of tissue?
Epithelial, nervous, connective, and muscle
What does epithelial tissue do?
Covers the body and lines it’s cavities, providing protection against pathogens invasion, in certain organs they are involved in absorption, secretion, sensation
What is underneath epithelial tissues
Connective tissue called Basement membrane
Epithelial cells are often polarized, meaning…
One side faces a lumen (hollow inside of an organ or tube) while the other side interacts with underlying blood vessels, and structural cells
What does connective tissues do?
Supports the body and provides a framework for the epithelial cells to carry out their functions
Most connective tissue produce and secrete what?
Materials such as collagen and elastin to form the ECM
Epithelial cells, and connective tissue are often known to contribute to what aspect of human anatomy respectively?
Epithelial cells contribute to the parenchyma (functional part of the organ) while connective tissue contributes to the stroma or support structure
How is genetic material arranged in prokaryotes? Where are they located?
Into a single circular molecule of DNA in an area of the cell called the nucleoid region
All bacteria are classified as
Prokaryotes
What are the 3 overarching domains of life?
Archea
Bacteria
Eukarya
What are archea?
Single celled organisms, contain genes and several metabolic pathways similar to eukaryotes, ability to use alternative sources of energy
Eukaryotes and archea are similar in the fact of translational division how?
They both start translation with Methionine, contain similar RNA polymerases, and associate their DNA with histones
How do archea divide?
By binary fission or budding
All bacteria contain what? Some have what?
A cell membrane, cytoplasm, and some have flagella or fimbriae
Why can it be difficult to develop medicines that only target bacteria? But also how can they still target specific bacteria?
Because they often share analogous structures to eukaryotes, in some cases even similar structures have enough biochemical differences to allow the exclusive targeting of one kind of organism
Does bacteria outnumber human cells in the body?
Yes by 10:1
Some bacteria are mutualistic symbiotes, what does this mean?
That both humans and the bacteria benefit from the relationship
Pathogenic bacteria can live where?
Both intracellular and extracellular
Most bacteria exists in one of what 3 shapes?
Spherical bacteria (cocci)
Rod-shaped bacteria (bacilli)
Spiral-shaped bacteria (spirilli) very few pathogenic bacteria are spiral
What are obligate aerobes?
Bacteria that requires oxygen for metabolism
Bacteria that used fermentation or some other cellular metabolism that does not require oxygen are called what?
Anaerobes
What are the types of anaerobes? Describe them
Obligate anaerobes - cannot survive in a oxygen-containing environment
Facultative anaerobes - can toggle between metabolic processes, using oxygen for aerobic metabolism if present, switching to anaerobic metabolism if not
Aerotolerant anaerobes - unable to use oxygen for metabolism but are not harmed by its presence in the environment
How are Prokaryotes envelope composed?
The cell wall forms the outer barrier of the cell, next layer is the cell membrane, together they are known as the envelope
What are the 2 types of cell walls in bacteria?
Gram positive and gram negative
How is the type of cell wall determined? Describe how
By the gram staining process: in which a crystal violet stain, followed by a safranin counter stain
If the envelope absorbed the crystal violet stain it will appear deep purple, cell is considered to be gram positive
If the envelope does not absorb crystal violet stain, but absorbs safranin counterstain, cell will appear pink-red and said to be gram negative
Describe the main takeaways of a gram positive cell wall
Consists of a thick layer of peptidoglycan, a polymeric substance made from amino acids and sugars
May also aid a bacterial pathogen by providing protection from a host organisms immune system
Contains lipoteichoic acid, human immune system may be activated by exposure to these chemicals
Describe the main takeaways of gram negative cell wall
Cell walls are very thin and also contain peptidoglycan but in much smaller amounts
Peptidoglycan cell walls are separated from the membrane by the periplasmic space
Outer membranes contain phospholipids and lipopolysaccharides
Lipopolysaccharides triggers immune response in human beings, inflammatory response to these are much stronger than the response to lipoteichoic acid
How are flagella used?
For propulsion, and to move towards food or away from toxins, immune cells
What is chemotaxis?
The ability of a cell to detect chemical stimuli and move towards or away
Flagella is composed of what parts? Describe each one
Filament - a hollow, helical structure composed of flagellin
Basal body - anchors the flagellum to the cytoplasmic membrane, also a motor of the flagellum, rotating up to 300HZ
The hook - connects the filament and the basal body so that as the body rotates, it exerts torque on the filament, spinning and propelling the bacterium forward
What are plasmids?
Plasmids carry DNA that is not necessary for survival of the prokaryote
not considered a part of the genome
In prokaryotes what is used for the electron transport chain and generation of ATP? And why?
The cell membrane since prokaryotes lack mitochondria
Size difference in prokaryotic and eukaryotic ribosomes
Prokaryotic ribosomes - contain 30S and 50S subunits
Eukaryotic ribosomes - contain 40S and 60S subunits
How do prokaryotes reproduce?
Via asexual reproduction in the form of binary fission
Describe the process of binary fission
In binary fission the circular chromosomes inside the cell wall replicate then an inward pinch (invagination) occurs in the midline separating them into 2 daughter cells
It requires fewer events than mitosis, so it proceeds more rapidly
Many bacteria contain extrachromosomal (extragenomic) material called what? And what does it do?
They are known as plasmids, they offer some benefits to the bacterium like antibiotic resistance, they also carry additional virulence factors, or traits that increase pathogenicity, such as…
-Toxin production
-projections allowing attachment of certain kinds of cells
-or features that allow evasion of hosts immune system
What are episomes?
A subset of plasmids that are capable of integrating into the genome of the bacterium
What is bacterial genetic recombination?
A process that helps increase diversity and this permits evolution of bacterial species over time
Processes include transformation, conjugation, and transduction
How does transformation of bacterial genetic recombination occur?
It results from the integration of foreign genetic material into the host genome
Most frequently coming from other bacteria upon lysing, spilling their contents into the vicinity of the bacterium
What is the conjugation process of bacterial genetic recombination? And describe the process briefly
It is the bacterial form of sexual reproduction, Involves 2 cells forming a conjugation bridge
The transfer is unidirectional from donor male (+) to recipient female (-)
How is the conjugation bridge made? What must it contain in order for it to bridge?
From appendages called sex pili found on donor male (+)
To form the pilus (conjugation bridge) bacteria must contain plasmids known as sex factors, bacteria possessing the plasmid are termed F+cells, those without are F-cells
How is the sex factor given around in conjugation? And what is the purpose?
During conjugation F+ cells replicate its F factor and donates it to the F- cell, converting it into an F+ cell enabling it to go on and transfer more copies to other cells
This allows for rapid acquisition of antibiotic resistance or virulence factors
Is the sex factor a plasmid?
Yes, but through transformation it can become integrated into the host genome
What is High frequency of recombination (HFR)?
refers to a state in bacterial cells where the F factor (fertility factor) is integrated into the host chromosome. This integration allows for more frequent exchange of genetic material during conjugation, leading to a higher rate of recombination between the bacterial genomes.
What is transduction of the bacterial genetic recombination process?
It is the only genetic recombination process that requires a vector (a virus that varies genetic material from 1 bacterium to another)
Viruses are usually what type of obligate?
Obligate intracellular pathogens, meaning they cannot reproduce outside of a host cell
Bacteriophages can accidentally incorporate a segment of host DNA during assembly, what results from it?
When it infects another bacterium, it can release this trapped DNA into the new host cell giving the cell new additional genes
What are transposons?
Genetic elements capable of inserting and removing themselves from the genome
What phase do bacteria first adapt to the new local conditions?
Lag phase
As bacteria adapts and division increases what does it cause?
An exponential increase in the number of bacteria in the colony during the exponential phase, also called log phase
As number of bacteria in colonies grow, resources are often reduced
Reduction of resources slows reproduction, what phase is the bacteria in?
Stationary phase
What is the final stage of bacterium
Death phase marking the depletion of resources
What are viruses composed of?
-Genetic material varying between DNA, RNA, circular, or linear
-a protein coat
-sometimes an envelope containing lipids
What is the virus protein coat called? What could be surrounding the coat?
It is known as a capsid which may be surrounded by an envelope composed of phospholipids and virus specific proteins
Difference between envelope and non enveloped viruses?
The Envelope is very sensitive to heat, detergents, and desiccation, thus enveloped viruses are easier to kills, viruses that do not have an envelope are more resilient to sterilization and are likely to persist on surfaces over a long period of time
Why must viruses express and replicate genetic information within a host cell?
Because they lack ribosomes to carry out protein synthesis
Instead of entering bacteria what do bacteriophages do?
Inject their genetic material, leaving the remaining structures outside the infected cell
Bacteriophages contain a tail sheath and tail fibers, what do they do?
Tail sheath - can act like a syringe, injecting genetic material into a bacterium
Tail fibers - help the bacteriophages recognize and connect to the correct host cell
Single-stranded RNA viruses can be what 2 types?
Positive sense - the genome may be directly translated to functional proteins by ribosomes of the host cell
Negative sense - acts as a template for synthesis of a complementary strand, which then can be used as a template for protein synthesis
What are retroviruses?
A virus that uses RNA as its genetic material that can can insert its genetic material into the DNA of the cells it infects. This allows the virus’s genetic information to become a permanent part of the host cell’s genetic code.
Usually retroviruses contain what type of enzyme? What does it do? What is caused because of it?
Reverse transcriptase, this enzyme synthesizes DNA from single-stranded RNA, the DNA is then integrated and replicated in the host cells DNA like it is its own, this allows the cell to be infected indefinitely
The only way to remove the infection is to kill the infected cell
Why is HIV (human immunodeficiency virus) so hard to treat?
Because it is a retrovirus
Why can viruses only infect a specific set of cells?
Because without the proper receptors a cell is essentially invisible to the virus
HIV must bind to what in order for the cell to get it?
A receptor called CCR5 on white blood cells in order to infect them
Interestingly some people lack this receptor and are thus immune to HIV
What happens when the host cell mistakes a virus bound to the membrane as nutrients?
It will simply bring the virus into the cytoplasm via endocytosis
Some tail fibers on bacteriophages even have enzymatic activity, what does this cause?
Both penetration of cell wall, and formation of pores on cell membrane
What is a virion?
A virion is a complete, individual virus particle that consists of genetic material (DNA or RNA) surrounded by a protective protein coat called a capsid. It is the infectious form of a virus and is capable of infecting host cells to replicate and produce more virions.
What is important to remember with how certain viruses insert virions into host cells?
The entry mechanism varies depending on the virus and the type of host cell it targets
Understanding these mechanisms is crucial for developing antiviral therapies and vaccines.
Most DNA viruses must enter where in order to be transcribed into mRNA?
The nucleus
Where does positive - sense RNA viruses go?
They stay in the cytoplasm, where it is directly translated into proteins by host cell ribosomes
What must happen before a negative - sense RNA viruse can be translated to form proteins?
It requires synthesis of a complementary RNA strand via RNA replicase
What is a capsid?
A protein coat surrounding a virus
Reverse transcriptase in retroviruses travel where?
To the nucleus where it can be integrated into the hosts genome
Once the viral genome has been replicated what happens?
It can get packaged within the capsid
The viral genome must be returned to its original form before packaging
Steps of how viral progeny release can happen?
First, the viral invasion may initiate cell death, results in spilling of viral progeny
Second, the host cell may lyse as a result of being filled with extremely large numbers of virions, this causes the virus to no longer use the cell to carry out its life cycle
Finally, a virus can leave the cell by fusing with its plasma membrane, known as extrusion, this process keeps the host cell alive, and allows the continued use of the host cell by the virus, a virus in this state is said to be in a productive cycle
What happens during the lytic cycle?
The virus maximizes the use of the cells machinery with little regard for the survival of the host cell, once swollen the cell lyses, viruses in the lytic phase are termed virulent
In the event that the virus does not lyse the bacterium in the lytic cycle what happens?
It may integrate into the host genome as a provirus or prophage, initiating the lysogenic cycle replicating the virus as the bacterium reproduces because it is now a part of the hosts genome
How can environmental factors cause the cell to revert back to a lytic cycle from a lysogenic cycle?
By causing the provirus to leave the genome
How can integration of the phage into the host genome actually benefit the bacterium?
Infection with one strain of phage generally makes the bacterium less susceptible to superinfection (simultaneous infection with other phages)
What are prions and viroids? (Very broad definition)
Very small particles that can cause disease under certain circumstances
What are prions? And what do they do?
Prions are infectious proteins, non living, cause disease by triggering missfolding of other proteins, usually though the conversion of a protein from a helical structure to a B-pleated sheet
This drastically reduces solubility of the protein, and ability of the cell to degrade the protein, eventually the protein aggregates form, interfering with cell function
Main disease prions are known to cause?
Bovine spongiform encephalopathy (mad downs disease) destroying the brain and spinal cord
What are viroid? What do they do?
Viroids are small pathogens consisting of a very short circular single-stranded RNA that infects plants
Viroids can bind to large numbers of RNA sequences and can silence genes in the plant genome, preventing synthesis of necessary proteins, resulting in metabolic disruption and structural damage to the cell
Few examples of human viroids exits
