Chapter 1 - Cell Theory, Bacteria & Viruses

Question 1

What does the cell theory say?

Answer 1

– All living things are composed of cells
– The cell is the basic functional unit of life
– Cells arise only from pre-existing cells
– Cells carry genetic information in their DNA

Question 2

Differences between prokaryotes and eukaryotes

Answer 2

– Prokaryotes don’t have complex membrane bound organelles in their cytoplasm
– Prokaryotes don’t have a complex cytoskeletal system as eukaryotes do
– prokaryotes don’t have a nucleus/nuclear membrane that surrounds the DNA
– Prokaryotes are unicellular, while eukaryotes can be unicellular or multicellular
- prokaryotes reproduce asexually by binary fission whereas eukaryotes reproduce sexually
-Prokaryotes can undergo transcription and translation simultaneously, while eukaryotes can’t ‘
-In prokaryotes, ATP is generated by oxidative phosphorylation in the plasma membrane; in eukaryotes oxidative phosphorylation occurs in the mitochondria
-Prokaryotes have operons, promoter sequences which control the production of multiple genes

Question 3

Compare mitochondrial DNA and nuclear DNA

Answer 3

Non-nuclear DNA is found in the mitochondria, it is haploid (maternal copy only), circular shaped forming a circle.
Nuclear DNA is found in the nucleus, it is diploid (when do maternal when one paternal copy), and it is linear.

Question 4

Similarities between eukaryotes and prokaryotes

Answer 4

– Both have selectively permeable plasma membranes
– Prokaryotes have cell walls and eukaryotic plant cells have cell walls
– Both have ribosomes and DNA as genetic material
– Both have similar mechanisms for transcription and translation
-Both have retrotransposons

Question 5

In prokaryotes, the single circular chromosome is present in a structure called the _______

Answer 5

Nucleoid which has no boundary membrane

Question 6

Describe the nuclear membrane/envelope and its function.

Answer 6

It is a double membrane that maintains an environment in the nucleus distinct from the cytoplasm. There are holes in the membrane called nuclear pores, which allow selective two way exchange of material between the cytoplasm and the nucleus.

Question 7

What is the nucleolus?

Answer 7

It is located in the nucleus, taking up 25% of the space. It is responsible for synthesizing ribosomal RNA.

Question 8

Mitochondria structure

Answer 8

Has two membranes: inner and outer. Outer membrane serves as barrier between cytosol and inner environment while inner membrane is arranged into numerous folding called cristae.

Question 9

What is the function of the inner membrane in mitochondria?

Answer 9

The inner membrane contains cristae which contain the molecules and enzymes of the ETC.

Question 10

The endosymbiotic theory

Answer 10

Says that membrane bound organelles in cells evolved from aerobic prokaryotes that were engulfed by a larger prokaryote bacteria. The two prokaryotes formed a symbiotic relationship this way. Organelles that have their own DNA such as mitochondria and chloroplasts are said to have developed according to this theory.

Question 11

What is the function of lysosomes

Answer 11

Membrane bound organelles having an acidic pH of 5, it digests cell parts by releasing hydrolytic enzymes, fuses with phagocytotic vesicles to break them down, and participates in cell death by releasing enzymes into the cytosol

Question 12

How are lysosomes formed?

Answer 12

They are formed when budding off of the Golgi apparatus.

Question 13

What are endosomes?

Answer 13

They are membrane bound vesicles in charge of regulating the trafficking of proteins and lipids to and from the membrane. They are responsible for transporting materials to the trans Golgi, to the cell membrane, or to the lysosomal pathway for degradation.

Question 14

Rough ER

Answer 14

Interconnected membranes that are continuous with the nuclear envelope, and contain ribosomes on their membrane. Some protein synthesis occurs in the rough ER in the attached ribosomes.

Question 15

Proteins that are synthesized on ribosomes in the RER, travel to what destinations after synthesis?

Answer 15

Either stay in the ER, go to the Golgi, lysosome, endosomes, the plasma membrane, or are secreted outside of a cell.

Question 16

Proteins that are destined to stay in the cytosol are synthesized where?

Answer 16

They are synthesized in the free-floating ribosomes in the cytosol.

Question 17

What is the function of the smooth ER?

Answer 17

It is the site of lipid synthesis and detoxification of certain drugs and poisons.

Question 18

What is the function of the Golgi apparatus (endomembrane system)?

Answer 18

Made up of stacked membrane-bound sacs, the Golgi specializes in modifying proteins with the addition of groups like carbohydrates, phosphates, and sulfates. It introduces signal sequences, sorts the protein, and repackages it into vesicles which are directed to the correct cell location.

Question 19

What is the function of peroxisomes?

Answer 19

Vesicles which contain hydrogen peroxide that helps to break down long chain fatty acids via beta-oxidation. Also help in synthesis of phospholipids.

Question 20

What are the four types of tissue?

Answer 20

Epithelial, tissue, connective, tissue, muscle, and nervous tissue

Question 21

Functions of epithelial tissue

Answer 21

• Cover the body and line cavities
• protect against pathogen invasion and desiccation
• make up the functional identity of a lot of organs in the body like the nephrons and hepatocytes
• involved in absorption, secretion, and sensation

Question 22

How are epithelial cells organized in the tissue?

Answer 22

They are joined tightly together to an underlying layer of connective tissue called the basement membrane. They are also polarized, one side faces a lumen/inside of organ, while the other side interacts with underlying blood vessels and the rest of the body.

Question 23

Epithelial tissue can be classified according to layers

Answer 23

Number of layers:
Simple - one layer of cells
Stratified - multiple layers of cells
Pseudostratified - appears to have multiple layers, but only 1 in reality bc of different cell heights

Question 24

Epithelial cells classified into different shapes:

Answer 24

Cuboidal - cube
Columnar - long & thin
Squamous - flat and scale-like

Question 25

Functions of connective tissue

Answer 25

Provides framework for epithelial cells to carry out their functions, builds support structure such as bone, cartilage, tendons, ligaments, adipose tissue, blood, dermis, lymphatic tissue, etc.

Question 26

Prokaryotes are further divided into 2 domains:

Answer 26

Archaea and Bacteria

Question 27

Characteristics of Archaea

Answer 27

• They are single celled organisms which are physically similar to bacteria, but metabolically and gene wise are similar to eukaryotes.
• Many extremophiles make up archaea, but they also are present in the human body.
• Archaea use alternate energy sources from inorganic compounds like ammonia and sulfur
• They divide by binary fission and contain a single circular chromosome
• DNA is wrapped in histones

Question 28

Characteristics of bacteria

Answer 28

-Have a cell membrane, cell wall, cytoplasm, ribosomes, and plasmids
- Some have flagella
- Most abundant living organism on Earth

Question 29

Bacteria organized by shape:

Answer 29

Cocci - circle shaped
Bacilli - rod shaped
Spirili - spiral shaped (rare)

Question 30

Bacteria organized by cell wall type:

Answer 30

Gram positive - stains purple, consists of a thick cell wall with peptidoglycan, a polymeric substance made from amino acids and sugars
Gram negative - stains red, thin cell wall with very small amount of peptidoglycan, but contains an outer membrane w/ phospholipids and lipopolysacccharides which triggers a stronger immune response in the body than in gram positive bacteria

Question 31

Structure of flagella in bacteria

Answer 31

The tail is composed of the tip, filament (hollow structure composed of flagellin), hook, and basal body (complex motor structure anchored to the plasma membrane which rotates).
The hook connects filament to the basal body motor, serves as a bridge.

Question 32

What is the purpose of plasmids in bacteria?

Answer 32

Small circular structures in bacteria that are not necessary for survival, but they carry genes/DNA that confer antibiotic resistance. They also can carry virulence factors or traits that increase pathogenicity, such as toxin production or features that allow invasion of the host immune system.

Question 33

Compare the organization of DNA in bacteria and Archaea

Answer 33

In Archaea DNA is wrapped in histone proteins just like eukaryotes.
In bacteria, there are no histone proteins, but there are similar proteins that some bacteria have which organize the DNA.

Question 34

Describe the process of binary fission

Answer 34

Fast, simple form of asexual reproduction where the circular chromosome replicates in the bacterial cell, attaches to the plasma membrane as the cell grows and starts to form a cleavage furrow in the middle and then divides.

Question 35

Bacteria undergo genetic recombination that is there DNA is able to change to permit the evolution of the species overtime. What are the three ways that genes recombine in bacteria?

Answer 35

Transformation, conjugation, and transduction

Question 36

What is transformation?

Answer 36

It is when the bacteria takes in foreign genetic material from the outside and integrates these fragments into its host genome. This is common in gram-negative rods.

Question 37

What is conjugation?

Answer 37

It is known as the bacterial form of sexual reproduction. Cells which have a sex plasmid known as the fertility factor are the donors. The ones which don’t have it are recipients. The process goes like this:
1. A long pilus is formed on the donor that is made of sex pili.
2. It connects to the recipient forming a conjugation bridge.
3. Then, the donor which formed the pilus replicates its sex factor plasmid which then is transferred to the recipient along with other plasmid types through the bridge.
4. Important thing is that the DNA is always transferred from donor to the female.

Question 38

What is transduction?

Answer 38

The process of transferring genetic material from a virus into cells. An example is when a bacteriophage (a virus that infects bacteria) accidentally incorporates host DNA during assembly and when it infects another bacteria, it releases this trapped DNA into the new host cell.

Question 39

True or false:
Bacteria do not grow exponentially infinitely, they go through different phases of growth.

Answer 39

True. They go through different phases according to the environment.
1. Lag phase - When introduced in a new environment, bacteria have to first adapt to the conditions, so they don’t as fast.
2. Exponential phase - when the bacteria have adapted, the rate of division increases exponentially.
3. Stationary phase - as resources run out, bacterial growth starts to slow down.
4. Death phase - this marks the phase when resources are depleted, causing bacterial growth to decrease exponentially.

Question 40

What are viruses made of?

Answer 40

They all have genetic material (can be single or double stranded and either DNA/RNA) surrounded by a protein coat known as a capsid. This capsid can also be enveloped with phospholipids, but it makes the virus easier to kill because the envelope is sensitive to heat.

Question 41

Describe the structure of a bacteriophage.

Answer 41

Viruses that have a protein coat and nuclei acid as the head and a tail sheath extending from it with tail fibers that look like legs. The tail sheath acts as a syringe injecting DNA into the host bacteria, while the fibers allow attachment to the correct bacterial cell.

Question 42

Why are viruses not considered living organisms?

Answer 42

They are not living organisms because they cannot reproduce DNA on their own. They must use a host cell because they lack ribosomes to carry out proteins synthesis.

Question 43

AAMC FL1 Bio #44

Answer 43

Must know the definition of obligate parasites which are organisms that cannot complete their life cycle/reproduce without using a host
Example: any type of viruses
Application to problem: Answer is A because the agar plate only contains bacteria, animal viruses can’t replicate on the plate because their necessary host (animals) are not present. Animal viruses can’t infect bacteria.

Question 44

What is chemotaxis?

Answer 44

It is the ability of a cell to detect chemical stimuli and move toward or away from the stimuli.

Question 45

What type of genetic recombination do bacteriophages contribute?

Answer 45

Transduction because when they use a bacterial’s cell machinery to replicate themselves/their DNA, they also integrate some of the bacterial DNA into their own viral genome. Then, when these bacteriophages go onto infect other bacteria, they “accidentally” insert both their viral recombinant DNA with the bacterial DNA fragments incorporated inside.

Question 46

What function do bacteriophages have?

Answer 46

They are viruses which infect bacterial cells by taking over the bacterial cell’s machinery to replicate their own DNA and make more bacteriophages.

Question 47

What are retroviruses?

Answer 47

They are enveloped, ss RNA viruses which contain 3 enzymes called reverse transcriptase, integrase, and protease. They reverse transcribe their RNA genome into DNA in the host bacterial cell and then integrate their DNA into the host’s genome, where it is replicated & then transcribed by host ribosomes.
-Reverse transcriptase uses RNA dependent DNA polymerization

Question 48

What is virus-host specificity?

Answer 48

It means that viruses can only infect a specific set of host cells, because they must bind to specific receptors on the host cell.

Question 49

What are the steps of a general virus life cycle?

Answer 49

1. Infection - Once a virus binds to the correct receptor, depending on the virus type:
   *Enveloped virus fuses with plasma membrane, other viruses enters via endocytosis, or don’t enter at all like a bacteriophage and insert their DNA via their tail sheath
2. Translation & Assembly of viral particles
   *Viral DNA enters nucleus and is transcribed into mRNA —> mRNA goes into cytoplasm & is translated via the host’s ribosomes
   *The new capsid proteins and viral DNA/RNA assemble into virions in the cytoplasm
3. Release of the progeny/virions
   
   • There are multiple ways the virions are released such as:
     Cell death is initiated and virions are spilled
     The host cell lyses due to large number of virions
     Extrusion - The virion fuses with the cell membrane and leaves

Question 50

What is the lytic cycle?

Answer 50

This is when the bacteriophage utilizes the host cell’s machinery and after reproducing many new virions the cell lyses, releasing the virions and dies.

Question 51

What are virulent viruses?

Answer 51

These are viruses that undergo the lytic cycle.

Question 52

What is the lysogenic cycle?

Answer 52

This is when the bacteriophage doesn’t lyse the host cell, but instead integrates into the host genome as a provirus. That way every time the bacteria replicates, the provirus replicates with it and at any moment radiation or chemicals can trigger the provirus to leave the genome and start a lytic cycle, lysing out of the bacteria.

Question 53

What are prions?

Answer 53

They are small misfolded proteins (nonliving) that cause misfolding of other proteins. Usually alpha helices will misfold into beta sheets.

Question 54

What are viroids?

Answer 54

-Small pathogens consisting of short circular ssRNA that infects plant cells by silencing gene expression.
-No capsid or outer envelope
-There is one case where human viroids exist called the “hepatitis D virus”.

Question 55

Single stranded RNA viruses can be further divided into positive sense and negative sense. Explain the difference between these.

Answer 55

For positive sense viruses, the ss RNA in the viral genome acts as an “mRNA” and once it enters the host cell, it’s directly translated into viral proteins.

For negative sense viruses, once they enter the host, a new complementary mRNA strand must first be transcribed in the host cell nucleus by an RNA dependent RNA polymerase. This new cRNA is then translated to form the proteins necessary for viral assembly.

Question 56

What is a disease known to be caused by prions?

Answer 56

Mad cow’s disease (bovine encephalopathy)

Question 57

Life cycle of HIV Retrovirus

Answer 57

1. Envelope virus binds to CD4 & CCR5 proteins on the cell surface.
2. The enveloped virus fuses with the plasma membrane and empties out its viral contents.
3. Reverse transcriptase copes the RNA into dsDNA
4. The dsDNA integrates itself into the host’s DNA with the help of integrate
5. The host cell machinery transcribes its genome along with the viral genes
6. The viral mRNA exits nucleus and goes to a cytosolic ribosome where it is translated into necessary viral proteins
7. Viral proteins start to assemble and bud off the plasma membrane in a vesicle which forms the protein envelope of the virus itself
8. Protease cleaves the viral proteins further to make the virus mature and ready to infect a new cell

Question 58

How does mitochondria replicate in the cell?

Answer 58

Mitochondria has the ability to replicate through binary fission.

Question 59

A centrosome is composed of two ________

Answer 59

Centrioles (which are made of tubulin) oriented at right angles to each other

Question 60

Does gram positive or gram-negative bacteria contain two cell membranes?

Answer 60

Gram-negative bacteria contain 2 cell membranes. One membrane is inside the cell wall itself and the other is outside the cell wall.

Question 61

Endospores are only made by some ______________ bacteria.

Answer 61

Gram-positive

Question 62

What are endospores and what are their function?

Answer 62

They are states of which bacteria can enter into under harsh conditions to protect against desiccation, heat, cold, UV radiation, etc. Sometimes lack of necessary carbon or nitrogen can cause bacteria to become endospores. Bacteria can leave the endospore state and return to a vegetative state.

Question 63

Examples of epithelial tissue

Answer 63

The endothelium of blood and lymph vessels, and the mesothelium that lines thoracic and abdominal cavities.

Question 64

What is a vaccine and the purpose of it?

Answer 64

An inactive virus or portion of a virus that is delivered to a person so that their immune system can develop antibodies against the virus without contracting an actual viral infection.