Biology Chapter 2: Cellular Biology Flashcards
nuclear lamina
dense, fibrous network of intermediate filaments and proteins lining the inner nuclear membrane, providing structural support to the nucleus and anchoring chromatin.
Which intermolecular process primarily drives the formation of a bilayer when phospholipids are added to water?
Formation of bilayer is driven by entropy. Adding phospholipids to water decreases entropy because it forces water to arrange in an ordered, unfavourable cage-like structure (called a clathrate cage). Forcing lipids into a bilayer reduces this effect, increasing entropy (favorable)
Cyclins
regulatory proteins that control the progression of the cell cycle by activating cyclin-dependent kinases (CDKs) at specific checkpoints
Difference between totipotent, pluripotent and multipotent
Totipotent cells can form all body and extra-embryonic tissues, pluripotent cells can form all body tissues but not extra-embryonic tissues, and multipotent cells can differentiate into a limited range of cell types within a specific lineage.
Extra-embryonic: refers to tissues that support the development of the embryo but do not become part of the body of the organism itself. These include structures like the placenta, amniotic sac, and yolk sac
In translation, ribosomes read mRNA in what direction? What order is the protein synthesized?
mRNA is read in the 5’ to 3’ direction by the ribosome. Protein synthesized in the N->C direction
In DNA replication, DNA polymerase reads the template strand in what direction? And what direction is the new mRNA synthesized?
DNA polymerase reads the template strand in the 3’ → 5’ direction.
It synthesizes the new DNA strand in the 5’ → 3’ direction.
Which direction does mRNA polymerase read the template strand (anti-sense strand) and which direction is the resulting mRNA produced?
RNA polymerase reads the template strand (antisense strand) in the 3’ → 5’ direction.
It synthesizes the mRNA strand in the 5’ → 3’ direction.
Therefore, the mRNA is identical to the coding strand (the strand that isn’t transcribed) except mRNA has U instead of T
What is a 5’ cap?
Consists of a guanine nucleotide connected to the primary mRNA transcript via an unusual 5’ to 5’ triphosphate linkage. This guanosine residue is methylated at the 7 position directly after capping
The start codon for translation is positioned in what site of the ribosome during initiation?
The P position (peptidyl position)
The A site of a ribosome does what?
Binds incoming aminoacyl-tRNA carrying the next amino acid
The peptide chain grows from what position on a ribosome?
The P (peptidyl) position
What is contained in a complete culture medium?
The complete growth medium recommended for certain cell lines requires additional components which are not present in the basal medium and serum. These supplements help sustain proliferation and maintain normal cell metabolism and can include hormones, growth factors, and signaling molecules required for normal growth.
Nuclear export signals
are short sets of 4 hydrophobic residues in a protein that target the protein for export from the cell nucleus to the cytoplasm through the nuclear pore complex using nuclear transport
A nuclear localization signal
is an amino acid sequence that tags a protein for import into the cell nucleus by nuclear transport
Enzyme that creates a double-stranded DNA molecule from a single-stranded RNA molecule
Reverse transcriptase
Describe how reverse transcriptase works
creates a double-stranded DNA molecule from a single-stranded RNA molecule.
The single stranded RNA genome is first used as a template to create a double-stranded DNA-RNA hybrid.
The RNA is then degraded and the resulting single stranded DNA is used as a template to create double-stranded DNA.
True or false: prokaryotes have a cell wall
True
Are bacteria prokaryotes?
YES
Prions
is a type of misfolded protein that can cause other normal proteins in the body to misfold as well, leading to the formation of harmful aggregates. Unlike viruses or bacteria, prions do not contain DNA or RNA—they are made entirely of protein
Natural cellular response to the presence of misfolded proteins
production of heat shock proteins, which help to properly fold the defective protein molecules.
True or false, bacteria lack introns
True. For the most part, bacteria (prokaryotes) lack introns, whereas large eukaryotic genes usually contain several introns.
Difference between glycoprotein and a glycolipid
Glycoprotein = protein that spans the full membrane and involved in cell trafficking - ie CD-4.
Glycolipids act to provide energy and also serve as markers for cellular recognition. They typically don’t span all the way through the membrane. IE Gangliosides: Found in neuronal cell membranes and involved in signal transduction.
Which components of cells are physically connected by a gap junction?
The cytoskeleton of one to the cytoskeleton of the other
why chemical synapses are slower than electrical synapses?
Ribosomes are made of
are made of ribosomal RNA (rRNA) and ribosomal proteins, forming two subunits that work together to synthesize proteins.
Apoptosis vs Necrosis
Apoptosis = controlled and programmed cell death
necrosis = unplanned cell death and often causes inflammation
Cytochrome C
is a heme protein crucial for both energy production, as an electron carrier in the mitochondrial electron transport chain, and apoptosis, where its release from mitochondria triggers caspase activation and programmed cell death
Which of the following recombinant processes depends on the F factor plasmid?
Conjugation. It requires special genes for the pilus and these are usually present on a plasmid, a separate extragenomic strand of DNA not incorporated into the bacterium’s own DNA. This plasmid is referred to as the fertility or F factor.
Difference between prokaryote and eukaryote in protein synthesis?
Prokayotes = polycistronic
Eukaryotes = monocistronic
What cell would be the least likely to spend most of its time in G0?
Epithelial cells because they regenerate quickly
Endothelial cells vs epithelial cells
- Epithelial cells typically form barriers in skin, organ linings, and glands.
- Endothelial cells specifically line blood vessels, and in the brain, they have tight junctions that prevent harmful substances from crossing into the central nervous system.
HIV is an example of what kind of virus
Retrovirus
Retrovirus
Convert RNA to DNA using reverse transcriptase. It’s a type of ssRNA
Obligate intracellular parasitic particles,
Viruses. meaning they must hijack host cells to replicate
Are viruses prokaryotes
No - they rely on host cells to survive and replicate
What is a bacteriophage?
is a type of virus that infects bacteria. It hijacks bacterial cells to replicate itself, often killing the bacteria in the process. Bacteriophages are among the most abundant and diverse biological entities on Earth.
Enveloped vs non enveloped viruses
Enveloped viruses have a lipid membrane (envelope) derived from the host cell’s membrane. This envelope surrounds the viral capsid (protein shell) and helps the virus infect host cells.
What does hand washes do to the viral envelope
Easier to destroy – The lipid envelope is sensitive to detergents, alcohol, and soap, which disrupt the membrane and inactivate the virus.
protein coat on virus
Capsid. protein coat that surrounds and protects a virus’s genetic material (DNA or RNA)
Difference between virus and virion
A virus is a broad term referring to the entire entity, including its genetic material, structure, and ability to infect a host.
It exists both inside and outside a host cell.
A virion is the fully assembled virus complete with nuclear material inside a capside, extracellular form of a virus.
It is the infectious unit that exists outside the host, ready to infect new cells.
Size of virus
20 - 400nm
Order phases of bacterial growth
Lag phase, log phase, stationary phase
Types of horizontal gene transfer between prokaryote cells
Transformation, transduction and conduction
Frederick Griffith showed that harmless strains of Streptococcus pneumoniae exposed to virulent bacteria lysed with heat could become virulent themselves.
Which means of gene transfer did this experiment demonstrate?
Transformation
Why does HIV only transmit in bodily fluids?
Because it’s an enveloped virus and can’t survive on it’s own outside the body
enveloped viruses, including HIV, acquire their envelope from the host cell’s plasma membrane.
Four types of Viral Genomes
ssDNA, dsDNA, ssRNA and dsRNA
ssRNA can be split into
positive sense RNA and negative sense RNA
Positive sense RNA
is ssRNA that can be directly translated into protein (it’s like mRNA)
negative sense RNA
ssRNA complementary to mRNA
it has to be turned into mRNA by RNA replicase first before translation into protein
Life cycle of a virus - DNA viral genome
1) viral DNA translocates to nucleus
2) transcribed by RNA polymerase
3) Infected cell destroyed through lysis, releasing the virions
OR
Can be incorporated into host cell DNA and replicated when the host cell divides. Can be released through extrusion
Life Cycle of RNA viral genome
1) Genetic material must first be reverse-transcribed into DNA before integration (reverse transcriptase
Bacteriophages have 2 distinct life cycles
Lytic and lysogenic
Lytic cycle
Bacteriophage works to replicate at full speed, making use of the host cell’s machinery. Host cell fills with virions and lyses - releasing lots of virions
Lysogenic cyle
Integration of viral genetic material into host genome
Viroids
RNA particles that infect plants
Circular ssRNA sequences
Prions
Misfolded proteins that cause other proteins to misfold
Protozoa
(eukaryotes) single-celled parasites ie plasmodium (carried by mosquitos that cause malaria)
Helminths
Multicellular worms
Ectoparasites
multicellular parasites that live outside the host like lice and fleas
Parasitic infection targeted by what immune response
eosinophils and IgE antibodies
Examples of prokaryote gene expression
lac operon and trp operon
Types of operon control
Positive (activator stimulates transcription)
Negative (repressor prevents transcription by binding to the operator upstream of the first coding region
lac operon is under what kind of control?
Both positive and negative
Negative control of the lac operon
Inducible. meaning the repressor is always present but is removed in the presence of lactose.
lac operon is for if the cell is low on glucose and needs an alternative energy source
Positive control of the lac operon
When glucose is low, there is high levels of cAMP. cAMP binds to the CAP sequence, increasing transcription
What happens when there is high glucose and lactose is present?
1) repressor is removed
2) gene is expressed at low levels
What happens when there is low glucose and lactose is present?
1) repressor removed
2) cAMP binds to CAP
very high levels of gene expression
What happens when there is high glucose and lactose isn’t present?
1) repressor is on the operator
No expression
What happens when there is low glucose and lactose isn’t present?
1) repressor is on the operator
2) cAMP binds to CAP
No expression
What kind of negative control does the trp operon use?
Repressible. High levels of trptophan inhibits the operon
Promoters
Found in both prokaryotes and eukaryotes. Upstream regions that initiate transcription
Examples of promoters
TATA Box, CG Box, CAAT Box
Enhancer
is a regulatory DNA sequence that increases transcription by binding transcription factors and looping the DNA into a hairpin-like structure, bringing the enhancer physically closer to the promoter to help recruit RNA polymerase.
only in eukaryote cells
Silencer
regions of DNA to which transcription factors known as repressors bind
miRNA and siRNA both
silence genes by interrupting expression between transcription and translationn
What does it mean for a virus to have a +ssRNA genome?
+ssRNA can be directly translated into proteins by host ribosomes.
Examples: Poliovirus, SARS-CoV-2, Dengue virus.
Exception: Retroviruses (e.g., HIV-1) have +ssRNA but do not translate it directly; they first convert it into DNA via reverse transcriptase.
Why can’t retroviruses (e.g., HIV-1) directly translate their +ssRNA genome?
Retroviruses carry +ssRNA, but they must first convert it into DNA using reverse transcriptase (RT).
The dsDNA integrates into the host genome via integrase (IN).
Only after integration does the host transcribe viral mRNA for translation.
This process makes retroviruses unique among +ssRNA viruses.
Hallmark for retroviruses
they must integrate their genetic material into the host genome for replication
Pore-forming toxins (exotoxins)
proteins produced by bacteria that create holes in cell membranes. These toxins are virulence factors that help bacteria evade the immune response of their hosts and promote infection
Histone acetylation happens on what structure?
lysine residues of histone proteins, not directly on DNA. It’s a post-translational modification of the histone protein
Histones have what kind of charge
Positively charged
Histone acetylation makes the histone
Histone acetylation makes the histone less positive, and exposes more DNA for transcription
Kinetochores
protein structures that attach chromosomes to spindle microtubules during cell division. They are essential for proper chromosome segregation
directs a protein to the endoplasmic reticulum (ER), where it enters the secretory pathway for secretion or insertion into the cell membrane.
a signal sequence directs a protein to the endoplasmic reticulum (ER), where it enters the secretory pathway for secretion or insertion into the cell membrane.
Is the coding strand the template strand?
NO - Template strand is the non coding strand
Do Bacteria Have Sterols Like Eukaryotes?
No, most bacteria do not contain sterols (like cholesterol), which are commonly found in eukaryotic membranes.
Most bacteria lack sterols because they have a rigid cell wall (peptidoglycan) that provides structural support.
peptidoglycan
is a mesh-like polymer of sugar chains (NAG and NAM) cross-linked by peptides that forms the bacterial cell wall, providing structural support and protection.
Do Bacteria Have Glycolipids?
❌ Most bacteria do not contain glycolipids in their cytoplasmic (inner) membrane.
✅ Some bacteria have glycolipid-like molecules in their outer membrane, particularly Gram-negative bacteria.
Difference between eurkaryotes and prokaryotes: organelles
😺 Eukaryotes: Membrane-bound organelles (nucleus, mitochondria, ER, Golgi, etc.)
🦠 Prokaryotes: No membrane-bound organelles; everything occurs in the cytoplasm
Difference between eurkaryotes and prokaryotes: Nucleus
😺 Eukaryotes: True nucleus with a nuclear membrane
🦠 Prokaryotes: No nucleus; DNA is in a nucleoid region
Difference between eurkaryotes and prokaryotes: DNA Organization
😺 Eukaryotes: Linear chromosomes, packed with histones
🦠 Prokaryotes: Single circular chromosome, often no histones
Difference between eurkaryotes and prokaryotes: Cell Division
😺 Eukaryotes: Mitosis or meiosis
🦠 Prokaryotes: Binary fission (asexual reproduction)
Difference between eurkaryotes and prokaryotes: Ribosomes
😺 Eukaryotes: Large (80S) ribosomes (60S + 40S subunits)
🦠 Prokaryotes: Smaller (70S) ribosomes (50S + 30S subunits)
Difference between eurkaryotes and prokaryotes: Cell wall
😺 Eukaryotes: Only in plants (cellulose) & fungi (chitin)
🦠 Prokaryotes: Most have a peptidoglycan cell wall (except Mycoplasma)
Difference between eurkaryotes and prokaryotes: Membrane Lipids
😺 Eukaryotes: Contain sterols (e.g., cholesterol)
🦠 Prokaryotes: No sterols (except Mycoplasma, which steals them from host)
Difference between eurkaryotes and prokaryotes: Genetic Exchange
😺 Eukaryotes: Sexual reproduction via gametes (meiosis)
🦠 Prokaryotes: Horizontal gene transfer (transformation, transduction, conjugation)
Difference between eurkaryotes and prokaryotes: Respiration
😺 Eukaryotes: Occurs in mitochondria
🦠 Prokaryotes: Occurs in the plasma membrane (no mitochondria)
Difference between eurkaryotes and prokaryotes: Size
😺 Eukaryotes: Larger (10-100 µm)
🦠 Prokaryotes: Smaller (0.1-5 µm)
are specific proteins or DNA sequences that are used to identify certain regions or structures inside the nucleus of a cell. help scientists determine the position of genes, proteins, or other molecules within the nucleus.
Nuclear markers
How bacteria become resistant to antibiotics
Through mutations
Does lower or higher IC50 mean MORE toxic?
Lower values (ie less concentration of X can kill 50% of the population)
transcription factors
Transcription factors are proteins that regulate gene expression;
endosymbiotic bacterium
is a bacterium that lives inside a host organism’s cells in a mutually beneficial or dependent relationship.
Porins
are channel proteins in the outer membrane of Gram-negative bacteria, mitochondria, and chloroplasts that allow the passive diffusion of small molecules, including nutrients, waste, and some antibiotics, impacting bacterial susceptibility to drugs.
difference between lytic and lytogenic cycle
The lytic phase/cycle can be contrasted with the lysogenic cycle, during which the virus does not kill the infected bacterium. These two cycles are shown below.
can non enveloped viruses survive on their own outside the body?
YES, like the common cold
Differences between +ssRNA and -ssRNA viral genomes
(+ssRNA viruses) → Can be directly translated.
(-ssRNA viruses) → Must be converted into mRNA first.
Difference between dsDNA and ssDNA viral genomes
dsDNA viruses → Can be transcribed directly into mRNA.
ssDNA viruses → Must be converted into dsDNA first before transcription.
Retroviruses are what kind of viral genome?
+ssRNA
Reverse transcriptase (RT) is only used by retroviruses, which are +ssRNA viruses that follow a completely different replication strategy. These viruses, such as HIV, use RT to convert their RNA genome into dsDNA, which then integrates into the host genome.
Retrovirus Steps (e.g., HIV):
(+ssRNA) → Reverse transcription (via RT) → dsDNA
dsDNA → Integration into host genome (via integrase)
Transcription (by host RNA polymerase) → mRNA
mRNA → Translation → Viral proteins
Reverse Transcriptase is Used by Retroviruses, Not RNA Viruses in General
Use RNA-dependent RNA polymerase (RdRp) to transcribe mRNA
dsRNA
apoptotic signaling means cells are stopping
growth
Are operons alternatively spliced?
No! because there are no introns
Answer is A
Nearly 95% of the human genome does not code for proteins or RNA. In contrast, the genomes of both prokaryotes and unicellular eukaryotes largely lack introns. In these organisms, most genetic material does code for protein products.
cell cycle order
G1/M/G2/S
Aster
Asters help position the spindle, anchor the centrosomes, and guide proper cell division—basically acting like the structural GPS of the dividing cell.
