MCAT - Biology Flashcards
This deck was created by combining two or more decks
Facilitated Diffusion
Makes the membrane selectively permeable because it is able to select between molecules of similar size and charge. Must occur down the electro-chemical gradient of all species involved.
Fluid Mosaic Model
Since the forces holding the entire membrane together are intermolecular, the membrane is fluid; its parts can move laterally but cannot separate. This is reflected in the asymmetrical layout of the integral membrane proteins.
-> In eukaryotic membranes, cholesterol moderates membrane fluidity (prokaryotic -> hopanoids).
Smooth ER
Distal to the nucleus. The site of lipid synthesis including steroids. Helps to detoxify some drugs.
Peroxisomes
Vesicles in the cytosol. Grow by incorporating lipids and proteins from the cytosol. Self-replicate instead of budding off of other membranes. Involved in the production and breakdown of hydrogen peroxide. Inactivate toxic substances such as alcohol, regulate oxygen concentration, play a role in synthesis and breakdown of lipids and in the metabolism of nitrogenous bases and carbohydrates.
Mitochondria
Have their own circular DNA. Antibiotics that block translation by prokaryotic ribosomes but not eukaryotic ribosomes also block translation by mitochondrial ribosomes. Mitochondria are inherited from the mother. Have an inner and outer membrane.
Cristae
The internal compartments formed by the inner membrane of the mitochondria. Studded with proteins including ATP synthase and a variety of cytochromes. Increases surface area for chemical reactions, where cellular respiration (aerobic since mitochondria require oxygen) occurs.
Interstitial Fluid
Fluid between the cells.
Glycolysis
First stage of aerobic and anaerobic respiration. Occurs in the cytosol.
Glucose + 2ADP + 2P(i) + 2H2O + 2NAD+ —> 2 pyruvate + 2ATP + 2NADH
Can be performed by any cell (vs gluconeogenesis: formation of glucose from noncarbohydrate precursors - occurs mainly in the liver).
*The addition of a second phosphate to glucose commits it to the glycolytic pathway! (fructose 1,6-bisphosphate)
Fermentation
Anaerobic respiration. Includes glycolysis, reduction of pyruvate to ethanol (yeast) or lactic acid (human muscle cells), and oxidation of NADH back to NAD+.
Substrate-Level Phosphorylation
An energy-rich intermediate transfers its phosphate group to ADP, forming ATP, without requiring oxygen. As opposed to using energy from diffusion.
Ex: glyceraldehyde 3-phosphate (G3P or PGAL) in glycolysis, phosphocreatine in skeletal muscles
Cofactors
Metal ions or coenzymes that activate an enzyme by binding tightly to it.
Krebs (Citric Acid) Cycle
Aerobic respiration. The oxidation of glucose and reduction of oxygen (as the final electron acceptor –> H2O). Occurs in mitochondrial matrix (inside both membranes) with products of glycolysis (pyruvate and NADH). Once inside matrix, pyruvate is converted to acetyl CoA in a rxn that produces NADH and CO2. During the cycle, two carbons are lost as CO2 and oxaloacetic acid is reproduced to begin the cycle over again.
ATP is produced by substrate-level phosphorylation.
Glucose (C6H12O6) + 6O2 –> 6CO2 + 6H2O
(combustion rxn)
Produces 36 net ATP btwn cycle and ETC (and 2 from glycolysis).
One glucose produces two cycles. One cycle produces 1 ATP, 3 NADH, and 1 FADH2.
H from NADH and FADH2 go on to ETC, where O2 is reduced to H2O.
Can use:
- Triglycerides –> fatty acids –(-1 ATP)-> acyl CoA –(-2C)-> acetyl CoA
- Amino acids –(deamination in liver)-> deaminated pdt –> pyruvic acid or acetyl CoA
Oxidative Phosphorylation
The production of ATP via the electron transport chain and ATP synthase.
Organism Classification
- Energy source
- Phototrophs: light
- Chemotrophs: oxidation of organic or inorganic matter - Carbon source
- Autotrophs: CO2 exclusively
- Heterotrophs: organic matter
CO2 fixing: reducing it and using the carbon to create organic molecules
-> Only prokaryotes can acquire energy from an inorganic source other than light.
Prokaryote
No membrane bound nucleus; instead, have a single, circular double stranded molecule of DNA. Have nucleoids and ribosomes, just no complex, membrane bound organelles. No centrioles.
Split into two domains:
- Bacteria
- Archaea (have more in common with eukaryotes)
Nucleoid
Irregular shaped area inside a prokaryotic cell formed from the genetic material (DNA, RNA and protein complex) and serves as a nucleus. NOT membrane-bound.
AKA chromatin body, nuclear region, or nuclear body.
The Central Dogma (of gene expression)
All organisms use the same method of gene expression:
DNA –> RNA –> proteins
Nucleotide
Always made up of 3 parts:
1) Phosphate group
2) 5 C sugar
3) Nitrogenous base
DNA Structure
Nucleotides are held together by phosphodiester bonds between the 3rd C (3’) hydroxyl of one deoxyribose and the 5th C (5’) phosphate of another deoxyribose. The backbone of a single strand of DNA has 5’ -> 3’ directionality.
Purines
Two-ring structures: adenine and guanine.
Pyrimidines
One-ring structures: cytosine and thymine (and uracil).
think: pyrimidine has a ‘y’ and so do cytosine and thymine
Base-pairing
The hydrogen bonding between nitrogenous bases to form the double stranded structure of DNA.
A and T form 2 H bonds –> A2T
C and G form 3 H bonds –> C3G
(why complementary strands match up)
The length of a strand of DNA is measured in base-pairs (bp).
RNA
Identical to DNA in structure except that:
- C2 on the pentose sugar is not “deoxygenated” (has hydroxyl group attached).
- RNA is single-stranded.
- RNA contains the pyrimidine uracil instead of thymine (similarity between the two is a common cause of mutations).
DNA is produced by replication, RNA is produced by transcription.
In animals, DNA is only in the nucleus and mitochondrial matrix, RNA can move through nuclear pores so it is also in the cytoplasm.
3 types of RNA: mRNA, rRNA, tRNA
Messenger RNA (mRNA)
A form of RNA that carries the instructions for making a protein (amino acids) from a gene (DNA) and delivers it to the site of translation (cytosol).
Ribosomal RNA (rRNA)
RNA molecules that bind with proteins to form ribosomes as the site of translation of proteins (amino acids). rRNA is synthesized in the nucleolus (an area inside the nucleus, ribosomes are assembled; not separated by a membrane; disappears during prophase).
Transfer RNA (tRNA)
A single strand of RNA that sequesters the appropriate amino acids (dictated by mRNA) in the cytosol and transfers them to the site of translation (ribosomes) for incorporation into a protein.
Lagging Strand
New DNA strand whose polymerization is continuously interrupted and restarted with a new primer.
Leading Strand
The continuously-synthesized new strand of DNA.
Bidirectional Replication
All eukaryotic DNA replication begins at an origin of replication and continues along the chromosome in opposite directions.
Semiconservative Replication
When a new DNA strand is created, it contains one strand of the original DNA and one strand of newly synthesized DNA.
Nucleic Acid Hybridization
Complementary strands of nucleic acids will spontaneously bind in any combination:
DNA-DNA
DNA-RNA
RNA-RNA
–> Enables the identification of unknown nucleotide sequence by binding it with a known sequence.
Denaturization
To split the double helix of DNA into two strands.
5 Steps of Replication
Prokaryotes and eukaryotes:
- Helicase unzips the double helix.
- RNA primase builds a primer.
- DNA polymerase (III) assembles the leading and lagging strands.
- Primers are removed (DNA pol I).
- Okazaki fragments are joined (Ligase).
Very fast and accurate.
DNA Polymerase
The enzyme that builds the new DNA strand; requires an RNA primer on which to add new nucleotides.
Reads the parental strand 3’ -> 5’ (upstream) and creates the new complementary strand 5’ -> 3’ (downstream).
(Think: DNA is complicated to understand so reading it is like paddling upstream. Once it is read, creating it is downstream.)
Okazaki Fragments
The series of disconnected strands that make up the lagging strand.
Telomeres
Repeated six-nucleotide units that protect the chromosomes from being eroded through repeated rounds of replication.
Genetic Code
The amino acids and “start” and “stop” signals that are coded for by each of the 64 possible mRNA codons (4 possible nucleotides can be placed in each of 3 positions –> 4^3 = 64).
The genetic code is:
- Degenerative: more than one series of three nucleotides may code for any amino acid.
- Unambiguous: any single series of nucleotides will code for one and only one amino acid.
- Almost universal: nearly every living organism uses the same code.
RNA polymerase
A required enzyme that adds and links complementary RNA nucleotides during transcription.
Transcription
Process by which all RNA is manufactured from a DNA template (in nucleus or mitochondrial matrix where DNA is). 10x slower than replication.
- Initiation: requires a promoter (sequence of nucleotides) on the DNA strand to tell the RNA polymerase where to begin transcription (vs. primer in replication). RNA polymerase unzips the DNA double helix.
- Elongation: RNA polymerase transcribes only one strand of the DNA nucleotide sequence into a complementary RNA nucleotide sequence.
(RNA polymerase reads DNA 3’ -> 5’ and builds new RNA 5’ -> 3’ like DNA polymerase. No proof reading mechanism like replication but errors are not mutations, not as harmful.) - Termination: requires stop signal and proteins to separate RNA polymerase from DNA.
Primary Transcript
Initial mRNA nucleotide sequence arrived at through transcription. Processed post-transcriptionally in 3 ways:
- Addition of nucleotides.
- Deletion of nucleotides.
- Modification of nitrogenous bases.
Introns
Long segments of nucleotides that have no coding information; between adjacent genes. Remain in the nucleus. Intron sequences are generally much longer than exon sequences.
Exons
Portions of the gene that exit the nucleus to be translated (expressed) into proteins. May be spliced together in different orders to form different polypeptides.
snRNPs
Small nuclear ribonucleoproteins; enzyme-RNA complexes which recognize nucleotide sequences at the ends of introns. They loop the introns, bringing the exons together. Then they excise the introns and splice the exons together.
Post-Transcriptional Processing (of RNA)
Occurs in prokaryotes and eukaryotes.
Prokaryotes - occurs in all tRNA and rRNA, but almost all mRNA is directly translated to proteins.
Eukaryotes - occurs in each type of RNA and allows for additional gene regulation.
Complementary DNA (cDNA)
DNA that has been reverse transcribed from mRNA using reverse transcriptase. Adding DNA polymerase to cDNA produces a double strand of the desired DNA.
–> useful for cloning eukaryotic DNA with bacteria because bacteria have no mechanism for removing introns.
Translation
The mRNA transcribed from the DNA template brings the complementary genetic code to the cytoplasm to be read and made into proteins from the complementary amino acids.
- mRNA carries the genetic information from the nucleus to the cytoplasm in the form of codons.
- tRNA carries the complementary nucleotides (anticodons) and sequesters the amino acids that correspond to the anticodon.
- rRNA binds with proteins to make up the ribosome, which provides the site for translation to take place.
Ribosome
Site of translation. Made up of a small subunit and a large subunit of rRNA and many separate proteins.
–> synthesized by the nucleolus (not found in prokaryotes, although synthesis is similar). Ribosome is assembled in nucleolus but small and large subunits are exported separately to the cytoplasm.
Codon
A series of three-nucleotide sequences on the mRNA; each corresponds to an amino acid or signifies a “start” or “stop” signal for translation.
Anticodon
A three-nucleotide sequence on a tRNA that is complementary to an mRNA codon.
Start Codon
AUG
–> signals the beginning of protein synthesis.
Stop Codons
UAA, UAG, UGA
–> signal an end to protein synthesis.
Initiation
The first step of translation.
- 5’ of mRNA attaches to the small subunit of the ribosome.
- A tRNA possessing the 5’-CAU-3’ anticodon (to start codon 5’-AUG-3’ from mRNA) sequesters the amino acid methionine and settles in at the P site (peptidyl site).
- This signals the large subunit to join and form the initiation complex.
Elongation
The second step of translation; elongation of the polypeptide.
- A tRNA with its corresponding amino acid attaches to the A site (aminoacyl site) of ribosome at the expense of two GTPs.
- The carboxyl end of methionine attaches to the amine end of the amino acid in a dehydration reaction.
- Translocation: the ribosome shifts 3 nucleotides along the mRNA towards the 3’ end and the tRNA that carried methionine moves to the E site (exit site) where it can exit the ribosome. The tRNA carrying the newly formed dipeptide moves to the P site, clearing the A site for the next tRNA.
- -> requires the expenditure of another GTP
Elongation is repeated until a stop codon reaches the P site.
Termination
The third step of translation.
- A stop codon reaches the A site and proteins (release factors) bind to the A site allowing a water molecule to attach to the end of the polypeptide chain.
- The polypeptide is freed from the tRNA and ribosome, and the ribosome breaks up into its subunits to be used again later.
Post-Translational Modifications
Sugars, lipids, or phosphate groups are added to the amino acids; the polypeptide may be cleaved in one or more places; separate polypeptides may join to form the quarternary structure of a protein.
Signal Peptide
Directs a ribosome to attach to the rough ER. Without a signal, the ribosome remains floating in the cytosol. Depends on where the resulting protein will need to go.
Point Mutations
Mutation that changes a single base-pair of nucleotides in a double strand of DNA.
Base-Pair Substitution Mutation
One base-pair is substituted for another.
A-T –> C-G
C-G –> A-T
Missense Mutation
A base-pair substitution that changes the amino acid coding sequence of a gene to code for another amino acid.
Nonsense Mutation
A base-pair mutation that results in a stop codon. Prevents translation of a functional protein (serious).
Insertion or Deletion Mutation
Insertion or deletion of a base-pair, results in a frame shift mutation (when it occurs in multiples other than 3). Often result in a completely nonfunctional protein (vs. non-frame shift - may result in partially or even completely active protein).
Wild Type
The original state of an organism.
Forward Mutation
Shifts an already mutated organism further from its original state.
Backward Mutation
Shifts an already mutated organism back closer to its original state.
Nucleosome
Eight histones wrapped in the DNA.
Chromatin
The entire DNA-protein complex (many nucleosomes).
Chromosome
The chromatin associated with each of the 46 double stranded DNA molecules in human cells.
Homologues
Two chromosomes that code for the same traits but do not necessarily have the same genes (alleles).
- diploid: a cell with homologous pairs
- haploid: a cell without homologous pairs
Centromeres
A group of proteins located toward the center of the chromosome; where microtubules attach (to kinetochore protein -> kinetochore microtubules).
Chromatids
Identical sister sets resulting from chromosome (DNA) replication; attached at the centromere. The cell is still considered to have the same number of chromosomes.
Tetrads
When duplicated homologous chromosomes line up next to each other for a total of 4 chromatids.
Crossing Over
In prophase I, homologous chromosomes may exchange sequences of DNA (genetic recombination).
Chiasma
The single point where chromosomes are attached during crossing over.
Nondisjunction
When the centromere of any chromosome does not split during anaphase I or II.
Primary nondisjunction: anaphase I - all gametes affected. Two have an extra chromosome and two are missing a chromosome.
Secondary nondisjunction: anaphase II - half the gametes affected. One has an extra chromosome and one is missing a chromosome.
(can also occur in mitosis but consequences are not as severe since the genetic info in the new cells is not passed on to every cell in the body)
Chromosomal Deletion
Part of the chromosome breaks off or is lost during homologous recombination and/or crossing over.
–> can occur with entire chromosomes or even entire sets of chromosomes (nondisjunction).
Chromosomal Duplication
When a DNA fragment breaks free of one chromosome and is inserted in the homologous chromosome.
–> can occur with entire chromosomes or even entire sets of chromosomes (nondisjunction).
Inversion
Mutation when the orientation of a section of DNA is reversed on the chromosome.
Translocation
Mutation when a segment of DNA from a chromosome is inserted into a nonhomologous chromosome.
Transposable Elements (Transposons)
DNA segments that can excise themselves from a chromosome and reinsert themselves in a different location. Can contain one gene, several genes, or just a control element. Flanked by identical nucleotide sequences.
Transposition can cause translocation and inversion.
–> one mechanism by which a somatic cell of a multicellular organism can alter its genetic makeup without meiosis.
Centrosome
The major microtubule organizing center (MTOC) in mitosis in animal cells.
Centrioles
The barrel-shaped structures of microtubules arranged perpendicularly in the centrosome.
9 + 2 Microtubule Arrangement
The arrangement of microtubules in the axoneme of eukaryotic flagella or cilia. 9 pairs of microtubules form a circle around two lone microtubules. Dynein cross bridges connect each of the outer pairs of microtubules to their neighbor, which causes the microtubule pairs to slide past each other and move the flagella or cilia in a whip-like motion.
In humans, cilia are found only in the Fallopian tubes and respiratory tract.
Prokaryotes: flagella are made of a single strand of protein called flagellin and they move by rotation.
Asters
Microtubules radiating from the centrioles.
Kinetochore
A structure of protein and DNA located at the centromere of the joined chromatids of each chromosome.
Ionizing radiation can cause double stranded breaks in the DNA. Eukaryotes are able to repair some of these breaks, but prokaryotes are not. Which of the following gives the most likely explanation for this difference?
A. Prokaryotes do not possess a ligase enzyme to join the separated DNA molecules.
B. Prokaryotic DNA is single stranded.
C. Eukaryotes have matching pairs of chromosomes to act as a template for repair.
D. Eukaryotes have more DNA making the consequences of a break less severe.
Answer: C
Restriction Enzymes
Cut the nucleic acids according to palindromic nucleotide sequences. Usually cuts the DNA unevenly.
Recombinant DNA
Two DNA fragments that were cut by the same restriction endonuclease and can (artificially) recombine regardless of the origin of the DNA.
Probe
The radioactively labeled complementary sequence of the desired DNA fragment.
–> used in library screening.
Southern Blot
Used for detection of a specific DNA sequence in DNA samples. It combines transfer of electrophoresis-separated DNA fragments to a filter membrane and subsequent fragment detection by probe hybridization.
vs. Northern (RNA), Western (proteins - uses antibodies), etc.
Polymerase Chain Reaction (PCR)
A fast way to “clone” DNA. The method relies on repeated heating and cooling of the reaction for DNA denaturization and enzymatic replication of the DNA. Primers (short DNA fragments) containing sequences complementary to the target region along with a DNA polymerase (after which the method is named) enable selective and repeated amplification. As PCR progresses, the DNA generated is itself used as a template for replication, setting in motion a chain reaction in which the DNA template is exponentially amplified.
RFLP (Restriction Fragment Length Polymorphism)
Identifies individuals as opposed to specific genes.
DNA of different individuals possesses different restriction sites and different distances between restriction sites. After fragmenting a DNA sample with endonucleases, a band pattern unique to an individual is revealed on radiographic film via southern blotting.
–> RFLPs are the DNA tests used to identify criminals in court cases.
Operon
The genetic unit usually consisting of the operator, promoter, and genes that contribute to a single prokaryotic mRNA.
Lac Operon
The operon that controls the metabolism of lactose in E. coli.
Operator
The piece of DNA in the lac operon that overlaps the promoter site and serves as the on-off switch.
Repressor
A protein that binds to an operator and physically blocks the RNA polymerase from binding to a promoter site, stopping the transcription of the genes in the operon.
Vector
A DNA molecule used as a vehicle to transfer foreign genetic material into another cell.
Plasmid
Double-stranded, generally circular DNA sequences that are capable of automatically replicating in a host cell. Incubating bacteria with plasmids generates hundreds or thousands of copies of the vector within the bacteria in hours (transformation).
Screening
Not all bacteria in a library will have the vector and not all vectors will have the DNA. To screen for the appropriate bacteria, use the lacZ gene and an antibiotic resistant gene when originally preparing the clone. Use an endonuclease that will insert the DNA fragment into the middle of the lacZ gene and inactivate it.
- -> clones with an active lacZ gene turn blue in the presence of X-gal.
- -> clones without resistance to the antibiotic will be eliminated.
Bacteria Shapes
Cocci: round Bacilli: rod-shaped Spirilla: rigid helical-shaped Spirochetes: non-rigid helical-shaped -> certain species of spirochetes may have given rise to eukaryotic flagella through a symbiotic relationship.
–> name of bacteria often reveals its shape: spiroplasma, staphylococcus, pneumococcus, etc.
Bacterial Envelope
A cell wall on the exterior of the plasma membrane which prevents the protoplast (the bacterial plasma membrane and everything inside of it) from bursting since most bacteria are hypertonic. As the cell fills with water and the hydrostatic pressure builds, it eventually equals the osmotic pressure and the filling stops (equilibrium).
Peptidoglycan
A series of disaccharide polymer chains with amino acids, three of which are not found in proteins. The chains are connected by their amino acids or are crosslinked by an interbridge of more amino acids. Makes up the cell wall of bacteria from continuous chains that form a single molecular sac around the bacterium. More elastic than cellulose (plant cell wall). Porous so it allows large molecules to pass through. Many antibiotics (penicillin) attack the amino acid cross links. Cell wall is disrupted, cell lyses killing the bacterium. Lysozyme (enzyme produced by humans) attacks the disaccharide linkage. Cell wall is disrupted, cell lyses killing the bacterium.
Gram Staining
A staining technique used to prepare bacteria for viewing under the light microscope. Stains two major cell wall types differently:
- Gram-positive bacteria: the thick peptidoglycan cell wall prevents the gram stain from leaking out. These cells show up purple. Gram-positive bacteria have a cell wall approx 4x thicker than the plasma membrane.
- Gram-negative bacteria: the thin peptidoglycan cell wall allows most of the gram stain to be washed off. These cells show up pink. Outside of the cell wall, gram-negative bacteria have a phospholipid bilayer that is more permeable than the first (even glucose passes through). The outer membrane protects against certain antibiotics such as penicillin.
Bacterial Flagella
Made from the globular protein flagellin. NOT to be confused with eukaryotic flagella, which is composed of microtubules! It is propelled using the energy from a proton gradient rather than ATP.
Bacterial Reproduction
Do not reproduce sexually. They have three alternative forms of genetic recombination:
- Conjugation
- Transformation
- Transduction
Or binary fission (asexual).
Binary Fission
The circular DNA is replicated: two DNA polymerases begin at the same point on the circle (origin of replication) and move in opposite directions making complementary single strands that combine with their template strands to form two complete DNA double stranded circles. The cell divides making two identical daughter cells.
Conjugation
A method of genetic recombination which requires that one of the bacterium have a plasmid (small circle of DNA that exists/replicates independently of the bacterial chromosome) with the gene that codes for the sex pilus (a hollow protein tube that connects two bacteria to allow the passage of DNA). This is called the F plasmid (fertility factor, F factor).
The DNA passage is not always from the cell containing the plasmid to the cell that does not.
One end of the plasmid strand begins to separate from its complement as its replacement is replicated. The loose strand is then replicated and fed through the pilus.
R Plasmid
Donates resistance to certain antibiotics. Can also initiate conjugation.
–> prescribing multiple antibiotics for patients to take at one time promotes conjugation of different R plasmids providing different resistances to antibiotics to produce a super-bacterium that contains many antibiotic resistances on one or more R plasmids. Some R plasmids are readily transferred between species, further promoting resistance and causing serious health problems for humans.
Transformation
The process by which bacteria may incorporate DNA from their external environment into their genome; may be initiated due to external environment in the lab or lyses of other bacteria.
Ex: mix heat-killed virulent bacteria with harmless living bacteria. The living bacteria receive the genes of the heat-killed bacteria through transformation and become virulent.
Transduction
The transfer of DNA via a virus. The capsid of a bacteriophage mistakenly encapsulates a DNA fragment of the host cell. When these virions infect a new bacterium, they inject harmless bacterial DNA fragments instead of virulent viral DNA fragments. This is mediated by a virus vector. Can be mediated artificially in a lab.
Virus
Consists of a capsid protein coat that contains the nucleic acid (either DNA or RNA, never both).
Most animal viruses surround themselves with a lipid-rich envelope either borrowed from the membrane of their host cell or synthesized in the host cell cytoplasm; it typically contains some virus-specific proteins.
All organisms experience viral infections.
A viral infection begins when a virus adsorbs to a specific chemical receptor (usually a glycoprotein) site on the host. Then the nucleic acid of the virus penetrates into the cell.
Viruses are very small -> a bacterium is the size of a mitochondrion, and hundreds of viruses may fit within a bacterium.
Virion
The inert form of a virus that exists outside the host cell.
Bacteriophage
A virus that infects bacteria, injects its nucleic acid through the tail after viral enzymes (from within the capsid) have digested a hole in the cell wall.
Structure: tail, base plate, and tail fibers.
1. Viral DNA is injected into the host cell.
2. Viral DNA is transcribed and replicated.
3. The capsid is formed.
4. The host cell lyses releasing hundreds of viral progeny.
Prophage
The name of the virus when it is incorporated into the host cell’s DNA.
Lytic Infection
The virus commandeers the cell’s reproductive machinery and begins reproducing new viruses. The cell may fill with new viruses until it lyses or it may release the new viruses one at a time in a reverse endocytotic process.
Latent period: the period from infection to lysis.
Virulent virus: a virus following a lytic cycle.
Lysogenic Infection
The viral DNA is incorporated into the host genome, or, if the virus is an RNA virus and it possesses the enzyme reverse transcriptase, DNA is reverse-transcribed from RNA and then incorporated into the host cell genome.
Temperate virus: a virus in the lysogenic cycle.
Provirus: the infected cell while the viral DNA remains incorporated in the host DNA and the virus is dormant/latent (prophage if the host cell is a bacterium).
The dormant virus may become active when the host cell is under stress (like exposure to UV light and other carcinogens). When it becomes active, it becomes virulent.
(think: lysogenic is a longer word than lytic, it is also a longer cycle; lyso”gen”ic incorporates its genes.)
Classification of Viruses by Nucleic Acid
Plus-strand RNA: proteins can be directly translated from the RNA.
Ex: common cold, retroviruses (carry reverse transcriptase) like HIV
Minus-strand RNA: the complement to mRNA must be transcribed to plus-RNA before being translated.
Ex: measles, rabies, the flu
Double stranded RNA
Single and double stranded DNA
Vaccine
Either an injection of antibodies or an injection of a non-pathogenic virus with the same capsid or envelope.
Carrier Population
An animal that carries a virus without any adverse symptoms which maintains the virus’s ability to reinfect another animal population.
Fungi
Multicellular (except yeast), eukaryotic heterotrophs that spend most of their lives in the haploid state. They can reproduce sexually or asexually. May contain one or more nuclei which may or may not be identical. Lack centrioles. Mitosis takes place entirely in nucleus and the nuclear envelope never breaks down.
- exodigesters: digest their food while it is outside of their bodies and then absorb the nutrients.
- saprophytic: consume dead or decayed organic matter.
- septa: cell walls made of the polysaccharide chitin; usually perforated to allow exchange of cytoplasm between cells (allows rapid growth).
- chitin: more resistant to microbial attack than cellulose, same substance of which the exoskeleton of arthropods is made.
–> more similar to human cells than bacteria so drugs that attack fungi are more likely to affect human cells than antibiotics.
Mycelium
The tangled mass of multiple branched thread-like structures (hyphae) of fungi in their growth state.
Asexual Reproduction of Fungi
- When conditions are good! If good for the parent, will be good for asexually produced offspring that are exactly like the parent.
- > Hyphae are haploid and some may form reproductive structures that release haploid spores that give rise to new mycelia. In yeasts, asexual reproduction occurs by budding (aka cell fission) in which a smaller cell pinches off from the single parent cell.
Note: spore formation is not always via asexual reproduction.
Sexual Reproduction of Fungi
- When conditions are tough! If bad for the parent, may not be bad for sexually produced offspring that are different from the parent.
- > Occurs between hyphae from two mycelia of different mating types + and -. The two hyphae grow towards each other and form a conjugation bridge. They each produce a gamete and their nuclei fuse to produce a (dormant) diploid zygote. When activated by the appropriate environmental conditions, it undergoes meiosis to produce haploid cells, one of which immediately begins to asexually produce many spores.
Cytoplasmic Streaming
The directed flow of cytosol and organelles around large fungal and plant cells through the mediation of actin.
Endocytosis
Pathway of cell bringing substances into the cell.
-Phagocytosis: cell membrane protrudes outward to engulf the particulate matter. Only a few specialized cells do this. Need membrane protein receptors for the particulate matter.
-Pinocytosis: extracellular fluid is engulfed by small invaginations of the membrane. Performed by most cells; nonselective.
(-Receptor mediated: uses clathrin-coated vesicles, specifically brings in ligands.)
Neuronal Communication
Rapid, direct, and specific.
Hormonal Communication
Slower, spread throughout the body, affects many cells and tissues in many different ways.
Dendrites
Receive the signal to be transmitted. Connected to cell body.
Axon Hillock
Region of the neuron between the dendrite and the axon where the action potential is initiated.
