Quiz #7 Flashcards
What are two inhibitors of cellular respiration?
cyanide
dinitrophenol
How does cyanide inhibit cellular respiration?
cyanide ions act as an irreversible enzyme inhibitor binding to the iron atoms of cytostome c oxidase complex (Complex IV)
no electron transport
no H+ pumping
no ATP synthesis
note that all electron flow through the chain will stop if Complex IV is inhibited
How does dinitrophenol inhibit cellular respiration?
makes mitochondria inner membrane permeable to H+
therefore no H+ gradient forms (in extreme case)
no flow back through ATP synthase
no ATP made
electron transport chain continues
energy dissipates as heat
DNP “uncouples” electrons transport
and formation of the H+ gradient, called an uncoupler
Why are alternative metabolic processes used?
although essential for many organisms, oxygen is very toxic
cellular respiration generates a lot of ATP from glucose, but if oxygen is unavailable for cellular respiration, an organism that uses an electron transport chain has two options: Die or use a secondary metabolic pathway
What are two ways to make ATP from organic molecules without oxygen?
Continue to use electrons transport chain, but use a different terminal electron acceptor, some prokaryotes that live in anaerobic conditions can perform anaerobic respiration
Use glycolysis to make ATP (recall this part of pathway does not require oxygen). The oxidizing agent is NAD+ but without the electron transport chain, NADH will quickly build up. To continue using glycolysis, NAD+ must be regenerated
What is alcohol fermentation?
pyruvate is converted to ethanol in two steps, with release of CO2
alcohol fermentation by yeast is used in brewing, winemaking, and baking
What is lactic acid fermentation?
pyruvate is reduced by NADH, forming lactate as an end product, without release of CO2
lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt
human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce
How are nerve cells in the brain affected by low levels of oxygen?
these are the first to die if deprived of oxygen
cannot make ATP unless O2 is present
cannot maintain proper ion balance and membrane potential
leads to cell damage, cessation of nerve function, death to organism
How is glycolysis regulated?
phosphofructokinase (PFK) is the key enzyme in the control of glycolysis
PFK activity is inhibited allosterically by high levels of ATP in cells
AMP (adenosine monophosphate) stimulates PFK to be more active, when ATP is used by reactions in the cell, there are various possible products
Citrate, the first product in the Krebs Cycle, inhibits PFK, citrate formation is fed by glycolysis
What is cell division and growth in eukaryotes and prokaryotes?
cell division by binary fission or mitosis produces two genetically identical cells
the process of cell division and segregation of chromosomes to daughter cells is more complicated in eukaryotes than prokaryotes
this is partly due to the fact that eukaryotes have much more DNA and multiple chromosomes
What processes are involved in cell division?
A reproductive signal “tells” the cell to divide, may originate from either inside or outside the cell
DNA replication, each daughter cell receives an identical copy of the complete instructions to perform all cellular functions
DNA segregation, the replicated DNA gets distributed to the new cells
Cytokinesis, the cytoplasm (or cytosol) divides to form two new cells each with its own cell membrane (a cell wall, if parent had one)
What is generation time?
time required for cells to divide
is determined by type of organism, level of nutrients, temperature
What does the graph of dividing cell populations look like?
slope constantly increases because of exponential growth
log plot gives straight line (easier to compare)
these graphs represent an ideal, theoretical situation, that assumes unlimited nutrients and no waste build up
What are the stages of cell growth?
Lag Phase
Log Phase
Stationary Phase
Death Phase
What is the lag phase in cell growth?
can last minutes to days
depends on species and physiological history of the starting cells
little to no cell division occurs
but cells may have a lot of metabolic activity (growing in volume, synthesizing enzymes, proteins, RNA, etc.)
What is the log phase in cell growth?
cells begin to divide
cell number doubles at a rate characteristic of the organism
growing population uses up nutrients, excretes waste product
What is the stationary phase of cell growth?
growing population uses up nutrients, excretes waste products
because of this, metabolic rate of cells decreases
cells die at a rate approximately equal to the rate of cell division
What is the death phase of cell growth?
more cells die than divide
causes aren’t always clear
cells lysis due to damaged cell walls
toxicity from waste products
What is DNA Replication in prokaryotes?
two regions of the DNA molecule play important roles in its replication
ori (origin): the site on DNA molecule where its replication is initiated
ter (terminus): the site where replication ends
prokaryotic DNA synthesis occurs at the same time as other metabolic processes in the life cycle, this is different from eukaryotes, which separate DNA replication from other stages of life
What is DNA segregation in prokaryotes?
start separating DNA as soon as they can
FtsZ protein distantly related to eukaryotic tubulin, before DNA replication, FtsZ is distributed throughout the cytosol
immediately after DNA starts to replicate, other dynamics proteins bind to a region next to the ori and form filaments that help separate the two replicating nucleoids as they finish replication
then, FtsZ proteins start to congregate between the separating nucleoids
What is cytokinesis in prokaryotes?
FtsZ proteins form a ring that “pinches” the cell membrane inwards until it separates the cytosol
as the membrane pinches in, new cell wall materials are deposited in the plane of the FtsZ ring (new barrier is termed a septum), which finally separates the two cells
What is eukaryotic cell division?
mitosis and cytokinesis
they first divide the nucleus (mitosis) and then the cytoplasm (cytokinesis)
What is eukaryotic reproductive signals?
unlike prokaryotes, most eukaryote cells do not simply divide whenever conditions are favorable, cells within a multicellular organism may not divide for many days, months, or years
the signals that control cell division are often related to the function of the whole organism, rather than the individual cell
What is eukaryotic DNA replication?
eukaryotes have more than one chromosome, but each one replicates in a manner similar to prokaryotes, replication of DNA occurs at a specific stage of the cell cycle
replication initiates at specific sites in DNA (origins), most eukaryotic chromosomes have multiple origins of replication because they are very long
What is eukaryotic DNA segregation?
more complicated than prokaryotes
there is a nuclear envelope
there are multiple chromosomes
each chromosome can be very long
replicated DNA molecules become highly condensed (packaged) in the nucleus before they segregate
completely replicated DNA molecules are initially connected to each other (as sister chromatids)
What is a centromere?
a physical constriction of the duplicated chromosome, the sister chromatids are most closely attached at this site (we will discuss the function of the centromere later)
What is eukaryotic cytokinesis?
refers to the division of the cytoplasm
the final stage of cell reproduction
mechanism different in animal vs. plant cells
What are the steps involved in meiosis?
pairing of replicated homologues
recombination
segregation of homologues (division, completion of meiosis I)
segregation of sister chromatids (division, completion of meiosis II)
What is interphase?
chromosomes are present (long, thin fibers of chromatin (DNA + proteins)), but not visible under a microscope as distinct entities
metabolic activity and growth occur throughout interphase, but the phases allow control over decisions to grow, change shape/behavior, replicate DNA, or divide
What is G1 phase?
each chromosome is long and thread-like, a double-stranded helix of DNA plus associated proteins
each chromosome has centromere: specialized DNA sequence important for chromosome segregation
G1 prepares the cell for DNA replication
What happens at the start of S phase?
the two strands of the helix unwind (unwinding starts at an origin)
each serves as a template for synthesis of a new strand
What happens at the end of S phase?
one chromosome with 2 sister chromatids
the DNA in each chromatid consists of one “old strand” and one “new strand”
What is G2 of interphase?
DNA replication is finished, now the cell prepares for chromosome segregation and cell division
when centrioles duplicate, the new one (called the daughter centriole) grows out from the older centriole (called the mother centriole)
two centrosomes (duplicated in S phase) usually stay close together, each centrosome has a pair of centrioles
What is prophase?
the two centrosomes begin to separate because of microtubule growth and motor proteins pushing against opposing microtubule
nucleoli disappear
chromatin fibers become more condensed and visible
What is prometaphase?
nuclear envelope starts to break down, (e.g. lamins disassemble, and membrane forms small vesicles that remain around the chromosomes)
this allows microtubules to grow into the area and make contact with kinetochores
if a microtubule plus end “hits” a kinetochore that microtubule becomes “captured”
What is kinetochore?
a large structure made of ~100 different proteins, that assembles on the DNA (at the centromere), each chromatid has one kinetochore, the pair face in the opposite directions
captures microtubules and is required for proper chromosomes congression and separation of sister chromatids
What is metaphase?
chromosomes congress to the “equatorial region”, forming a metaphase plate
What is anaphase?
the shortest stage of mitosis
begins when cohesion proteins are cleaved
tension builds up initially due to kinetochore microtubules pulling equally in opposite directions
tension released, and chromatids more rapidly apart, with kinetochore leading the way
What are the two different ways that mitotic chromatid segregation can occur?
shortening the distance between poles and chromatids (anaphase A)
movement of spindles poles (centrosomes) apart (anaphase B), depending on the cell involved, it may use either method or both
What is telophase?
two daughter nuclei form in the cell
nuclear envelope starts to reform
chromosomes start to de-condense (become less visible)
division of the nucleus into two genetically identical nuclei is complete
What is cytokinesis?
refers to the splitting of the cytoplasm in a eukaryote
it begins during late anaphase and continues through telophase until complete separation of daughter cells into distinct compartments
an actin-based contractile ring forms at the membrane
Why would a cell ever divide asymmetrically?
to create two daughter cells that are not identical to each other (different in size, components, etc.)
