Chapter 10 - Cell Reproduction Flashcards
Sexually reproducing organisms start life as a single cell called…
A zygote
Non sexual cells reproduce through what?
Cell division
The result of division of a single parent cell to the production of two genetically identical what cells?
Daughter cells
All of a cells DNA is called it’s….
Genome
The genome of prokaryotes have what characteristics? Where are they found in a prokaryotic cell?
They are double stranded DNA molecules in the form of a loop, and found in an area called the nucleoid region
Some prokaryotes have small loops of DNA called…
Plasmids
Eukaryotic genomes consist of what shape? What are they called?
Linear pieces of DNA called chromosomes
Sex cells are also called
Gametes
What is the difference in Number of chromosomes from gametes to somatic cells? For example human cells
Gametes have half the number of chromosomes of somatic cells, for example human gametes have 23, somatic has 46
Body cells contain 2 matched or homologous sets of chromosomes while sex cells have just one set of chromosomes, what are these 2 denoted as in genetics?
Body cells containing 2 matched or homologous sets of chromosomes are denoted as diploid (2n), while human cells with just one set of chromosomes are haploid (n)
Upon fertilization each gamete contributes one set of chromosomes in a diploid cell which has matched pairs of chromosomes called…
Homologous chromosomes
Homologous chromosomes are the same length and have the same genes in exactly the same location called…
The locus
What are the functional units of chromosomes and determine specific characteristics by coding for specific proteins?
Genes
What are the possible variants of the specific characteristics coded by genes?
Traits
A complete gene is made up of how many alleles?
2 (1 from each parent)
Alleles can be identical or not, what are they called in each case?
Identical (homozygous), different (heterozygous)
What are the only homologous pair of the 23 chromosomes to have genes for different characteristics at the same locus?
The X and Y chromosomes
What is at the first level of compaction in chromosomes?
The DNA double helix is wrapped around a core of 8 histone proteins along the entire length of the chromosome now called chromatin,
The bead like DNA/histone complexes are called what? How much larger would they be without histones?
They are called nucleosomes, they would be 7 times larger without histones
What is the second level of compaction in chromosomes?
The nucleosomes and the linker DNA coil into 30nm fibers, shortening the chromosomes by about 50x
What is level 3 of compaction in chromosomes? What is the purpose of this level?
A variety of fibrous proteins further condense the chromatin in a non dividing cell, this makes sure no DNA overlaps
If a cell is to divide it enters what phase of interphase?
The S-phase where replication of the entire chromosome occurs
Replicated sister chromatids bind together with cohesion proteins, the closest point being where?
The centromere
What are the 2 major phases of the cell cycle?
Interphase, and the mitotic phase
If cytokinesis does not occur when it needs to what happens?
Multiple nuclei is produced
Overall what happens in interphase? What three stages of interphase is there?
The cell undergoes growth processes while preparing for cell division. The 3 stages include G1, S, and G2
What happens in G1 phase of interphase?
Called the first gap it is where little change is visible in microscope, but much occurs biochemically like chromosomal structure is completed, cell reaches its full size, energy reserves are accumulated and DNA is in its chromatin state
What happens in the S phase of Interphase?
DNA synthesis happens here it produces two identical chromatids from each DNA strand, the centrosome is duplicated which will give rise to the mitotic spindle which will move the chromatids and help organize cell division
What happens in the G2 phase of interphase?
Now in the second gap, energy stores are replenished, proteins necessary for chromosome manipulation and movement are duplicated, the cytoskeleton is dismantled to provide resources for the mitotic phase
Briefly what does the mitotic phase do? What 2 main phases are there?
The duplicates chromosomes (chromatids) are aligned, seperated, and moved into new, identical daughter cells
-2 main phases are karyokinesis and Cytokinesis
What are all the stages in order of karyokinesis?
Prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis
What happens in the prophase? Be specific
-nuclear envelope starts to dissociate and membranous organelles fragment and disperse towards the periphery of the cell
-centrosomes move to opposite poles
-microtubules start to form the mitotic spindle between the centrosomes
-sister chromatids coil more tightly coiled with the help of condensing proteins and become visible in a light microscope
What happens in the prometaphase? Be specific
-each sister chromatid develops a protein structure called a kinetochore at the centromeres region, the kinetochore proteins attach and bind to the mitotic spindles
-centrosome proteins extend and attach to the kinetochores
-sister chromatids are arranged so as to face opposite poles of the cell
-polar microtubules reach only halfway and contribute to cell elongation
-astral microtubules extend only short distances from the centrosomes and aid in spindle orientation and mitosis regulation
What happens in the metaphase? Be specific
-all the chromosomes (chromatids) are aligned on a plane called the metaphase plate
-sister chromatids are tightly attached to each other by cohesion proteins and are maximally condensed
What happens in the anaphase? Be specific
-cohesion proteins degrade
-sister chromatids seperate at their centromere
-each chromatid is now called a single chromosome and are quickly pulled towards the centrosomes by the microtubules
-cell becomes elongated
What happens in telophase? Be specific
-chromosomes reach their opposite poles and begins to decondense to take the form of chromatin
-the mitotic spindle depolarizes into tubulin monomers
-the nuclear envelope forms around the chromosomes
What happens in cytokinesis?
It is the seperatiom of the cytoplasmic components into the daughter cells
-remember when it does not occur cells become multinucleated
When does animal cytokinesis start? And what happens?
In late anaphase,
a contractile ring forms just inside the plasma membrane at the former site of the metaphase plate where actin filaments form and pull the equators of the cell inward forming a fissure called a cleavage furrow which deepens as the actin ring contracts eventually cleaving the cell into 2
What happens in plant cytokinesis?
A new cell wall must form between the daughter cells during telophase, Golgi vesicles are transported on microtubules to form a phragmoplast at the metaphase plate, the vesicles fuse and coalesce from the center towards the exiting cell walls, this structure is called a cell plate and enlarged until it fuses with the cell walls, glucose then is used by enzymes to build the new cell wall between the membranes of the cell plate
What do cells do in there G0 phase?
Nothing, they are not actively preparing to divide and are inactive
(Some cells are temporarily here due to environmental factors or lack of GF)
(Some cells are even permanently in G0)
What are all the cell cycle lengths in human cells? And most typical examples?
It can be a few hours in embryonic development, 2-5 days seen in epithelial cells, or an entire lifetime spent in G0 seen in cortical neurons and cardiac muscle fibers
Fruit fly cell cycles complete in how much time? What is it due to?
About 8 minutes due to the formation of multinucleated zygotes
List some ways the cell cycle can be inhibited or initiated
-death of nearby cells can either initiate or inhibit cell division
-crowding can inhibit it
-when cells are too large their surface to volume ratio becomes too small initiating cell division
-growth promoting hormones (ex. HGH in high amounts triggers a lot of cell division resulting in gigantism, in low amounts it results in dwarfism)
What are the three main internal checkpoints that prevent a compromised cell from continuing to divide?
They are called cell cycle checkpoints and the 3 are
1) G1 checkpoint
2) G2 checkpoint
3) M checkpoint
What does the G1 checkpoint asses?
-If all conditions necessary for cell division are favorable, (the cell is irreversibly committed to division past this checkpoint)
-growth factors play an important role in carrying the cell past this checkpoint, also both internal factors like adequate reserves and cel size
-DNA damage is assessed
(if all conditions are met the cell can proceed past this checkpoint)
If conditions are not met at the G1 checkpoint what happens?
Problems may be remedied or the cell may pass into G0 and wait for conditions to improve
What is assessed in the G2 checkpoint?
-cell size and protein reserves
-all the chromosomes must be replicated, and the DNA must not be damaged (if damaged, DNA repair mechanisms may be attempted)
What is added in the M checkpoint?
When does this checkpoint occur
This occurs at the end of metaphase
-sister chromatids must be correctly attached to the spindle, since anaphase is an irreversible step the cycle will not proceed formally until the kinetochores of each pair of sister chromatids are attached to at least 2 spindle fibers arising from opposite poles
Often called the spindle checkpoint
What are the 2 types of regulator molecules of the cell cycle?
Positive or negative regulators
In brief terms what are cyclins and cyclin-dependent kinases (Cdk)?
They are positive regulators of the cell cycle, they control the progress of the cell through the checkpoints
What are the 4 types of cyclins?
Cyclin D, E, A, and B
What happens to the cyclins when the cel moves onto the next phase?
They are degraded by cytoplasmic enzymes
Where and when does each Cyclin progress the cell cycle?
-Cyclin D and E move the cell last G1 and into the S phase,
-Cyclin A moves the cell past the G2 checkpoint
-Cyclin B moved the cell past the M phase
What must happen in order for cyclins to function?
They must be bonded to a Cyclin dependent kinase and this complex must be phosphorylated, the phosphorylated Cdk/cyclin complex in turn phosphorylates the specific proteins that move the cell through the checkpoint. The cell MUST have the full suite Cdks and Cdk/cyclin complexes to proceed through the checkpoints
What are the 3 well understood negative regulators of the cell cycle? (These stop the cell cycle)
Retinoblastoma protein (Rb), p53, and p21
What are retinoblastoma proteins?
They are tumor-suppressor proteins
Where were the 3 negative regulators discovered and at what point in the cell cycle do they primarily function at?
They were discovered in cancerous cells and function primarily at the G1 checkpoint
What is and How does p53 function?
-is a multi-functional protein that acts when there is DNA damage to cells preparing for passage into the G1 checkpoint
-p53 halts the cell cycle if DNA damage is detected and recruits other proteins to repair the damage
If damage cannot be repaired by p53 what happens?
It directs cell apoptosis (cell suicide)
What does p21 do?
It enforces the halt in the cycle directed by p53 by binding to and inhibiting the action of the Cdk/Cyclin complexes
Cells under stress accumulate more levels of what inhibitor molecules?
P53, and p21
Retinoblastoma protein monitors what?
Cell size and other regulator proteins
When is retinoblastoma protein referred to as active? What does it do?
When it is unphosphorylated and binds to transcription factors like E2F blocking them from producing the proteins necessary for G1/S transition
When is retinoblastoma protein considered inactive?
When the cell size increases retinoblastoma protein is slowly phosphorylated until it releases E2F, then it is considered in an inactive state
Once E2F is released from retinoblastoma protein what can it do?
It can now turn on genes that produces the transition proteins
What must happen to both positive and negative regulators at the end of each checkpoint?
All positive regulators must be turned on and negative to be turned off
Cancer does occur despite the redundancy of the cell cycle, it is extremely critical when associated with what phase?
In the S phase during replication
Replication errors are called…
Mutations
When mistakes go uncorrected in the cell cycle what often happens?
The cell cycle speeds up as the control and repair mechanisms decrease
When uncontrolled growth outpaces normal growth in an area what can result?
A tumor
Genes that code for positive cell cycle regulators are called what? What are they called when they become mutated and cancerous?
Proto-oncogenes, when mutated they are called oncogenes
Cdk genes are considered oncogenes, so if they are not paired with their proper cyclin what might happen to the cell?
It could push through its cell cycle and sighted cells may have increased activity of positive regulators accumulating even more mutations
What do tumor suppressor genes do?
Code for negative regulator proteins that when activated can prevent the cel from undergoing uncontrolled division
What are the best understood tumor suppressor genes? What do they do to help with the uncontrolled division in a cell cycle?
Retinoblastoma proteins, p53, p21 which function by putting up a roadblock to cell cycle progression until certain events are completed
A cell with a faulty p53 gene may fail to do what? If this happens what would the process be like? (Be as detailed as you can)
Detect errors present in genomic DNA. The faulty p53 gene would not be able to signal for necessary DNA repair enzymes to be made, this DNA going uncorrected would prevent apoptosis from being triggered and the cell would become cancerous. The loss of p53 function may also prevent p21 production resulting in the loss of effective blocks on Cdk activation and the cell would proceed directly from G1 to S phase
-the daughter cells will carry this mutated p53 gene and further mutations could accumulate resulting in more tumor growth
How do bacteria divide?
Via binary fission
What is different about binary fission overall from eukaryotic cell division?
It is a much faster and easier process, there are also no histone proteins present in bacteria, however there are cohesion and condensing proteins involved
What is the whole process of binary fission? (Be specific)
The bacterial chromosome is attached to the plasma membrane at about the midpoint of the cell
-replication of the DNA is bidirectional moving away from the origin on both strands simultaneously, each new strand is pulled, seperated as the cell elongates
-after chromosomes have cleared the midpoint of the cell the cytoplasm begins to seperate, and a protein called filament temperature-sensitive mutant Z (FtsZ) directs the formation of the partition between the nucleoids
-formation of the FtsZ ring triggers the accumulation of other proteins that work to build the new plasma membrane and cell wall
-a septum is formed between the daughter nucleoids, and gradually extends from the periphery to the center of the cell, once the new cell walls are formed and in place the daughter cells seperate
What is a variant of the sequence of nucleotides at a particular location, or locus, on a DNA molecule
Alleles
