Chapter 12,13,21 Flashcards
what is cell division?
process by which a single cell becomes two daughter cells
what requirements must cell division satisfy?
daughter cells must:
1. receive complete genome set
2. be large enough to split into two
When might cell division happen?
GRR
- growth
- replacement
- reproduction
how is a genome organized in a prokaryote?
ONE circular bacterial chromosome
how is a genome organized in a eukaryote?
MULTIPLE linear chromatin
How are plasmids different from bacterial chromosomes?
- multiple plasmids can be present
- not part of bacterial chromosome
- genes in plasmids can still be read and transcripted
how do prokaryotes reproduce?
binary fission
what are some characteristics of binary fission?
it is quicker than mitosis because prokaryotes are smaller and simpler
Describe the process of binary fission
- DNA attached to cell membrane
- DNA replication occurs bidirectionally
- Daughter DNA also attached
- cell elongates, attach sites move apart
- synthesis of new cell membrane and wall
- continued synthesis, two identical cells
how many genes are in one eukaryotic cells?
~ 30,000
where are genes located in one eukaryotic cell?
nucleus, mitochondria, chloroplast
how are genes stored in a human cell? (structure)
condensed into chromatin
what are nucleosomes?
DNA + histone proteins
describe the path of condensing DNA
nucleosomes → chromatin → chromosomes
what is a karyotype?
portrait formed by the number and shapes of chromosomes representative of a species
what stage are DNA in karyotypes in?
before cell division due to absence of sister chromatids
what are benefits of an organized chromosome?
easier for transport
what are benefits of an untangled chromatin?
easier to read for transcription
what are homologous chromosomes?
two chromosomes that match by LPL
- length
- centromere position
- gene location
what are alleles?
different versions of a gene
what are autosome chromosomes?
chromosomes that do not determine sex
what characteristics must be met for cell division to proceed?
every chromosome in parent cell must be duplicated so each daughter cell receives FULL SET of chromosomes
How do sister chromatids not completely separate in DNA duplication?
centromeres hold them together, helping the sister chromatids stay side by side
what is the difference between sister chromatids and nonsister chromatids?
sister chromatids are genetically identical
nonsister chromatids are homologous but contain different alleles, not genetically identical
what are characteristics of the centromere?
- no genes in centromere region
- site for connecting to kinetochores
- where microtubules attach to for separation of chromatids
what are the stages of the cell cycle?
- Interphase
- M phase
what is interphase?
time when cell makes many preparations for division (DNA replication, cell size increase, components increase
what is G₀ phase?
“resting phase” no active prep for cell division
what is G₁ phase?
cell size and protein content increases in preparation for DNA synthesis “S” phase
- proteins needed for DNA replication are synthesized (helicase, ligase, SSBPs)
what is S phase?
chromosomes duplicated by DNA replication
what is G₂ phase?
cell prepares for mitosis and cytokinesis
- proteins required for M phase are synthesized
- nuclear envelope encloses nucleus
- two centrosomes form in animal cells
- chromatin not yet condensed
- visible nucleolus
what is M phase?
time when parent cell divides into two daughter cells, includes mitosis and cytokinesis
what is the difference between mitosis and cytokinesis?
mitosis - nucleus is split into two
cytokinesis - cell splits into two
what type of cells remain in the G₀ phase?
nondividing cells
- skeletal muscle cells
- nerve cells
what happens in prophase?
- microtubules emerge from two centrosomes, forming mitotic spindle
- centrosomes move apart towards their opposite pole
- in nucleus, chromosomes coil, compact, condense into chromosomes, sister chromatids still tgt
-nuclear envelope disappears
what are centrosomes?
microtubule-organizing centres for animal cells
what happens in prometaphase?
-nuclear envelope breaks down
-microtubules of mitotic spindle attach to chromosomes by the kinetochores
what are kinetochores?
proteins associated at centromeres (specifically for each sister chromatid), forming attachment site for a microtubule
what is the function of the asters from the centrosomes that attach to the cell membrane?
to anchor them to cell membrane, allows them to stay at their poles
what does the kinetochore complex ensure?
ensures that each sister chromatid is attached to a microtubule radiating from one of the poles of the cell
what happens in metaphase?
- chromosomes at cell equator/metaphase plate
- kinetochores of sister chromatids face opposite poles
what is a spindle?
entire structure formed by kinetochore and nonkinetochore microtubules
what happens in anaphase?
- sister chromatids separate at centromeres
- the two liberated chromosomes move to opposite poles as kinetochore microtubules shorten
- cell poles move further apart, elongating cell
- two ends of cell have equivalent and complete chromosome sets by the end
what happens in telophase?
- microtubules of mitotic spindle break down and disappear
- nuclear envelope reforms around each chromosome set, creating two new nuclei
- chromosomes decondense
what happens in cytokinesis?
parent cell’s cytoplasm and divides into two daughter cells
- in animal cells - formation of cleavage furrow forms in the middle, contracting ring of filaments pinch parent cell into two
what would happen if mitosis occurred but not cytokinesis?
parent cell has two nuclei but it remains as one cell
instead of 23 pairs, there is 46 pairs present, duplicated info
what roles does mitosis play?
produces genetically identical cells for:
- asexual REPRODUCTION
- development and GROWTH
- maintenance and REPAIR
How is meiosis different from mitosis?
- takes place in two sets of divisions, I and II
- results in FOUR HAPLOID cells
- each cell is genetically UNIQUE
how is mitosis a eukaryotic process?
- involves linear chromosomes
- involves nuclei
explain differentiated cells in terms of genotype and phenotype
differentiated cells are genotypically the same but phenotypically different, they all contain the same genes but express different genes to produce different genetic products
what is cell differentiation?
stem cells turn into specialized cells by expressing different genes
how do cells know what type they can differentiate into?
- cytoplasmic determinants (internal)
- induction (external)
what are cytoplasmic determinants?
internal molecules located in the cytoplasm that cells receive and follow one distinct developmental pathway into a distinct specialized cell
what is cell induction?
external/environmental molecules that cells receive to follow one distinct developmental pathway into a distinct specialized cell
how are transcription factors involved in cell differentiation?
transcription factors are proteins that bind to promoter regions in DNA, resulting in transcribing genes into mRNA. different types of transcription factors bind to different promoter regions, resulting in different genes being transcribed
what are external signals that generate differentiated cells?
external molecules that bind to receptors on a cell’s surface, inducing differentiation of cells into different cell types
what is induced pluripotency?
turning of differentiated cells back into stem cells (inducing them back into pluripotency)
how is induced pluripotency used in organisms?
personalized medicine, can make cells needed for normal functioning from one’s own induced pluripotent stem cells
why does somatic cell nuclear transfer (cloning) result in organisms that die young/ have a lower life expectancy?
somatic cells have shortened telomeres, so cloned organism will have significantly shorter telomeres than what a usual young organism would have
how is each daughter cell from meiosis genetically unique?
- random separation/independent assortment of homologous chromosomes during meiosis I
- crossing over during meiosis I
- fertilization of unique egg and sperm cells
how does random separation/independent assortment of homologous chromosomes result in genetic variation?
- a random mix of paternal and maternal chromosomes are present in each daughter cell
how does crossing over result in genetic variation?
- new genetic combinations made, new alleles made in each chromosome
- the points where crossing over occurs are different for each chromosome, resulting in different sets of recombinant chromosomes for each daughter cell
how does fertilization of unique egg and sperm cells result in genetic variation?
- each gamete cell contains different genetic info, and when fertilization occurs, the different genetic info combine to make a zygote with a genetically unique genotype
what happens in prophase I?
- chromosomes condense into sister chromatids
- homologous chromosomes pair up with each other side by side
- nonsister chromatids form chiasmatas and exchange DNA segments
- nuclear envelope disintegrates
- microtubules emerge from two centrosomes, forming mitotic spindle
- centrosomes move apart towards their opposite pole
what is synapsis?
pairing of homologous chromosomes
side by side
gene for gene
what is crossing over?
events where nonsister chromatids of homologous chromosomes exchange DNA at the chiasmatas, resulting in a new combination of alleles and the formation of a recombinant chromosome
no nucleotides gained or lost
what are tetrads/bivalents?
homologous pairs that underwent synapsis and joined at the chiasmatas
what happens in metaphase I?
- tetrads align at cell equator, with one chromosome facing each equator
- microtubules attach to kinetochore of one chromosome of each tetrad
how is metaphase in meiosis I different from mitosis?
there are 23 tetrads in meiosis I
there are 46 chromosomes in mitosis
what is the number of combinations for chromosomes packaged into gametes?
2^n
each gamete an organism produces contains 1 of the 2^n possible combinations of chromosomes
what happens in anaphase I?
- pairs of homologous chromosomes separate as they are pulled into opposite directions
- sister chromatids remain attached at centromere and move as one unit
what happens in telophase I?
- nuclear envelope reforms around chromosomes
- each chromosome still consists of two sister chromatids
- each cell half now has half of the diploid set of chromosomes, meaning each cell half is now haploid
- cytokinesis occurs simultaneously via cleavage furrow or cell plate formation
- two haploid daughter cells with two sister chromatid chromosomes are formed
what happens at the end of meiosis I?
- formation of cell plate or cleavage furrow
- no chromosome replication occurs as chromosomes are already duplicated and have two chromatids
what happens in prophase II?
- spindle forms
- nuclear envelope disintegrates again
- chromosomes still composed of two chromatids start moving towards metaphase plate
what happens in metaphase II?
- sister chromatids are arranged at metaphase plate
- the two sister chromatids are no longer genetically identical due to crossing over in prophase I
what happens in anaphase II?
- sister chromatids separate
- the sister chromatids of each chromosome now moves as two newly individual chromosomes towards opposite poles
what happens in telophase II?
- chromosomes arrive at opposite poles
- nuclei reform
- chromosomes begin decondensing
- cytokinesis separates cytoplasm, resulting in four total haploid daughter cells
- each daughter cell is genetically distinct from other daughter cells and parent cell
how does cytoplasmic division occur in males?
- cytoplasm is divided equally into the four daughter cells
- cytoplasm is mostly eliminated during sperm development
- what remains is nucleus containing DNA and a flagellum
how does cytoplasmic division occur in females?
- one oocyte and three polar bodies are made
- oocyte retains most of cytoplasm from parental cell, can develop into an egg
- the three other polar bodies receive only small amt of cytoplasm as they eventually disintegrate
why can’t cell division occur all the time?
uncontrolled cell division leads to cancer
how is the progression of the cell cycle controlled?
cyclin proteins regulate cyclin-dependent kinase activities
if present, cyclins bind to CDKs and activate enzyme, promoting cell division
how do cyclin-dependent kinases promote cell division?
cyclin dependent kinases activate target proteins (transcription factors, enzymes) that catalyze pathways leading to cell division by phosphorylating them
what does the G1/S cyclin-CDK complex do?
during end of G1/start of S phase, the complex prepares cell for DNA replication by phosphorylating transcription factors that lead to synthesis of proteins needed for DNA replication in S phase
what does the M cyclin-CDK complex do?
complex helps prepare cell for mitosis around end of interphase by phosphorylating transcription factors that lead to synthesis of proteins for nuclear envelope breakdown and chromosome condensation
what are the three major checkpoints that cells have during the cell cycle?
- at end of G1 - checks for damaged DNA
- at end of G2 - checks for presence of unreplicated DNA
- at M, before anaphase - checks for attachment of all chromosomes to the spindle before cell progresses with mitosis
what are the three possibilities for a cell during its lifecycle?
- remain non-dividing but sitll alive and functioning (G₀ phase)
- grow and divide
- die
how many times can a cell divide before dying?
50-70 times
what is apoptosis?
programmed cell death to prevent uncontrolled growth and rapid formation of mutations
- suicide enzymes produced in cell and kills cell
- cell dismantles itself in an orderly fashion
what is the difference between a cell that underwent apoptosis and a cell that died in other ways?
- apoptosed cells die in an orderly fashion and its components can be recycled
- cells that died in other ways show signs of inflammation, reactions from body
what are the three characteristics of cancer cells?
- don’t apoptose if given constant nutrient supply
- divide rapidly and continually
- not inhibited by contact with other cells, building up on top of one another, forming lumps and tumours
how do cancer cells form?
normal genes that participate in cell division and other processes are mutated via X-rays, radiation, etc.
