Chap 17: Cell Division Flashcards
What is interphase?
it occurs between cell divisions. normal cell prepares for the mitotic phase. 90% of the cell cycle. unable to see chromosome
What is the G1 phase?
growth before division.
What is the S phase?
synthesis (S phase) replication of DNA.
What is the G2 phase?
prepares for cell division.
What do mitotic divisions consist of?
it consists of prophase, metaphase, anaphase, and telophase.
Why do cells divide?
to repair, grow and replace cells
What is a chromosome?
made of nucleic acids (DNA) and proteins.
What is an uncondensed chromosome?
long, thin strands that cannot be seen under a light microscope (interphase)
What is a condensed chromosome?
can be seen under a light microscope (prophase)
What is a chromatid?
1 of two copies of a replicated chromosome. joined together in the center by a chromosome
What is binary fission?
asexual reproduction. “mother” cell divides into 2 identical “daughter” cells. occurs in bacteria (prokaryotes)
What happens during mitosis?
double-stranded chromosomes become single-stranded. each daughter cell gets one of the single-stranded pairs. the cell uses single strands of DNA to build a complementary strand.
What is the purpose of mitosis?
to replace worn-out cells with new ones, production of body cells and tissue growth.
How do cells prepare themselves for mitosis?
new cell membranes, producing enzymes for chemical reactions and control duplication of DNA
What is chromatin?
combination of DNA and proteins. the form of chromosomes found during interphase
What happens during prophase?
chromosomes form from threadlike chromatin and they condense.
2 identical chromatids are joined at the centromere. centrioles move to opposite sides of the nucleus and provide attachment for spindle fibres.
nuclear membrane and nucleolus disintegrate
What happens during metaphase?
chromosomes with two chromatids (sister chromatids) line up at the equator.
spindle fibres attach to the centromere.
most visible stage
spindle apparatus
spindle fibers + centrioles
What happens during anaphase?
centromeres split and spindle fibres shorten one chromatid from each pair moves to opposite poles; now is called a chromosome
if chromatids do not separate and both move to the same pole of the diving cell, this is called:
nondisjunction
What happens during telophase?
spindle fibres disappear
chromosomes unwind/uncoil
two new nuclei form around each set of genetic material
cytoplasm begins to divide by forming a cleavage furrow at the equator. 2 daughter cells separate.
cytokinesis
why do cells stop dividing?
senescence and cell specialization
What is senescence?
process of aging
the more specialized a cell
the less able it is to undergo mitosis
what 2 cell types in a human body escape aging?
sperm-producing cells, and cancer cells
What is cancer?
uncontrolled cell growth and division.
What are identical twins?
originate from a single cell
during mitosis (after fertilization) one of the cells breaks free and a 2nd embryo develops
same gender, blood type and similar facial structures
What are fraternal twins?
originate from 2 different eggs and are fertilized by different sperm cells
don’t have the same genes
What is cloning?
production of genetically identical organisms derived from a single individual by asexual means
How does plant cloning technology work?
can be done through grafting, cuttings, and runners.
have predictable characteristics
undergoes mitosis to increase in size, and specializes to form roots, stems or leaves
What are the 6 steps to clone a frog?
- nuclear transplant, extracts the nucleus from an unfertilized egg cell (n)
- cell is enucleated
- insert a nucleus from a cell of another frog (2n)
- egg cell with a transplanted nucleus divides normally and grows into an adult frog
- an adult is a clone of the frog that donated the nucleus
What is a somatic cell?
all body cells except sex cells, diploid cells (2n)
What does totipotent mean?
describes a cell that is able to bring a cell to turn into any type of cell (STEM cells)
What is a telomere?
caps at the ends of chromosomes. reduce in length each time a cell goes through a cell cycle and divides
What is telomerase?
an enzyme that affects the length of the telomere. not present in most normal cells.
what is the goal of meiosis?
cell reduction
what are the benefits of sexual reproduction?
- genetic variation
- 2 sets of chromosomes, can act as back-up
- repair mechanisms
what are the disadvantages of sexual reproduction?
- costly/lots of energy
- infection possibility
- only passes on half of our genes to offspring
ova (eggs), sperm cells. are the only cells in the body NOT produced by mitosis.
gametes
where does meiosis occur?
in germ cells of gonads (reproductive organs)
46 chromosome number is
diploid (2n)
23 chromosome number is
haploid (n)
paired chromosomes are:
homologous chromosome
meiosis
2 cell divisions produce
4 haploid cells
What happens in prophase 1 (5 points)
- chromosomes form homologous pairs which form tetrads (2 pairs of joined chromatids)
- joining of these chromosomes is called synopsis
- crossing over (exchange of genetic material) occurs and genetic info is switched; genes aren’t lost - they are recombined with genes from the other chromatids
- nuclear membrane disappears
- centrioles move apart
What happens in metaphase 1?
- homologous chromosomes (tetrads) attach themselves to spindle fibres and line up along the equatorial plate. (HINT: if u see double dating, its meiosis)
What happens in anaphase 1? (4 points)
- homologous chromosomes move toward opposite poles.
- segregation - reduction division occurs. joined chromatid pairs of each tetrad pulled to opposite poles
- chromatids do NOT separate yet
- each chromosome remains double stranded
What happens in telophase 1? (4 points)
- chromosomes form chromatin by unwinding/uncoiling
- nuclear membranes reappear
- cytokinesis begins
- 2 daughter cells with a haploid number
What happens in meiosis 2?
occurs at approximately the same time in each haploid daughter cell. NO S phase, NO duplication of DNA
What happens in prophase 2? (3 points)
- nuclear membrane dissolves
- spindle fibres begin to form
- chromosomes appear
What happens in metaphase 2? (2 points)
- arrangement of chromosomes, each with 2 chromatids, along an equatorial plate (Single File)
- chromatids remain pinned together by a centromere
What happens in anaphase 2? (2 points)
- the movement of sister chromatids to opposite poles
- nuclear membrane begins to form around chromosomes
What happens in telophase 2?
- 2nd division of cytoplasm is completed
- nuclear membranes reform
- four haploid daughter cells are produced
are gametes haploid or diploid?
haploid
What happens in spermatogenesis? (2 points)
- production of sperm which occurs in the seminiferous tubules of the male testes
- sperm cells receive equal amounts of cytoplasm
What happens in oogenesis?
- production of an egg by the female which occurs in the ovaries
- one cell (out of the 4 produced) receives most of the cytoplasm while the smaller ones form polar bodies that degenerate
