ch 17 Flashcards
what are the two types of cell reproduction
-mitosis: generates new diploid cells
- meiosis: generates haploid gametes
what is a diploid
cell has two sets of chromosomes, one from the mother and one from the father
what is a haploid
cell with only one set of chromosomes
what is mitosis
division of a parent cell into two identical daughter cells that are genetical identical to the parent cell
-nuclear division (mitosis) followed by cytoplasmic division (cytokinesis)
what is the sequence of phases for mitosis
- prophase
- metaphase
- anaphase
- telophase
what occurs during prophase
-mitotic spindle formed
- centrioles migrate to cell poles
- chromatin condenses into chromosomes
- nuclear membrane dissolves
- metabolic activity decreases
what happens during metaphase
- duplicated chromosomes (each with two sister chromatids) form single line at the equator between centriole poles
what happens during anaphase
-duplicate chromosomes (sister chromatids) separate
- daughter chromosomes are pulled toward poles by microtubules
what happens during telophase
-reverse of prophase
- mitotic spindle disintegrates
- nuclear membrane reforms
- chromosomes uncoil and revert to chromatin
what happens during cytokinesis (cytoplasmic division)
-contractile ring of filaments forms at midsection of cell and tightens, forming a cleavage furrow
- this stage overlaps telophase of mitosis
-two daughter cells formed as the contractile ring pinches them apart`
- results in two identical daughter cells (diploid)
what cells in the body divide by mitosis
all except the cells that form sperm and egg
body cells except for sperm and egg have how many chromosomes
46 chromosomes (are diploid)
- 23 pairs of them
- the chromosomes in each pair are called homologous chromosomes
in the 23 pairs of chromosomes what are the types
- 22 pairs are autosomes (not sex chromosomes)
- 1 pair of sex chromosomes
(XX female, XY male)
what is the purpose of meiosis
produce gametes(are haploid).
sexual reproduction
how many chromosomes are in meiosis
- one set of 23 chromosomes
- reduction in chromosome number from diploid to haploid is accomplished by meiosis, a special cell division process that occurs in ovaries and testes
similarities in mitosis and meiosis
-produce new cells
- similar basic steps
- start with a single parent cell
summary of mitosis
-4 stages total (plus interphase)
- somatic cells
- purpose is cell proliferation
- produces 2 diploid daughter cells
- chromosome number remians the same
- genetic variation doesn’t exist
summary of meiosis
-8 stages in total (plus interphase)
- happens in germ cells
- purpose is sexual reproduction
- produces 4 haploid daughter cells
- chromosome number is halved in each daughter cell
- genetic variation increased
Where does meiosis occur and what does it produce
in precursor cells that will produce gametes
what is the precursor cell engaged in
the cell cycle and proceeds through S
what step ensures that siblings look alike but are not clones
-theres an intermediary step that creates genetic variation in the sperm and eggs (rather than just go to mitosis and cytokinesis)
when are karyotypes determined
in metaphase when condensed chromosomes are visible
meiosis includes how many successive cell division processes and what are they
2
meiosis I: prophase I, metaphase I, anaphase I, telophase I and cytokinesis
meiosis II: prophase II, metaphase II, anaphase II, telophase II and cytokinesis
what is reduction division
in meiosis when the number of chromosomes is reduced by half…the daughter cells are haploid (n)
what does fertilization do
(haploid sperm + haploid egg) restores the diploid number of chromosomes
stages of meiosis I
Prophase I: duplicated homologous chromosomes pair up and swap segments (crossing over)
Metaphase I: homologous pairs of chromosomes line up. Double line of chromosome pairs.
Anaphase I: pairs of chromosomes separated but duplicated chromosomes stay intact
Telophase I and cytokinesis
End of meiosis I: two haploid daughter cells, but chromosomes are still in duplicated state
what is recombination
-crossing over
- creates genetic variation in our species and drives our ability to adapt during evolution
- essential for sexual reproduction
what happens in meiosis II
-each of the two daughter cells from meiosis I goes through meiosis II
- similar to mitosis
-prophase II
- metaphase II
- anaphase II - duplicated chromosomes (chromatids) separate
- telophase II and cytokinesis -nuclei have the haploid chromosome number
end of meiosis II: 4 non-identical haploid daughter cells
sex differences in meiosis
males:
- 4 sperm
- all viable, functional
female:
- unequal cytokinesis during meiosis I and II
- one egg and 3 polar bodies produced from each cell entering meiosis
- only the egg is viable
how is cell reproduction regulated
-internal surveillance and control mechanism
- several key checkpoints where “go ahead” signals must be received in order for the cycle to progress to the next phase - G1, G2, M checkpoints
what are the outside influences that effect how cell reproduction is regulated
-can modify cell cycle
- hormones
-growth factors
- presence of other cells
which types of cells divide constantly and rapidly throughout life
-skin cells -outermost layer is constantly sloughed off
- most epithelial cells- bc they line inner surfaces they are exposed to frequent damage and must be replaced
- bone marrow cells-stem cells produce red blood cells and white blood cells (these must be increased as part of the immune response)
- spermatogonia (after puberty)-the rate declines with age
which types of cells will divide under certain circumstances
-liver cells-don’t normally divide but will if part of the liver is removed
- epithelial cells surrounding the egg-granulosa cells…they begin to divide as the follicle matures
which types of cells do not normally divide in adulthood
-nerve cells
- osteocytes-trapped in the hard crystalline matrix of bone
- muscle cells-do not divide in adulthood or divide very slowly
what is differentiation
process by which a cell becomes different from its parent or sister cell
- based on different gene expression
where does differentiation begin?
after 8 cell stage-the cells are exposed to different environments inside versus outside the ball
what happens to the zygote after fertilization of egg by sperm
-zygote begins several cell divisions during which cells divide (up to 16 or 32 cells) but don’t grow and form a ball
how can cloning occur
- can occur by embryo splitting at 8-cell stage bc cells are not yet differentiated
- 16-cell stage and beyond, embryo splitting no longer works
what are the 2 factors of differentiation later in development
-developmental history of earlier cells
- local environment
more differentiation later in development
- genes are “turned on” or “turned off” at various stages of development
-vulnerability to genetic damage is influenced by the stage of development
examples of vulnerability to genetic damage is influenced by the stage of development
- genetic damage early in development = embryo or fetus may not survive
- damage later in fetal development= maybe physical deformities
- mutation in adult = dangerous or no effect
examples of external substances that are harmful to fetuses
*cigarette smoke - retards growth
*alcohol - fetal alcohol syndrome
*medications (prescription/over-the-counter) - pass through placenta
*illegal drugs: child born addicted
* environmental chemicals: in air, water, soil
* radiation- radon, x-rays
*intrauterine infections: HIV, syphilis, rubella, zika
what does reproductive cloning require
an undifferentiated cell
what is reproductive cloning and what are the two methods
- producing a “copy” of the entire organism
- requires a completely undifferentiated cell as the starting point
2 methods:
1. embryo splitting
2. somatic cell nuclear transfer
what is the procedure and results of embryo splitting
procedure:
- egg is fertilized in vitro, and allowed to divide to the 8-cell stage
- then carefully separated and implanted into surrogate mother where it develops
results: clones are genetically identical to each other but not to either parent
embryo splitting
produces identical offspring
*HAS NOT BEEN TESTED ON HUMANS
what is a somatic cell
-any cell other than a gamete
- has a full diploid set of chromosomes
procedure and result of somatic cell nuclear transfer
procedure
- somatic cell from the adult organism to be cloned in inserted into an enucleated fertilized egg
- an electrical current is used to fuse the cells
- fused cell is implanted into uterus of surrogate mother and allowed to develop
Result: offspring is a clone of the adult organism that provided the somatic cell
somatic cell nuclear transfer produces
a clone of an adult
therapeutic cloning creates
tissues and organs
what is the purpose of therapeutic cloning
-cloning of human cells specifically for treating diseases or conditions in patients
- removes a single cell from a patient and nurture it to develop and differentiate into the cell type needed to treat the disease
-potential for creating new cells, tissues or organs
what do polar bodies do
-signaling in nature, release hormones
what comes from the same precursor
skin cells and neurons
what can the cell cycle do and what does it need
-can amplify the mass and needs checkpoints
what is essential to regulating checkpoints
cyclins-regulates progression through the cell cycle checkpoints
how do cells reproduce
by dividing into two
cell division in multicellular organismsenables what
-enables growth from a fertilized egg to a multicellular individual
for humans 1 fertilized cell-> 10 trillion cells
what is cell division followed by
differentiation
- cells become different from each other and from the parent cell and more specialized
what are the two major phases of the cell cycle
-interphase (between cell division)
- mitotic phase (cell division)
stages of interphase and what is interphase
- long growth period between cell divisions
*G1 (first gap)….primary growth phase, very active growth
*S (synthesis)…synthesis of DNA for next cell division - G2 (second gap)…final growth phase before cell division
what is the purpose of the cell cycle
to produce new cells
what occurs during mitotic phase (cell division phase)
*mitosis
- nuclear division…duplicated DNA is distributed between two daughter nuclei
*cytokinesis
- cytoplasm divides
- two new daughter cells are formed
how long does the complete cell cycle take
18-24 hours
*mitosis and cytokinesis takes less than one hour of the complete cell cycle
non dividing is often referred to as
post mitotic
what is G0
non dividing state
- many cells enter this state either temporarily or permenantly
ex. neurons and osteocytes enter G0 after adolescence
chromatin
-dna is loose and diffuse
- this is the trhoughout most of the cell cycle
what is human dna organized into
-46 separate chromosomes containing 3 billion base pairs of dna
what are chromosomes made of
DNA and histones (proteins)
what is DNA compacted into during mitosis
-chromosomes that are visible under the microscope, consisting of 2 sister chromatids joined at the centromere
what a is gene
a short segment of DNA that contains the code for a protein
-there are 20,000-21,000 gens on the 46 chromosomes
which processes are essential to DNA function:
*replication: process of copying the cell’s DNA prior to cell division
* transcription: process of creating a coded message (working copy) of a single gene in RNA that can be carried out of the nucleus (messenger RNA)
* translation: process of using the coded message (mRNA) to assemble amino acids into proteins useful to the cell
what is dna replication
-process of copying DNA prior to cell division
-involves making exact copies of all 46 chromosomes
steps of dna replication
- dna uncoils and “unzips” pulling apart the two strands
- a new complementary strand on DNA is built upon each template strand, using appropriate base-pairing (T-A and G-C)
- DNA polymerase: major replicating enzyme
what is a mutation
alteration in nucleotide sequence of DNA
- sometimes results from errors during replication
- may be caused by physical or chemical forces
somatic cell mutations
may affect the function of tissues or cause cancer
-NOT passed on
gamete mutation
passed on to future generations
mechanism of DNA repair
-enzymes recognize errors in dna sequence
- errors are cut out with enzymes
- damaged section is replaced
- DNA backbone is reconnected
- numerous different DNA repair enzymes are needed
when are repair enzymes the most active
between the time of DNA replication and the beginning of mitosis
-mutations in certain genes that code for DNA repair enzymes lead to increased risk of cnacer
transcription
*process of copying DNA of a gene into mRNA (messenger ribonucleic acid)
*occurs within the cell nucleus
*the mRNA is a working copy of the gene(recipe) that will leave the nucleus to be translated at ribosomes
translation
-process of using mRNA template to direct the synthesis of a protein
-occurs in the cytoplasm at ribosomes
summarized what is transcription
converting a gene’s code into mRNA
steps of transcription
- DNA of a gene unwinds
- RNA polymerase assists in copying DNA nucleotide sequence into a polymer of RNA nucleotides
- primary transcript (RNA) made, included introns (intervening sequences) and exons
- introns edited out by catalytic RNAs called riboenzymes
- exons(carry genetic info) are spliced appropriately
- messenger RNA strand is the result
genetic code
*genetic code is a triplet code
*codon
-sequence of 3 mRNA bases
-codes for specific amino acid
*redundancy of the genetic code
- 64 diff codons but 20 diff amino acids
-several diff codons encode each amino acid, with the exception of methionine (AUG, start codon)
stop codons
UAA, UAG, UGA
summarize what translation does
makes a protein from mRNA
components of translation
*messenger RNA (mRNA): copy of the “recipe”
- specifies the order of amino acids in a protein by means of a series of 3-base codons
*transfer RNA (tRNA): relatively small RNA molecules that escort amino acids to the ribosome
- tRNA has anticodons that will pair with complementary codons in mRNA
*ribosomes made of ribosomal RNA (rRNA) and protein:
-contains sites for mRNA and incoming amino acid-tRNA
- contains the enzymes/factors that catalyze the peptide bond formation
3 steps of translation
- initiation
-initiator tRNA (carring AUG…methionine), start codon on mRNA and ribosomal subunits form an initiation complex - elongation
- tRNA brings specific amino acids to developing protein chain
-chain elongates one amino acid at a time - termination
- stop codon terminates developing chain, protein is released from ribosome
the cell cycle consists of 2 periods
interphase and mitotic phase
