Unit 6 Flashcards
When would a cell divide? (4)
- growth of multicellular organism
- replacement of damaged cells
- embryonic development
- asexual reproduction in prokaryotes
What is the name of the cell division for a prokaryote?
binary fission
Why don’t eukaryotes divide by binary fission?
Eukaryotic cells are more complex and have more DNA
Cell Cycle
series of events that take place in a eukaryotic cell as it grows and divides
What are the phases of interphase? (3)
- G1
- Synthesis (S)
- G2
What happens in G1? (3)
- organelles produced
- proteins made (for DNA synthesis)
- growth
What happens in S phase? (2)
- DNA replication
- Sister chromatids form (chromatin form)
What happens in G2?
-proteins made for (nuclear and cytoplasmic division)
Sister Chromatid
either of two identical copies of DNA (made during S phase) attached to one another by a centromere
Centromere
attaches sister chromatids
Chromatin
DNA wrapped around histone proteins
Mitosis
division of the eukaryotic nucleus
What are the 4 stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
What happens in prophase? (3)
- centrosomes move to opposite poles of the cell and form spindle fibers
- Sister chromatids (chromatin) condenses into replicated chromosomes
- nuclear membrane breaks down
Replicated Chromosome
two, identical sister chromatids attached by a centromere
What happens in metaphase? (2)
- Spindle fibers attach to kinetochores
- Contraction of the spindle fibers causes the replicated chromosomes to line up along the center of the cell
What happens to sister chromatids in anaphase?
They become single chromosomes
What happens in anaphase? (2)
- Continued contraction of the spindle fibers causes separation of sister chromatids
- Single chromosomes move to opposite poles of the cell
What happens in telophase? (4)
- nuclear membranes form
- fibers disappear
- Chromosomes arrive at poles
- Chromosomes uncoil
Cytokinesis
division of the eukaryotic cytoplasm to form 2 daughter cells
What is seen as cytokinesis occurs in an animal cell?
cleavage
Cleavage (2)
- contractile proteins pinch cell apart
- cleavage furrow appears
What is seen as cytokinesis occurs in a plant cell?
cell plate
Cell Plate
material deposited from vesicles to form cell plate and then cell wall
How does prophase ensure that daughter nuclei are genetically identical?
Chromatin condenses so DNA doesn’t get lost/damaged
How does metaphase ensure that daughter nuclei are genetically identical?
replicated chromosomes line up at equator with one copy facing each pole
How does anaphase ensure that daughter nuclei are genetically identical?
Chromatids are pulled apart/the right # are pulled in each direction
How does telophase ensure that daughter nuclei are genetically identical?
chromosomes reach poles and newly forming nuclei allow the cell to divide while ensuring no chromosomes are caught on the wrong side
When do cells stop dividing? (2)
- when detached from a surface
- when they touch/get crowded and competition increases
What triggers cells to divide? (2)
- size
- growth factor
Size
large cells divide (SA:Volume too low)
Growth Factor
chemicals released by cells that encourage other cells to divide
What controls the cell cycle and division?
cyclins
Cyclin
proteins released in the cell in response to growth factor binding that control the cell cycle
How many cyclins are there for the cell cycle?
4
What do cyclins do during the cell cycle?
rise and fall
What do high levels of cyclin do?
activate target molecules that move cells into the next stage of the cycle
How do cyclins control the the cell cycle? (4)
1) Cyclins bind to enzymes called cyclin-dependent kinases (Cdk’s)
2) Cdk’s phosphorylate proteins (add phosphate) in the cell
3) Phosphorylation activates proteins to carry out tasks (specific to one of the phases of the cell cycle)
4) Cyclins is broken down (cyclin level falls)
What makes cancer cells different?
they do not respond to normal cell cycle regulation
What causes cancer?
damaged/mutated genes
Mutation
change in the base sequence of a gene
Mutagen
agents that cause gene mutations
Carcinogens (2)
- agents that cause cancer
- mutagens or other factors that accelerate cell division
What are examples of mutagens? (3)
- high energy radiation
- short-wave ultraviolet light
- viruses
What do proto-oncogenes and tumor suppressor genes control?
the cell cycle by coding for cyclins, CDKs, or other proteins
What happens when proto-oncogenes and tumor suppressor genes are mutated?
the cell cycle is disrupted
Oncogene
mutated gene that contributes to the development of a tumor
Tumor
abnormal growth of tissue
Benign (4)
- less harmful
- won’t spread
- fewer mutations
- retain normal functions
Malignant (3)
- harmful/cancerous
- can spread
- cell mutations accumulate
Primary Tumor
a malignant tumor growing at the site where the abnormal growth first occurred
Metastasis
the movement of cells
Secondary Tumors
The circulating cancerous cells invade tissues at a different locations and develop
How does a primary tumor become a secondary tumor? (4)
1) A primary tumor grows at the site where the abnormal growth first occurred
2) Cancerous cells can detach from the primary tumor
3) Cancerous cells gain penetrate the walls of lymph or blood vessels and circulate around the body
4) Cancerous cells invade tissues at different locations and develop, by uncontrolled cell division, into a secondary tumors
Asexual Reproduction
offspring produced with DNA from one parent
Prokaryotic Cells
reproduction is asexual using binary fission
Sexual Reproduction
offspring produced with DNA from two parents who contribute half each
What is another name for sex cells?
gametes
What is formed at the result of the union of gametes?
a zygote
Diploid Cell
two complete sets of chromosomes (2n)
What are examples of diploid cells? (2)
- Zygotes
- Body Cells
What is another name for a body cell?
somatic cell
Haploid Cell
one complete set of chromosomes (n)
What are examples of haploid cells? (2)
- Sperm
- Egg
Meiosis
special type of cell division in reproductive organs that forms haploid sex cells (half the # of chromosomes) from diploid body cells
Meiosis I
homologous chromosomes are pulled apart (reduction phase)
Meiosis II
separates sister chromatids (separation phase)
How many haploid cells come from diploid cells in meiosis?
4
Interphase (Meiosis)
DNA is replicated before meiosis to produce 2 copies of genetic info each from the female and male parent
Prophase I (5)
- Chromatin condenses
- synapsis
- nuclear envelope disappears
- spindle microtubules form
- centrosomes move to opposite poles
Synapsis
pairing of homologous chromosomes to form a tetrad
Tetrad
two homologous chromosomes (four chromatids) joined together
Metaphase I (2)
- spindle microtubules attach to centromeres
- Tetrads align at metaphase plate
Anaphase I
- Homologous chromosomes separate and move toward opposite poles of the cell
Telophase I (4)
- Chromosomes reach poles
- Chromosomes decondense
- nuclear membrane may reform
- Cytokinesis occurs with telophase I and two haploid cells are formed
Why is meiosis II similar to mitosis?
sister chromatids of each chromosome separate
What does sexual reproduction allow for? (2)
- characteristics from both parents to appear in offspring
- leads to varied offspring/genetic diversity
What is the benefit of genetic diversity?
it favors survival of a species in a changing environment
What do the variations in Meiosis accomplish?
producing gametes which are all different
How is variation accomplished in Meiosis? (2)
- crossing-over
- independent assortment
Crossing over (prophase I)
parts of nonsister homologous chromatids break and then swap alleles when homologous chromosomes form tetrads
Chiasma (4)
- a site of crossing over
- an X-shaped structure
- visible when homologous chromosomes unpair
- holds homologs together until anaphase
Recombination
production of gene combinations different from those carried by original chromosomes
Parental Chromosome
same combination of alleles as parent
Recombinant Chromosome
different combination of alleles from parent
Independent Assortment (Metaphase I)
tetrads are randomly arranged in the center of the cell during metaphase I and meiosis independently/randomly distributes chromosomes into cells
What does the “n” represent in 2^n?
haploid #
What does 2^n represent?
The total # of combinations of chromosomes that meiosis can package into gametes
What does the fusion of gametes result in?
genetic variation
True or False: the gametes in an individual are genetically different?
true
How do karyograms organize chromosomes? (3)
- size
- DNA staining pattern
- location of centromeres
When are pictures for karyograms taken?
metaphase of mitosis
What are two ways to get fetal cells to detect disorders before birth?
- amniocentesis
- chronic villus sampling
Amniocentesis (mainly used) (2)
- removes amniotic fluid
- 2nd trimester
chorionic villus sampling (CVS) (2)
- removes piece of chorionic villi (placenta)
- 1st trimester
What are the advantages of amniocentesis? (2)
- it can detect nearly all chromosomal abnormalities
- lower risk
What are the advantages of chronic villus sampling? (2)
- nearly all chromosomal abnormalities are detected
- can be performed earlier
When is a woman a candidate for genetic testing?
at age 35 or older
Why is an older women a candidate for genetic testing?
The possibility of having a baby with a chromosomal defect increases with the age.
Trisomy
individual/cell has an extra chromosome
Monosomy
individual/cell lacks a chromosome
What is an example of a trisomy?
down syndrome
Down Syndrome
pair 21 has 3 chromosomes instead of 2 (trisomy 21)
Turner Syndrome
females lack second X chromosome
What do errors in meiosis lead to?
gametes with abnormal numbers of chromosomes
Nondisjunction
failure of chromosomes or chromatids to separate during meiosis
What happens with nondisjunction during meiosis I?
Homologous pairs fail to separate in meiosis I due to incorrect spindle fiber attachment
What happens with nondisjunction during meiosis II?
Sister chromatids fail to separate during meiosis II due to centromeres not dividing
clone
group of genetically identical organisms or cells.
What is a naturally occurring cloning system in prokaryotic cells?
binary fission (asexual)
What is a naturally occurring cloning system in eukaryotic cells? (3)
- budding
- fragmentation
- vegetative propagation
Budding
Cells split off to make organism
Fragmentation
organisms grow from fragment of parent
Vegetative Propagation
small pieces of plants are induced to grow independently
tubers or runners
What can the rooting of stem cuttings produce?
clones
Stem cutting
growing plants using portions of stems
How can sexually reproducing organisms create clones?
Monozygotic (identical) twins
What are two ways animals can be cloned through biotechnology?
- embryo splitting
- nuclear transfer
embryo splitting
breaking up multicellular embryo into more than one group of cells at an early stage of development to generate “twins”
Why is embryo splitting possible?
Embryonic cells retain pluripotency (can become any type of tissue) at early stages (8 cells or less)
Somatic Nuclear Cell Transfer (SCNT)
creates embryo from a differentiated somatic cell and an egg cell
What are the steps of SCNT? (4)
- Diploid somatic cells are removed from a donor
- The nucleus of an unfertilized egg (haploid) is removed
- The egg cell is fused with the diploid nucleus
- The new diploid cell is implanted in a surrogate’s uterus
How does SCNT differ from the natural way of making an embryo? (2)
- Natural: sperm and egg join to produce zygote with 2 sets of chromosomes (diploid)
- SCNT (reproductive cloning): 2 sets of chromosomes in zygote come from somatic cell donor
What are the 2 main purposes of SCNT?
- reproductive cloning
- therapeutic cloning
Reproductive Cloning
If the embryo is implanted into the uterus of a surrogate, a new cloned organism will develop
Therapeutic Cloning
involves producing embryos from which embryonic stem cells can be harvested for medical use
What are arguments in support of therapeutic cloning? (4)
- any procedure that reduces pain and suffering is justified
-stem cells can be used to replace organs/tissues that have been lost/damaged in a patient
-pain and suffering can be reduced/lives can be saved
-cells are removed when no pain is felt by the embryo
What are arguments against therapeutic cloning? (4)
-there is danger of embryonic stem cells developing into tumor cells/harmful effects are not yet known;
-every human embryo is a potential human with the right to development;
-more embryos may be produced than can be used and so some would be killed;
-any procedure that harms a life/kills is unethical
