Week 3 Lecture: Plant Cell Cycle (Mitosis and Meiosis) Flashcards
Dictated by continuous generation of new cells. Achieved through cell expansion and cell division
Growth
Thread-like structures in a cell’s
nucleus that are visible under the microscope only during cell division. Consists of proteins and a single large molecule of DNA that contains hundreds of
thousands of different gene.
Chromosomes
How many chromosomes does a cabbage have?
20 chromosomes per cell (10 pairs per cell)
How many chromosomes does a Haplopappus gracilis have?
4 chromosomes per cell (2 pairs per cell)
How many chromosomes does a Olea europea have?
46 chromosomes (23 pairs per cell)
How many chromosomes does a Ophioglossum reticulatum have?
1262 chromosomes per cell (631 pairs
per cell)
Members of a chromosome pair that are similar in size, shape, and genetic constitution. Carry information governing the same genetic traits, although is not necessarily identical.
Homologous chromosomes
A ___ carrying a gene that specifies flower color, but each chromosome may specify different colors of petals.
homologous pair
A cell in which each chromosome occurs in pairs.
Diploid (2n)
A cell that has a single set of chromosomes.
Haploid (n)
- Two chromosomes
- Represented by 2n
- Somatic cells
- Created by Mitosis
Diploid
- Single chromosome
- Represented by n
- Gametes
- Created by Meiosis
Haploid
The ___ is the successive series of events in the life of a dividing eukaryotic cell.
cell cycle
What are the two main phases of the cell cycle?
Interphase and M phase
Often represented as a circle and consists of two main phases (interphase and M phase)
Cell cycle
The period between two successive
divisions, represented by a complete revolution of the circle, is the ___.
generation time
- Preparatory phase
- Performs Cell growth and DNA
duplication
Interphase
- Mitosis
- Meiosis I
- Meiosis II
M (Mitosis/Meiosis) Phase
Localized areas of the plant body where mitosis and cytokinesis take place most of the time. Occur in the shoot and root tips (the apical meristems) and in some plants, in thin cylindrical regions that run the entire lengths of stems and roots except at the tips (the lateral meristems)
Meristems
Allows the production and subsequent
elongation of new cells, causing an increase to the length of growing stems and roots. Occur to the shoot and roo t tips.
Apical meristems
Produce additional wood and bark tissues that
add girth and thickening or widening to stems and roots of trees and shrubs. Occurs in thin cylindrical regions that run the entire lengths of stems and roots except at the tips
Lateral meristems
The stage *between *successive cell divisions or the between phases. The cell synthesizes needed materials and grows. Chromosomes undergo duplication during this phase although not readily visible.
Interphase
What are the subphases of the interphase?
- Gap I Phase (GI Phase) or Pre-synthesis gap
- Synthesis phase (S Phase)
- Gap II (GII Phase) or Post-synthesis
- Second stage of Interphase
- Duplication of nucleus
- Synthesis of DNA and protein
- “Replicated chromosomes”- chromosomes after
- S phase
Interphase: Synthesis Phase (S)
- First stage in Interphase
- Pre-synthesis phase
- Cell growth
- Duplication of organelles
- Cell’s nucleus contains single
- nucleolus and light chromatin
- materials
- Does not involve DNA
- replication
- GI checkpoint
Interphase: First Gap Phase (G1)
- Third step, next to S Phase
- Post-synthesis phase
- Allows the cells to grow more
- More proteins and organelles (e.g.mitochondria,
chloroplasts, etc.) are being made - Larger nucleus; nucleus contain two nucleoli and darker chromatin materials.
- Prepares the cell for the actual division (M Phase)
Interphase: Secondary Gap Phase (G2)
- Gap zero phase or Resting Phase
- Cells may opt to enter this phase or may
directly enter the G1 phase up to cell division
➢ Intrinsic and extrinsic factors (resource availability, nutritional deprivation, etc.) - A cell is performing its function without actively preparing to divide
- Quiescent stage
➢ Cells enter G0 phase, phase
temporarily - Senescent stage
➢ Cells enter G0 phase permanently
Interphase: Gap Zer0 Phase (G0)
Cells enter G0 phase, phase
temporarily
Quiescent stage
Cells enter G0 phase permanently
Senescent stage
What are the important processes under Interphase?
- DNA Replication
- Transcription
- Translation
A process of duplicating DNA through semi-conservative replication. Initiation, Transcription, and
Translation
DNA Replication
The genetic information in the DNA is transferred to RNA through the catalytic action of RNA polymerase
Translation
Translation is the synthesis of a protein from an mRNA template. Synthesize proteins, which are used for millions of cellular functions
Translation
Indicates or signals the completion of interphase. Visible changes associated with the division of the nucleus take place. Most cellular activities (e.g. Protein synthesis) are suspended during this phase
Mitosis
What are thr four stages of the M Phase?
- Prophase
- Metaphase
- Anaphase
- Telophase
__ is a carefully controlled process that organizes and separates the chromosomes correctly. After the cells separate the chromosomes and build new nuclei, they divide their cytoplasm by cytokinesis and form two distinct cells.
Mitosis
The portion of the chromosome centromere to which the mitotic spindle fibers attach.
Kinetochore
Prophase
- Chromatin condenses into duplicated chromosomes consisting of two chromatids attached at centromeres.
- Chromosomes become shorter and thicker and individually visible under a compound light microscope.
- Nuclear envelope disappears. The nucleolus shrinks and disappears
- Spindle microtubules attached to kinetochores and chromosomes move toward midplane.
Prophase
A specialized region of a chromosome.
At prophase, sister chromatids are joined in the
vicinity where they are located.
Centromere
Function in chromosome distribution
during mitosis.
Microtubules
Small, membrane-enclosed sacs
Vesicles
The structure consisting mainly of microtubules that provides the framework for chromosome movement during cell division
Spindle
- The spindle microtubules grow and shrink as they move toward the center of the cell in a “search and capture” process.
- If a microtubule comes near the centromere of a chromosome, the microtubule “captures” it.
- As the now-tethered chromosome continues moving toward the cell’s midplane, a spindle microtubule from the cell’s other pole attaches to the opposite side of the centromere.
Mitosis: Prophase
- This phase* begins as the sister chromatids separate.*
- Sister chromatids (now called chromosomes) separates and move to opposite ends of the cell.
- Ends when all the chromosomes have reached
the poles
Mitosis: Anaphase
- The division of the cytoplasm that usually
accompanies mitosis, generally begins during
telophase. - Occurs by the formation of a cell plate, a partition
between the newly formed nuclei in the equatorial
region of the cell. - Forms two daughter cells.
Cytokinesis
- Duplicated chromosomes *line up on the midplane of the cell
- Mitotic spindle is completely visible and composed of numerous microtubules that extend from pole to pole.
- Each chromatid is quite condensed and appears thick and distinct.
- Individual chromosomes are more distinct in this phase
Mitosis: Metaphase
- The final stage of mitosis in which chromosomes arrive at the poles and return to their interphase condition.
- The chromosomes begin to elongate by uncoiling and then become invisible chromatin threads
- Two separate nuclei form.
Mitosis: Telophase
-
Reproductive cells (egg and sperm cells) which
have half the diploid number of chromosomes. - Form a complete, new organism by uniting
Gametes
Reduces the number of chromosomes in reproductive cells by half. It means “to make smaller”
Meiosis
As a result of ___, each gamete has only one
chromosome of each pair, resulting in an egg or sperm cell with a haploid, or n, number of chromosomes.
meiosis
A fertilized egg produced upon union of the
female gamete (egg) and the male gamete (sperm
cell).
Zygote
___ separates the members of each homologous pair of chromosomes. No two offspring of the same parents will be exactly alike
Meiosis
What are the two cell divisions that meiosis consists of?
First and second meiotic
divisions (meiosis I and meiosis II)
- The chromosomes duplicate during the S Phase of Interphase before the complex movements of meiosis actually begin.
- The homologous chromosomes come
together to lie side by side lengthwise and synapse, crosing over takes place. - A spindle forms consisting of microtubules.
- The nuclear envelope and nucleolus disappear
- In cells with large chromosomes, the association of the four chromatids of each
Meiosis I: Prophase I
Pairing of homologous
chromosomes
Synapsis
- The sharing of genetic material between two non-sister chromatids of paired homologous chromosomes
- Produces new combination of genes.
Crossing over
- Homologous chromosomes line up in pairs along the midplane.
- Both kinetochores of one duplicated chromosome are attached by spindle microtubules to the same pole.
- Both kinetochores of the duplicated homologous chromosome are attached to the opposite pole
Meiosis I: Metaphase I
- The paired homologous chromosomes separate, with one chromosome moving toward one pole and its homologue moving toward the other pole.
- Sister chromatids remain attached at their centromeres.
- Each pole receives a random combination of maternal and paternal chromosomes, but only one member of each homologous pair is present at each pole.
Meiosis I: Anaphase I
- There would be two duplicated chromosomes,
one of each homologous pair, at each pole. - The nuclei often reorganize, the chromatids generally elongate, and cytokinesis may take place.
Meiosis I: Telophase I
___ are formed at the end of Meiosis I.
Two haploid cells
- Sister chromatids separate and chromosomes condense again.
- There is no pairing of homologous chromosomes and no crossing over occurs.
- Main features: Chromosomes become shorter and thicker, and their two-stranded nature once
more becomes apparent.
Meiosis II: Prophase II
- The chromosomes, each consisting of two sister chromatids, line up on the midplanes of their cells
- There are two chromatids of a
single chromosome - Main features:
1. The centromeres of the chromosomes
become aligned along the equator.
2. New spindles become conspicuous
and complete.
Meiosis II: Metaphase II
- The paired chromosomes separate, with one chromosome moving toward one pole and its homologue moving toward the other pole.
- Only one member of each homologous pair is present at each pole.
- Main features: The centromeres and chromatids of each chromosome separate and migrate to opposite poles
Meiosis II: Anaphase II
Main features:
1. The coils of the chromatids (now called
chromosomes again) relax so that the
chromosomes become longer and
thinner.
- New nuclear envelopes and nucleoli reappear for each group of chromosomes.
Meiosis II: Telophase II
Result in four haploid daughter cells, each containing one of each kind of chromosome. Each resulting haploid cell has a different combination of genes.
Meiosis I and Meiosis II
- There is one member of each homologous chromosome pair at each pole. Each chromosome is in an unduplicated state.
- *Nuclear enveloped then re-form *around each set of chromosomes.
- The chromosomes gradually elongate into threadlike chromatin.
- Cytokinesis occurs.
Meiosis II: Telophase II
Two sources of genetic variation:
1. DNA segments are exchanged between maternal and paternal homologues during crossing over
- During Meiosis, the maternal and paternal chromosomes of homologous pairs separate independently so that each member of a pair is randomly distributed to one of the poles at anaphase.
Meiosis I and Meiosis II
