D2.1 Cell and Nuclear Division Flashcards
What is the basic structural unit of all living organisms?
Cells
Cells are the fundamental building blocks of all living things.
What term is used to refer to the parent cell in cell division?
Mother cell
The terms ‘mother’ and ‘daughter’ are identifiers, with no implication of gender.
What process do prokaryotic cells, such as bacteria, use to divide?
Binary fission
What type of nuclear division do eukaryotic cells undergo?
Mitosis
What type of nuclear division creates gametes in eukaryotic organisms?
Meiosis
What is cytokinesis?
The process of splitting the cytoplasm between daughter cells
How do animal cells achieve cytokinesis?
Through the formation of a contractile ring of actin and myosin proteins
What structure forms in plant cells during cytokinesis?
Cell plate
What is the significance of equal cytoplasmic division in cytokinesis?
Ensures both daughter cells are the same size and have the same structure and function
What is oogenesis?
The process of producing mature egg cells or ova in humans
What happens to the first polar body during oogenesis?
It usually disintegrates and is re-absorbed by the body
What is budding in yeast?
A type of asexual reproduction involving the outgrowth of a genetically identical daughter cell
What is the role of mitosis in eukaryotic cells?
Produces diploid daughter cells for growth and repair
What type of cells does meiosis produce?
Haploid genetically unique daughter nuclei
What is the significance of crossing over in meiosis?
It leads to genetic variation in the daughter cells
What must occur before mitosis or meiosis?
DNA replication
What are sister chromatids?
Two genetically identical elongated DNA molecules held together by a centromere
What is the basic building block of chromatin?
Nucleosome
What role do microtubules play in cell division?
They form the spindle apparatus to move chromosomes
What is the key difference between mitosis and meiosis?
Mitosis produces 2 identical cells; meiosis produces 4 unique cells
What is mitosis?
A type of nuclear division that produces two genetically identical diploid daughter nuclei for somatic cells.
List the four stages of mitosis.
- Prophase
- Metaphase
- Anaphase
- Telophase
Prophase?
- Chromatin condenses into chromosomes.
- microtubule organising cnetres (plants)
- centrosomes (animals)
What occurs during metaphase?
Sister chromatids line up on the metaphase plate.
* spindle attaches to cnetromere
* each centromer attached to both poles
What is the function of spindle fibres during anaphase?
They shorten, splitting the centromere and pulling sister chromatids apart to opposite poles.
What happens during telophase?
Chromosomes decondense
nuclear membrane reforms
spindle fibres disintegrate.
What is meiosis?
A type of nuclear division that produces four haploid genetically unique daughter nuclei. (reduction didvision)
What occurs during prophase I of meiosis?
The nuclear membrane disintegrates
homologous chromosomes form bivalents & crossing over
What is crossing over?
The exchange of equivalent segments of DNA between non-sister chromatids.
What are homologous chromosomes?
Chromosomes that are similar in size and shape and contain the same genes at the same loci.
What occurs during metaphase I?
Spindle fibres pull bivalents to the center of the cell with random orientation/independent assortment
What happens in anaphase I?
spindle fibres shorten
Homologous chromosomes are separated and pulled towards opposite poles.
* sister chromatids remain connected
What is produced at the end of meiosis I?
Two non-identical haploid daughter cells.
What occurs during telophase I?
Homologous chromosomes reach the poles
nuclear membrane forms.
What happens during prophase II?
DNA recondenses and the nuclear membrane disintegrates.
What is the outcome of meiosis II?
Four haploid daughter cells are created.
What is non-disjunction?
A genetic error during meiosis where chromosomes fail to separate properly.
What can result from non-disjunction?
Trisomy (three chromosomes) or monosomy (one chromosome).
What is Trisomy 21?
A condition resulting from an extra copy of chromosome 21, also known as Down syndrome.
What is Turner’s syndrome?
A monosomy X condition due to the absence of one X chromosome.
What is karyotyping?
A genetic testing technique that analyzes the number and structure of chromosomes.
How does meiosis contribute to genetic diversity?
Through crossing over, random orientation, and independent assortment.
What are chiasmata?
The points of crossing over between non-sister chromatids.
What is random orientation in meiosis?
The independent arrangement of homologous chromosomes at the equator during metaphase I.
What is the formula to calculate possible combinations after meiosis I?
2^n, where n is the haploid number.
What does random fertilization increase?
The possible genetic combinations in offspring.
What is cell proliferation?
The process of cellular division and replication.
What are meristems?
Regions of undifferentiated cells with the potential to become any cell type in the plant
What stimulates cell division in meristems?
Auxin
What type of meristems are located at the tips of roots and shoots?
Apical meristems
What is the process called that occurs during early human embryonic development?
Cleavage
What are the cells called that result from the division of the fertilized egg?
Blastomeres
What is the cell cycle?
A sequence of events including interphase, mitosis, and cytokinesis
What are the three phases of interphase?
- Growth phase 1 (G1) * Synthesis (S) * Growth phase 2 (G2)
What occurs during the G1 phase of the cell cycle?
The cell grows in size and carries out normal metabolic functions
What happens during the S phase of the cell cycle?
DNA replication occurs
What is the main function of the G2 phase?
Preparation for mitosis and ensuring accurate DNA replication
What are cyclins?
Cyclins are a family of proteins that regulate the cell cycle.
Cyclins activate cyclin-dependent kinases (CDKs) to drive the cell cycle forward.
How do cyclins control the cell cycle?
Cyclins bind to and activate cyclin-dependent kinases (CDKs) which phosphorylate specific proteins to drive the cell cycle forward.
Each cyclin is active during specific stages of the cell cycle.
What is the threshold concentration in the context of cyclins?
The threshold concentration is the specific level that a cyclin must reach for the cell to progress to the next stage of the cell cycle.
Example: Cyclin E binds to a CDK just before the S phase of interphase.
What happens to the cyclin–CDK complex after it completes its task?
The cyclin is degraded and the CDK is deactivated.
The cell cycle then continues to the next stage with a different cyclin.
What are proto-oncogenes?
Proto-oncogenes are genes that code for proteins promoting cell growth and division.
Mutations can turn them into oncogenes, leading to uncontrolled cell division.
What are tumor suppressor genes?
Tumor suppressor genes code for proteins that slow down or prevent cell division and promote apoptosis.
Mutations in these genes can lead to uncontrolled cell division.
What can uncontrolled cell division lead to?
tumor.
Tumors can be cancerous or non-cancerous.
What are benign tumors?
Benign tumors are growths of abnormal cells that are not cancerous and tend to grow slowly.
They have well-defined borders and do not spread to other parts of the body.
What are malignant tumors?
Malignant tumors are cancerous, grow rapidly, and can spread to other parts of the body through metastasis.
They often lack well-defined borders.
What is metastasis?
Metastasis is the process by which malignant tumors spread to other parts of the body.
The original tumor is called the primary tumor, while the spread is termed secondary tumors.
What is the mitotic index?
The mitotic index is a measure of the proportion of actively dividing cells in a population.
It is expressed as a value between 0 and 1 or as a percentage.
How is the mitotic index calculated?
dividing the number of actively dividing cells by the total number of cells and multiplying x100
This formula reflects cell proliferation and growth rate.
What does a high mitotic index indicate?
A high mitotic index indicates that a tumor is rapidly growing and is more likely to spread.
It is often elevated in tumorous tissue.
Describe the following process
oogenesis
- unequal distribution of cytoplasmic contents through a series of cell divisions.
- primary oocyte undergoes two rounds of cell division, resulting in the production of a secondary oocyte and the first polar body
- The secondary oocyte is larger than the first polar body and receives most of the cytoplasmic contents, including organelles, ribosomes and energy stores.
- If fertilisation occurs, the secondary oocyte undergoes a second round of cell division, producing a mature ovum (egg cell) and a second polar body.
budding
A = centromere
B= sister chromatids
anaphase
prophase
telophase
metaphase
Prophase 1
* each set of parental chormosomes form sister chormtids
* bivalent/tetrad => homologous pair
* crossing over
metaphase 1
anaphase 1
telophase 1
prophase 2
cytokinesis 2
metaphase 2
* align in centre
* random orientation
anaphase 2
telphase 2
non disjunction in meiosis 1
* you pulled 2 X’s in one cell and only 1 X’s in other cell
=> diviuded again to give this
Non disjunction in meiosis 2
* you pulled one WHOLE X and one leg into one cell
* you pulled only one leg into other
- you have 2 normal ones
due to non disjunction in meiosis 1
2x monosomy
2x trisomy
due to non disjunction in meiosis 2
2x normal
1x trisomy
1x monosomy
random orientation
* metaphase 1
* chromosomes take up random positionings
formula to calculate no of different combinations produced at end of meiosis
2^n (n= haploid number)
