Mod 2 Chap 6: Cell Division, Diversity & Differentiation Flashcards Preview

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Flashcards in Mod 2 Chap 6: Cell Division, Diversity & Differentiation Deck (59)
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Describe the cell cycle.🌟

- highly ordered sequence of events
- takes place in a cell, resulting in division of cell + formation of two genetically identical daughter cells
- has two main phases (in eukaryotes): interphase, and mitotic (division) phase (= mitosis / meiosis)


Generally describe Interphase.🌟

- long periods of growth and normal working separate divisions where a cell is NOT dividing
- although aka 'resting phase', interphase actually = a v active phase, when cell is carrying out all major functions e.g. Producing enzymes / hormones + preparing cell for division
- has three stages within itself: G1, S + G2


Describe what occurs in the stage of Interphase as a whole.🌟

- DNA replicated + checked for errors in nucleus
- protein synthesis occurs in cytoplasm
- mitochondria grow + divide in plant + agal cell cytoplasm
- normal metabolic processes of cells occur


Describe what occurs in the separate stages within Interphase.🌟

G1 (first growth phase): proteins from which organelles are synthesised are produced + organelles replicate, cell increases in size

S (synthesis phase): DNA replicated in nucleus

G2 (second growth phase): cell continues to increase in size, energy stores increase + duplication of DNA is checked for errors


Generally describe the mitotic phase.🌟

- period of cell division
- two stages of cell division: Mitosis (nucleus divides), and Cytokinesis (cytoplasm divides + two cells produced)


Describe the 'G0' phase of the cell cycle.

- phase where cell leaves the cycle (temporarily / permanently)

Reasons this happens:

- differentiation: a cell specialised to carry out a function is no longer able to divide, as carries out this function indefinitely + does not enter cycle again
- DNA of cell maybe damaged: meaning it's no longer viable, damaged cells cannot divide and enters period of permanent cell arrest (G0), normal cells only divide limited no of times before becoming senescent
- age: ageing = no of senescent cells in body increasing, this then linked w/ age relating diseases e.g cancer / arthritis


Describe how the cell cycle is regulated / controlled.🌟

- needed to ensure a cell only divides when it has grown to right size, replicated DNA is correct + when chromosomes are in correct positions during mitosis, so to ensure fidelity of cell division (creation of tow identical daughter cells)
- control mechanisms of cell cycle = checkpoints
- checkpoints monitor whether each phase of cycle is accurately completed before cell progresses to next phase
- occur variously throughput cycle: end of G1 phase, end of G2 phase, + in mitosis


Describe the importance of mitosis.🌟

- mitosis = term for entire process of cell division in eukaryotic cells
- refers to nuclear division (essential stage in cell division)
- ensures both daughter cells produced are genetically identical, each new cell has an exact copy of DNA in parent cell + same no of chromosomes
- necessary for asexual reproduction (production or genetically identical offspring from one parent in multicellular organisms + eukaryotic single celled organisms. But prokaryotic organisms have no nucleus so reproduce asexually by diff process: binary fission.


Describe what happens with the chromosomes PRIOR to mitosis.🌟

- all DNA in nucleus has to be replicated in interphase before mitosis can occur
- each DNA molecule (chromosome) converted into two identical DNA molecules called chromatids
- two chromatids then join at region called centromere, so they can be precisely manoeuvred + segregated equally, one each into the two new daughter cells, during mitosis


Name the main stages of mitosis.🌟

4 stages:
- Prophase
- Metaphase
- Anaphase
- Telophase


Describe the Prophase stage of Mitosis.🌟

- chromatin fibres ( = mix of various proteins + DNA + RNA) coil + condense to form chromosomes
- nucleolus (area of nucleus responsible for RNA synthesis) disappears + nuclear membrane breaks down
- protein microtubules form spindle-shaped structures linking poles of cell
- in animal cells + some plant cells; two centrioles migrate to opposite poles of cell
- spindle fibres attach to specific areas on centromeres + move chromosomes to centre of cell
- nuclear envelope has disappeared now


Describe the Metaphase stage of Mitosis.🌟

- chromosomes moved by spindle fibres to form a plane in centre of cell, called metaphase plate, then held in position


Describe the Anaphase stage of Mitosis.🌟

- centromeres holding together chromatid pairs divide
- chromatids then separated + pulled to opposite poles of cell by shortening spindle fibres
- 'V' shape of chromatids moving towards poles is result of them being dragged by centromeres through the liquid cytosol


Describe the Telophase stage of Mitosis.🌟

- chromatids have now reached poles + now called chromosomes
- the two new sets of chromosomes assemble at each pole + nuclear envelope reforms around them
- chromosomes start to uncoil + nucleolus is formed
- cell division / cytokinesis begins


Generally describe Meiosis.🌟

- gametes are formed by meiosis
- nucleus (in meiosis) divides to produce 4 daughter cells (gametes)
- each gamete contains half of chromosome no. of parent cell (it is haploid)
- Meiosis known as reduction division
- each nucleus of organism's cells contains two full sets of genes, so each nucleus gas matching set of chromosomes called homologous chromosomes + so is termed diploid


Describe alleles.

- Diff versions of same gene (aka gene variants)
- the diff alleles of a gene will all have same locus (position on a particular chromosome)


Name and outline the main stages of Meiosis.🌟

- Meiosis involves two divisions: Meiosis 1 and Meiosis 2, each has a single pro, meta, ana and telo phase

Meiosis 1:
- the reduction division where pairs of homologous chromosomes are separated into 2 cells
- each intermediate cell only has one full set of genes instead of 2, so cells are haploid

Meiosis 2:
- second division = similar to mitosis
- pairs of chromosomes present in each daughter cell are separated, forming 2 more cells
- so 4 haploid daughter cells produced in total


Describe the Prophase 1 stage of Meiosis 1.🌟

- chromosomes condense, nuclear envelope disintegrates, nucleolus disappears + spindle formation begins (all same as mitosis prophase)
- also homologous chromosomes pair up, forming bivalents
- chromosomes moving through liquid cytoplasm as they are brought together results in chromatids entangling = "crossing over"


Describe the Metaphase 1 stage of Meiosis 1.🌟

- same as metaphase in mitosis, except homologous Paris of chromosomes assemble along metaphase plate instead of individual chromosomes
- orientation of each homologous pair on metaphase plate = random + independent of any other homologous pair
- maternal / paternal chromosomes can end up facing either pole = called independent assortment, so can result in many diff combinations of alleles facing poles
- independent assortment of chromosomes in Metaphase 1 results in genetic variation.


Describe the Anaphase 1 stage of Meiosis 1.🌟

- diff from anaphase of mitosis as homologous chromosomes are pulled to opposite poles + chromatids stay joined together
- sections of DNA on entangled 'sister' chromatids now break off + rejoin, which can cause an exchange of DNA
- points at which chromatids break + rejoin = chiasmata
- when exchange occurs, recombinant chromatids form, genes exchanged between chromatids
- genes exchanged may be diff alleles of same gene, so combination" of alleles on recombinant chromatids will be diff from allele combination on either of original chromatids
- this new combination of alleles makes genetic variation, sister chromatids are no longer identical


Describe the Telophase 1 stage of Meiosis 1.🌟

- essentially same as in mitosis, chromosomes assemble at each pole + nuclear membrane reforms, chromosomes uncoil
- cell undergoes cytokinesis + divides into 2 cells
- reduction of chromosome number from diploid to haploid is complete


Describe the Prophase 2 stage of Meiosis 2.🌟

- chromosomes that still consist of two chromatids condense + become visible again
- nuclear envelope breaks down + spindle formation begins


Describe the Metaphase 2 stage of Meiosis 2.🌟

- differs from metaphase 1, as individual chromosomes assemble on metaphase plate, as in metaphase in mitosis
- due to crossing over, chromatids no longer identical so there is independent assortment again + more genetic variation produced in metaphase 2


Describe the Anaphase 2 stage of Meiosis 2.🌟

- unlike anaphase 1, 2 results in chromatids of individual chromosomes being pulled to opposite poles after division of centromeres - same as anaphase of mitosis.


Describe the Telophase 2 stage of Meiosis 2.🌟

- chromatids assemble at poles (as in mitosis telophase)
- chromatids uncoil + form chromatin again
- nuclear envelope reforms + nucleolus becomes visible
- cytokinesis results in division of cells forming 4 daughter cells in total, which will be haploid, due to reduction division, + will aslo be genetically diff from each other + from parent cell, due to crossing over + independent assortment


Describe the specialised animal cell Erythrocytes, their role and how they are fit for this function.🌟

Produced: in bone marrow (soft, highly cellular tissue)

Role: transport O2 around body to respiring cells + carry CO2 from respiring cells to lungs for ventilation

How they are fit for their function:
-biconcave shape increases SA:V ratio of cell
- no nucleus / organelles = more space in cell for haemoglobin so each cell can carry more O2
- flexible so able to squeeze through narrow capillaries


Describe the specialised animal tissue Ciliated Epithelium.🌟

- made up of Ciliated epithelial cells that have a hair like structure called cilia on their surface
- these beat to move particles away from cells to prevent build of particles in areas that would cause infection
- contains goblet cells that secrete mucus to trap unwanted particles


Describe the specialised animal tissue Squamous Epithelium.🌟

- made up of specialised squamous epithelial cells
- made up of thin, flat cells bound tightly together + is only one cell thick
- this allows diffusion to occur at faster rate due to short diffusion distance
- is present when rapid diffusion across a surface is essential


Describe the specialised animal cell Neutrophils, their role and how they are fit for this function.🌟

Produced: by stem cells in bone marrow

- kill microorganisms w/ antimicrobial effectors
- are first cells to migrate to site of infection
- keep things under control until immune system kicks in
- destroy foreign bodies by engulfing them (phagocytosis) and secreting enzymes

How they are fit for their function:
- multi-lobed nucleus allows easier squeezing through gaps to get to infection site
- granular cytoplasm has lysosomes containing enzymes to attack pathogens
- attracted to side of infection by chemical messengers


Describe the specialised animal cell Spermatozoa (sperm cells), their role and their structure.🌟

Produced: in male sex organs (testes) in the seminiferous tubules

- are the male gametes responsible for delivering genetic information to female gamete (egg cell), in fertilisation

- tail (flagellum) allows movement
- have mitochondria in mid piece supplying them w/ energy to swim
- head contains haploid nucleus = important when gametes fuse, forming a diploid nucleus in zygote
- acrosome on head has digestive enzymes released to digest protective layers around ovum + allow penetration for sperm, leading to fertilisation