module 2 Flashcards
(22 cards)
roles of membranes
partially permeable barriers between the cell
and its environment, between organelles and
the cytoplasm and within organelles
sites of chemical reactions
cell signalling
What factors affect membrane fluidity?
Temperature
Solvent conc.
How does temperature affect membrane fluidity?
Cold:
Fatty acids become compressed- less fluidity. More unsaturated FA, more fluid.
Hot:
Increased fluidity. Phospholipids more Ek so move around more.
Permeability increases.
What may be affected if permeability of membrane increases?
- Intrinsic proteins may shift. Intrinsic enzymes may be impacted therefore their reactions too.
- Infolding of plasma membrane during phagocytosis
- Cell signialing by releasing chemicals
What are the events that occur in interphase?
G1, S, G2
What occurs in G1?
- Cells grow and increase in size
- Genes transcribed to make RNA
- Organelles duplicate
- Protein synthesis (making enzymes for DNA replication)
What occurs in the S phase?
- DNA replicates
- All chromosomes duplicate -> sister chromatids
- DNA bases become more susceptible to mutagenic agents so more likely to mutate.
What happens in G0?
Cells may undergo apoptosis, senescence or differentiation.
What happens in the M phase?
- Cell growth stops
- Nuclear division
- Cytokonesis
What is the purpose of checkpoints in cell division?
- Prevents uncontrolled cancerous growths
- Detect and repair damage to DNA
Why is it important that the cell cycle happens in a specific sequence?
- Cycle cannot be reversed
- DNA is only duplicated once during each cell cycle
Role of mitosis?
- Growth
- Tissue repair
- Asexual reproduction
Steps of Mitosis?
Prophase:
- Nuclear envelope breaks down
- DNA supercoils
- Chromosomes condense and duplicate -> chromatids.
Metaphase:
- Sister chromatids align along equator of cell
- Sarcomeres form spindle fibres that attach to centromeres of chromosomes
Anaphase:
- Chromosomes split at chiasmata into chromatid. Each chromatid pulled to either pole by spindle fibres at centromere
Telophase:
- Nuclear membrane reforms
- Chromatids decondense -> chromosomes
- Nuclear envelope forms
Cytokinesis:
- In animals, membrane pinches in at top and bottom to separate cells
- In plants: end plate forms between two cells
Significance of meiosis?
- Creates haploid cells
- Genetic variation
Process of Meiosis?
Prophase I:
- Nuclear envelope breaks down
- DNA supercoils
- Chromosomes condense and form sister chromatid pairs
- Homologous pairs of chromosomes (same gene loci) match up and undergo crossing over
Metaphase I:
- Homologous pairs of chromosomes align along equator
- Cytoskeleton forms spindle fibres attached to sarcomere
- Spindle fibres attach to centromere of chromosome pairs
Anaphase I:
- Homologous pairs are split by spindle fibres, each pair of sister chromatids pulled to one pole
Telophase I:
- chromatids decondense
- nuclear envelopes forms again
- temporary rest
Prophase II:
- chromatids recondense
Metaphase II:
- chromatids align along equator
- Spindle fibres attach to centromeres of sister chromatids
Anaphase II:
- Sister chromatids pulled to either pole via centromeres
Telophase II:
- Nuclear envelope reforms
Adaptation of erythrocytes?
Small so large SA:V
Flexible to fit through narrow capillaries
No nucleus, mitochondria or endoplasmic reticulum- more space for Hb
Adaptation of sperm?
Digestive enzymes (acrosomes) in tip to digest protective layer of ovum
Lots of mitochondria for respiration
Tail
Adaptation of palisade cells?
- long and cylindrical cells
- large vacuole so chloroplasts positioned to top of cell, reducing diffusion pathway for CO2
- many chloroplasts
- cytoskeleton threads to move chloroplasts closer to the surface at low light intensity
How do guard cells work?
- ATP a.t K+ ions from surrounding cells into guard cells
- Lowers water potential of guard cell
- Water enters the cells by osmosis
- Guard cells swell, tips bulge so stomata enlarges.
- As stomata enlarge air can enter the layer beneath the palisade.
- CO2 diffuse into palisade cells for photosynthesis and keep conc. gradient
- O2 diffuse out
Adaptation of root hair cells?
Hair-like projections increase SA for adsorption
Mineral ions AT to lower water potential via carrier proteins
What kind of stem cells are embryonic stem cells?
Pluripotent
Can differentiate into any cell type except for placental tissue
What is a totipotent stem cell?
Stem cells that are present right at the start of embryonic development that can differentiate into literally anything
