Topic 1: Cell Biology Flashcards
Explain passive transport and active transport across membranes. [8]
- diffusion and osmosis are passive
- do not require ATP
- diffusion from high to low conc
- facilitated diffusion uses carrier proteins
- osmosis is water movement from high to low water potential
- across a partially permeable membrane
- active transport requires energy
- energy in ATP form
- from low to high conc
- requires protein pumps
List two processes that involve mitosis. [2]
- growth by increasing cell number
- embryonic development
- tissue production
- asexual reproduction
List two functions of membrane proteins. [2]
- hormones
- enzymes
- cell to cell communication
- active transport
- facilitated diffusion
- carry electrons
Describe the events that occur in the four phases of mitosis in animals. [6]
prophase
- supercoiling of chromosomes
- chromosomes consist of sister chromatids
- formation of centrosomes
- nuclear membrane breaks down
metaphase
- attachment of spindle microtubules to centromeres
- chromosomes on the metaphase plate
anaphase
- the parting of (sister) chromatids
- the movement of sister chromatids to opposite poles
telophase
- re-formation of nuclear membranes
Describe how Pasteur’s experiments provided convincing evidence to falsify the concept of spontaneous generation. [3]
- spontaneous generation is life appearing from nothing
- broth/culture medium placed in flasks
- broth boiled/sterilized to kill microbes
- no clouding/signs of bacterial growth appeared in flasks of boiled broth
- after the necks of flasks were snapped boiled broth became cloudy/growth of microbes
- microbes from the air contaminated the broth
- curved necks allowed indirect exposure to air but prevented the entry of microbes
Discuss the advantages and disadvantages of the use of adult stem cells. [3]
Advantages
- the ability to differentiate
- repairs tissues
- fewer ethical concerns than embryonic stem cells
- adults can give consent
- adult source not killed
- no rejection problems
- less chance of cancer
Disadvantages
- difficult to find in the adult body
- differentiate into fewer cell types than embryonic stem cells
Cells go through a repeating cycle of events in growth regions such as plant root tips and animal embryos. Outline this cell cycle. [4]
- mitosis is the division of a nucleus to produce two genetically identical daughter cells
- PMAT
- cytokinesis after mitosis
- interphase is the metabolically active phase between cell divisions
- interphase consists of S, G1, G2
- DNA replicates in S phase
- cell growth
Describe the origin of eukaryotic cells according to the endosymbiotic theory. [4]
- chloroplast and mitochondria were once free-living organisms
- larger cell took in other cells (chloroplast/mitochondria) by endocytosis (engulfing)
- symbiotic relationship: did not digest cell, kept the cell alive
evidence for endosymbiosis
- DNA loop
- double membrane
- 70s ribosomes
Outline the cell theory. [2]
- living things are composed of cells
- cells are the smallest unit of life
- cells come from pre-existing cells
State the functions of the following organelles of a eukaryotic animal cell: lysosome, Golgi apparatus, free ribosomes, plasma membrane, rough endoplasmic reticulum. [5]
- lysosome: has digestive enzymes to break down food
- golgi apparatus: processes and packages proteins
- free ribosomes: site of protein synthesis
- plasma membrane: controls entry and exit of materials
- rough endoplasmic reticulum: synthesis and transport of proteins between organelles
Describe the characteristics of stem cells that make them potentially useful in medicine. [5]
- undifferentiated
- retain the capacity to divide
- produce cell cultures
- repair damaged cells
- specialize in different ways (pluripotent/totipotent)
- forms a different variety of tissues
- used in medical research
Explain the importance of surface area to volume ratio as a factor limiting cell size. [7]
- volume increases, SA to volume ratio decreases
- oxygen enters through cell surface
- wastes leave through cell surface
- rate of substance crossing depends on surface area
- larger cell requires more metabolic activity (requires more food and oxygen)
- larger volume means longer diffusion time
- more waste produced
- excess heat cannot be lost efficiently
- eventually SA cannot serve requirements of the cell
- critical ratio stimulates mitosis
- thus size of cell is reduced and kept within size limits
Outline, with an example, the process of exocytosis. [5]
- vesicles carry material to plasma membrane
- vesicle fuses with membrane
- joining of phospholipid bilayers
- aided by fluidity of membrane
- material expelled from cell
- membrane flattens
- e.g. exocytosis of neurotransmitter
Discuss alternative models of membrane structure including evidence for or against each model. [8]
- early evidence showed membranes are partially permeable
- organic solvents penetrate faster than water, suggesting non-polar regions
- chemical analysis showed membrane mostly consisted of proteins and lipids
- layer of phospholipids spread over water, orientated into monolayer with hydrophobic tails out of water, hydrophilic heads in water surface
- Davson-Danielli model proposed phospholipid bilayer coated with protein molecules on both surfaces
- supported by evidence from electron microscopy
- three-layered structure
- model cannot account for hydrophobic proteins
- used freeze fracturing later
- led to fluid mosaic model of protein molecules floating in fluid lipid bilayer
- particles project partially and right through lipid bilayer
- peripheral and integral proteins present
Explain how the cell cycle is controlled. [4]
- cell cycle is a sequence of stages (G1, S, G2, mitosis)
- controlled by cyclins
- levels of cyclin fluctuates
- conditions inside and outside affect regulation
- cyclins bind to cyclin-dependent kinases and activates them
- kinases phosphorylate other proteins
- phosphorylated proteins perform specific functions in the cell cycle
four cyclins acting at different phases
- cyclin D: triggers cells to move from G0 to G1 and from G1 to S
- cyclin E: prepares the cell for DNA replication in S
- cyclin A: activates DNA replication inside the nucleus in S phase
- cyclin B: promotes assembly of mitotic spindle and other tasks in the cytoplasm to prepare for mitosis
