Membranes And Cell Divisions Flashcards
What are the roles of the membranes within cells and at the surface
- partially permeable barriers between the cell and its environment, between organelles and the cytoplasm and within organelles
- sites of chemical reactions
- sites of cell communication (cell signalling). Release chemicals
- contain receptors for these chemical signals
- regulates transport of materials in and out of the cell
- may contain enzymes involved in specific metabolic pathways
- have antigens so the organisms immune system can recognise the cell as being self and not attack it
How can molecules pass through a partially permeable membrane
- very small molecules simply diffuse through the cell membrane
- some substances dissolve in the lipid bilayer and pass through
- other substances pass through special protein channels or are carried by carrier proteins
Who developed the fluid mosaic model and when
- singer and nicolson
- 1972
What is the fluid mosaic model
Theory of cell membrane structure with proteins embedded in a sea of phospholipids
Why is the plasma membrane fluid
Phospholipids and proteins are free to move
Why is the plasma membrane a mosaic
Proteins are randomly arranged
What is a glycolipid
Phospholipid with a chain of carbohydrate molecules attached
What is a glycoprotein
Protein with a chain of carbohydrate molecules attached
What are the different components of the plasma membrane
- phospholipid : hydrophobic phosphate head, hydrophilic fatty acid tail
- glycoprotein
- proteins: channel, carrier, intrinsic, extrinsic
- olygocarbohydrate
- glycolipid
- cholesterol
What are the different types of proteins in the plasma membrane
Channel proteins - contain pores to allow ions with electrical charges to pass through
Carrier proteins - change their shape to carry specific molecules across the membrane
Other proteins can attach to carrier proteins and act as enzyme, receptor or antigen sites for complementary-shaped signalling chemicals
How thick is a cell surface membrane
5-10 nm
What factors effect membrane permeability
Temperature - effects KE. Chance of collisions happening
Solvent concentration
What is diffusion
The net movement of molecules from an area of high concentration to low concentration across a partially permeable membrane
Does not require ATP
What is facilitated diffusion
Movement of molecules from an area of high concentration to low concentration across a partially permeable membrane via protein channels or carriers.
Does not require ATP
What affects the rate of diffusion
- temperature
- diffusion distance
- surface area
- size of diffusing molecule
- concentration gradient
What is osmosis
The movement of water molecules across a partially permeable membrane down their water potential gradient
What is water potential
Mesure of the tendency of water molecules to diffuse from one region to another
What has the highest water potential
Pure water = 0
Osmosis in animal cells
- lysis
- normal
- crenated
What does it mean when an animal cells is in lysis
- higher water potential: more water coming into cell then out
- lower concentration
Cell will burst
What does it mean if an animal cell is crenated
- low water potential: more water leaving then coming in
- high concentration
Cell will shrivel
Osmosis in plant cells
- turgid
- normal
- flaccid
what does it mean if a plant cell is turgid
- high water potential: more water in than out
- lower concentration
Cell will burst
what does it mean if a plant cell is flaccid
- lower water potential: more water leaving than entering
- higher concentration
Cell will shrivel
What does it mean if a solution is hypertonic
More water leaves the cell
What does it mean if a solution if hypotonic
More water enters the cell
What does it mean if a solution is isotonic
Dynamic equilibrium
What is a glycoprotein
A carbohydrate chain attached to a protein molecule
Features of a carbohydrate molecule (oligosaccharide)
- very hydrophilic
- attract water with dissolved solutes
- helps the cell interact with its watery environment and obtain dissolved substances
What is the function of cholesterol in the plasma membrane
Mechanical stability and flexibility
What are the main functions of membrane proteins
- transport
- receptors
- anchorage
- cell recognition
- intracellular joining
- enzyme activity
What are the different types of cell transport
- active
- passive
Examples of passive transport
- simple/lipid diffusion
- facilitated diffusion
- osmosis
Examples of active transport
- active transport
- bulk transport
What is an active method of transport
Requires ATP produced during cellular respiration
What is passive method transport
- takes place as a result of concentration, pressure or electrochemical gradients.
- it involves no metabolic energy from the cell
What particles can pass through the plasma membrane
- gases (oxygen, carbon dioxide)
- hydrophobic molecules (benzine)
- small polar molecules (water, ethanol)
What particles can’t pass through the plasma membrane
- large polar molecules (glucose)
- charged molecules (ions, amino acids)
What is Fick’s law
Rate of diffusion is proportionally identical to (surface area x concentration gradient) / diffusion distance
What is bulk transport
Large macromolecules, like proteins and polysaccharides and even smaller cells, are transported by bulk transport using membrane vesicles
What is the word for into in bulk transport
Endo
What is the word for out in bulk transport
Exo
What is the word for liquids in bulk transport
Pino
what is the word for solids in bulk transport
Phago
What is endophagocytosis
Moving solids into a cell
What is a phosopholipid bilayer
The two layers of phospholipids arranges in such a way that the your hydrophobic fatty acid tails are facing inwards and their hydrophilic polar heads are facing outwards
What does the cell theory state
- new cells are always formed by division of old cells
- the life of a cell from one division to the next is called the cell cycle
What are the three main phases of the cell cycle
- interphase
- mitosis
- cytokinesis
What happens during each stage of interphase
G1 - organelles replicate, cell size increases, protein synthesis
S - DNA replication occurs
G2 - spindle proteins synthesised
What are the different stages of mitosis
- prophase
- metaphase
- anaphase
- telophase
What happens in prophase
- the chromosomes that have been replicated in S phase of interphase and consists of two identical sister chromatids shorten and thicken as the DNA supercoils
- nuclear envelope breaks down
- tubulin treads form
What happens in metaphase
- the pairs of chromatids attach to the spindle threads at the equator region
- they attach by their centromeres
What happens in anaphase
- the centromere of each pair of chromatids splits
- motor proteins pull each sister chromatids of a pair in opposite directions towards opposite poles
- the chromatids now called chromosomes form a V shape
What happens in telophase
- the separated chromosomes reach the poles
- new nuclear enveloped forms around each set of chromosomes
- cell now contains two nuclei each genetically identical to each other
what happens in cytokineses
The cell splits to form two identical daughter cells
What is the formula for mitotic index
Cells in mitosis / total number of cells
What are the functions of meiosis
- form haploid gametes
- half chromosome number: sexual lifecycle
- introduce genetic variation
Where does meiosis take place
In the reproductive organs of both male (plants) and females (animals)
what is the product of meiosis
4 genetically varied daughter cells
- containing half the number of chromosomes
- haploid
- called gametes
What is a homologous chromosome
Structural unit consisting of a long thread of coiled DNA and protein. Same structure. One maternal and one paternal
What is a sister chromatid
Duplicated chromosomes attached by a centromere
What is a bivalent
Connected homologous chromosomes, forming a unit of 4 DNA molecules, essential for the equilibrium segregation of the chromosome pool
What happens in prophase 1
- chromatin condenses and each chromosome supercoils
- nuclear envelope breaks down
- spindle threads of tubulin proteins form from the centriole in animal cells
- the chromosomes come together in their homologous pairs
- crossing over occurs
what is crossing over
Where non-sister chromatids wrap around each other and may swap sections so that alleles are shuffled
- creates a new combination of alleles
What happens in metaphase 1
- pairs of homologous chromosomes attach along the equator of the spindle
- each attach to a spindle thread by its centromere
- homologous pairs are arranged randomly
- arrange in independent assortment
What is independent assortment
- homologous chromosomes line up randomly in metaphase 1
- sister chromatids in metaphase 2
- new combination of maternal and paternal chromosomes
What happens in anaphase 1
- members of each pair of homologous chromosomes are pulled apart by motor proteins that drag them along the tubulin threads of the spindle
- centromeres do not divide
- each chromosome consists of two chromatids
- crossed over areas separate from each other, resulting in swapped areas of chromosomes and allele shuffling
What happens in telophase 1
- two new nuclear envelopes form around each set of chromosomes and the cell divides by cytokinesis
- each new nucleus contains half the original number of chromosomes
- each chromosome consists of two chromatids
What happens in prophase 2
- nuclear envelope breaks down
- chromosomes condense each containing two chromatids
- chromatids of each chromosomes are no longer identical
- spindles form
What happens in metaphase 2
- chromosomes attach, by their centromere, to the equator of the spindle
- chromatids of each chromosome are randomly arranged
What happens in anaphase 2
- centromeres divide
- chromatid from each chromosome are pulled apart by motor proteins
- pulled along the tubulin of the spindle to each pole
- chromatids are randomly segregated
What happens in telophase 2
- nuclear envelope forms around each of the four haploid nuclei
How does meiosis cause genetic variation
- crossing over
- independent assortment
- random fertilisation
What is the importance of genetic diversity
- gives the organism a better chance of survival
- evolution
What causes genetic diversity
Genetic mutation
