cell structure and division Flashcards
function of cell surface membrane
partially permeable;
physical barrier;
recognition;
transport
structure of cell surface membrane
found on the surface of animal cells, inside the cell wall of plant cells; made mostly of phospholipids and proteins
function of nucleus
stores genetic info for protein (polypeptide) production; controls cells’ activities by controlling the transcription of DNA (makes instructions to make proteins); pores allow substances to move between the nucleus and the cytoplasm; nucleolus makes ribosomes and pRNA; where DNA replication occurs
structure of nucleus
large organelle surrounded by a double membrane nuclear envelope, which contains many pores;
nucleus contains chromosomes (made from protein-bound linear DNA); and a nucleolus
structure+function of nuclear envelope
double-membrane surrounding the nucleus, which controls exit and entry of materials
function of mitochondria
site of aerobic respiration; where ATP is produced; releases energy
structure of mitochondria
oval-shaped with a double membrane, inner membrane is folded to form cristae;
inside the cristae is the matrix which contains the enzymes involved in respiration
structure+function of cristae
folds in the inner membrane of the mitochondria; they are the site of oxidative phosphorylation
function of golgi apparatus
processes and packages new lipids and proteins; makes lysosomes
structure of golgi apparatus
fluid-filled, membrane-bound flattened sacs; vesicles are found at the edges
4 functions of golgi apparatus
- produces secretory enzymes and carbohydrates
- stores and modifies proteins & triglycerides
- forms vesicles for transporting proteins and triglycerides
- forms lysosomes
function of vesicles
stores lipids and proteins made by the golgi apparatus and transports them out of the cell via the cell-surface membrane
structure of vesicles
small fluid-filled sac in the cytoplasm, surrounded by a membrane; produced by the golgi apparatus
function of ribosomes
site of protein synthesis
structure of ribosomes
small organelle, floats freely in the cytoplasm, or is attached to the rough endoplasmic reticulum; made of proteins and RNA; not surrounded by a membrane
function of rough endoplasmic reticulum
folds and processes proteins+glycoproteins that have been made at the ribosomes
structure of rough endoplasmic reticulum
system of membranes enclosing a fluid-filled space; covered in ribosomes
how does the structure of the rough endoplasmic reticulum help enable synthesis of proteins?
the rough endoplasmic reticulum has ribosomes and a large surface area
function of smooth endoplasmic reticulum
synthesises and processes lipids;
site of synthesis , storage and transportation of lipids and carbohydrates.
structure of smooth endoplasmic reticulum
system of membranes enclosing a fluid-filled space; no ribosomes
function of lysosomes (animal only)
contains digestive/hydrolytic enzymes (lysozymes) surrounded by membrane;
used to digest invading cells or break down worn components of the cell
structure of lysosomes (animal only)
round membrane-bound organelle; type of golgi vesicle
function of chloroplasts (plant only)
site of photosynthesis;
some in grana others in stroma
structure of chloroplasts (plant only)
small, flattened structure found in plant and algal cells;
surrounded by a double membrane;
has thylakoid membranes which are stacked up to form grana and stroma
what are grana?
stacks of thylakoids found in the chloroplast.
what are thylakoids?
flattened sacs in the chloroplast, containing chlorophyll;
site of the light-dependent reaction for photosynthesis
what is the stroma?
the matrix of the chloroplast in a plant cell;
site of the light-independent reaction for photosynthesis
function of cell wall (plants and prokaryotic cells)
provides rigidity or integrity to the cell and stops the cell from bursting by exerting inward pressure to prevent osmosis;
this enables turgidity which makes parts of the plant semi-rigid
structure of cell wall (plants and prokaryotic cells)
rigid structure that surrounds cells in plants, algae and fungi;
made of cellulose in plants and algae, made of chitin in fungi, made of murein in prokaryotic cells
function of vacuole (plants only)
helps maintain pressure in the plant, keeps it turgid;
stops plant wilting;
stores sugars and amino acids which can act as a temporary food storage;
in petal cells, it can store pigments to attract pollinating insects.
structure of vacuole (plants only)
membrane-bound organelle found in cytoplasm;
contains cell sap (weak solution of sugar and salts);
surrounding (single) membrane is called the tonoplast
function of plasmids (prokaryotic cells)
contains genes for antibiotic resistance;
acts as a vector;
can be passed between prokaryotic cells via pilli (short hairs)
structure of plasmids (prokaryotic cells)
small loop of DNA; amounts vary in each cell
function of circular DNA (prokaryotic cells)
controls cell’s activities (transcription of proteins)
structure of circular DNA (prokaryotic cells)
one long, coiled up strand that floats free in the cytoplasm; not attached to histones
function of flagellum (prokaryotic cells)
rotates to make cell move (not present in all prokaryotic cells)
structure of flagellum (prokaryotic cells)
hair-like structure; made of flagellin
function of capsule (prokaryotic cells)
protects bacteria from attack by immune system
structure of capsule (prokaryotic cells)
made of secreted slime
Describe viral replication [3 marks]
attachment proteins attach to receptors;
viral/nucleic acid enters cell and replicates in the cell;
cell produces viral protein;
virus assembled and released
Describe binary fission [3 marks]
replication of circular DNA and plasmids;
cell enlarges and DNA moves to opposite poles;
division of cytoplasm;
2 daughter cells produced
how to calculate magnification
I=AM
optical microscopes
uses light to look at cells and larger organelles;
stained to provide contrast;
prep is simple and quick;
natural colour of living tissues can be observed;
only magnifies up to x1500;
resolution is restricted to 0.2(micrometers) so cannot view smaller organelles due to longer wavelengths of light
2 types of electron microscopes
scanning (SEM)
transmission (TEM)
electron microscopes
much higher resolution than optical microscopes (up to 0.0002 micrometers) due to the electrons having a much shorter wavelength;
magnifies x1500000;
use magnets (affected by magnetic field);
preparation is longer and more complex;
prep may distort specimen;
images are black + white;
cannot view living cells
scanning microscopes
beam of e- reflected off the surface (3d image);
whole cells, tissues and organisms can be viewed;
lower resolution than TEM
transmission microscopes
beam of electrons pass through specimen (focused by electromagnets);
specimen needs to be heavily stained (with heavy metals);
requires thinly sliced specimen;
viewed in a vacuum;
higher resolution than SEM
cell fractionation (describe)
- homogenisation–>grinding up the cells in a blender
CONDITIONS:
>ice cold
>isotonic (solution has same water potential as cells)
>have a buffer added - filtration (through a gauze)
- ultracentrifugation–>separate organelles by mass-density
>filtered solution centrifuged at low speed
>respin supernatant at higher speed
> process repeated at higher speeds
cell fractionation (explain)
- homogenisation–> break opens the cells, breaking up the plasma membrane to release the organelles
> ice cold: reduces enzyme activity, preventing organelles from being broken down
> isotonic solution: prevents damage to organelles by osmosis (prevents organelle lysis)
>have a buffer added: maintain pH of a solution to prevent proteins denaturing - filtration–>take out debris e.g. connective tissue and whole cells
- ultracentrifugation
>centrifuge at low speed–separate out heaviest organelles e.g. nuclei
>respin at higher speed– remove heaviest organelles from supernatant e.g. chloroplast into the pellet
>process repeated at higher speeds–to remove the heaviest organelles in pellets each time
cell cycle
G1, synthesis, growth 2 [interphase] and mitosis
G1>growth 1
cell gets bigger;
volume and mass increases (more organelles);
mitochondria (needed to produce ATP and release energy to allow the spindle fibres to pull the chromosomes to opposite sides of the cell
synthesis
DNA replicates
G2>growth 2
cell keeps growing and protein synthesis increases to make spindle fibres for mitosis
mitosis
cell division;
for growth and repair;
4 stages (PMAT) and cytokinesis
prophase
chromosomes condense and become shorter and more visible;
chromosomes appear as two sister chromatids and are joined at the centromere;
centrioles move to the poles, begin to produce spindle fibres;
nuclear envelope breaks down
metaphase
chromosomes become attached to the spindle fibres at the centromere;
chromosomes line up along the equator
anaphase
the centromere splits;
sister CHROMATIDS are pulled to opposite poles of the spindle;
CHROMATIDS appear appear ‘v’ shaped
telophase (and cytokinesis)
chromatids are chromosomes again;
become long and thin;
nuclear envelope reforms;
division of cytoplasm (cytokinesis)
mitotic index
proportion of cells undergoing mitosis
mitotic index=number of cells in mitosis/total no. of cells observed x100
Describe the appearance and behaviour of chromosomes during mitosis [5 marks]
prophase: chromosomes are visible and condensed
metaphase: chromosomes line up across the equator
anaphase: centrioles break up centromere; sister CHROMATIDS are pulled to opposite poles by spindle fibres
telophase: chromatids uncoil themselves as they are surrounded by the nuclear envelope
cancer
role of cell membrane
acts as a barrier between the cell and its environment;
controls what substances enter and exit the cell;
partially permeable membrane-> allow some substances through but not others;
respond to environment-> cell surface receptors;
membranes around organelles divide the cell into compartments to stop the enzymes from leaving into the cytoplasm
membrane structure
phospholipid bilayer; hydrophilic PL head, hydrophobic fatty acid tail;
centre is hydrophobic so water-soluble substances cannot pass through
cholesterol in a cell membrane
provides stability and strength;
binds to the tails of phospholipids causing them to pack together
channel proteins in a cell membrane
form pores in the membrane;
different channel proteins facilitate different charged particles;
transport ions and polar molecules
(water-soluble; cannot diffuse through membrane because centre of bilayer is hydrophobic)
function of carrier proteins in a cell membrane
transports large molecules
1. large molecule attaches to a carrier protein
2. protein changes shape
3. releases the molecule on the opposite side
receptor proteins in the cell membrane
allow the cell to detect chemicals released by other cells (e.g. toxins)
ATP synthase
protein enzyme that catalyses ATP production
membrane folding (adaption of membrane)
increases surface area;
increase the number of carrier/channel proteins;
increases rate of diffusion
‘fluid-mosaic’ structure
phospholipid molecules form continuous, double layer;
‘fluid’ because the phospholipids are always moving;
proteins and cholesterol are scattered through the bilayer like tiles in a mosaic
diffusion
net movement of particles from an area of higher concentration to an area of lower concentration
OR
net movement of particles down its concentration gradient
*passive process
simple diffusion
diffusion that does not require the assistance of membrane proteins
facilitated diffusion
requires the assistance of membrane proteins to speed up rate of diffusion
factors that affect rate of simple diffusion
concentration gradient: the higher it is, the higher the rate of diffusion;
the thickness of exchange surface: shorter/longer diffusion pathway;
surface area; the larger the surface area, the faster the rate of diffusion
factors that affect rate of facilitated diffusion
concentration gradient: the higher the concentration gradient, the faster the rate of facilitated diffusion
number of channel or carrier proteins: when all proteins are in use, facilitated diffusion can’t happen faster
osmosis
net movement of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential
water potential
the likelihood of water particles to diffuse in or out of a solution
(pure water has highest water potential)
factors that affect the rate of osmosis
water potential gradient: the higher the water potential gradient, the faster the rate of osmosis;
thickness of the exchange surface: osmosis pathway;
surface area: the larger the surface area, the fast the rate of osmosis
active transport
the movement of substances across a cell membrane against their concentration gradient which requires energy
process of active transport
molecule attaches to carrier protein, the protein changes shape and the molecule is released on the opposite side of the membrane
what energy does active transport need?
ATP; produced by respiration
ATP goes under a hydrolysis reaction, splitting into ADP and inorganic phosphate which releases energy so solutes can be transported
co-transporters
a type of carrier protein that binds two molecules at once;
the concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient
factors affecting the rate of active transport
speed of individual carrier proteins;
number of carrier proteins;
rate of respiration and availability of ATP
