2.1-Cell structure

what is the structure and function of cell surface membrane?

structure:

membrane found on cell surface and most internal organelles

made of a phospholipid bilayer which contains embedded proteins

function:

selectively permeable

allows cell identification

what is the structure and function of the nucleus?

structure:

largest organelle

double membrane (nuclear envelope) that has pores, jelly like nucleoplasm and a dense region (nucleolus)

function:

DNA contains genetic code for making proteins

nucleolus manufactures ribosomes

site of transcription

site of DNA replication

what is the structure and function of mitochondrion?

structure:

oval shaped organelles surrounded by 2 membranes

inner membrane folded and forms cristae

fluid inside- matrix

contains DNA like that of prokaryotes (short, circular, not associated with histones)

function:

produces ATP from aerobic respiration

ATP used by cell for active processes e.g. active transport, protein synthesis

what is the structure and function of rough endoplasmic reticulum?

structure:

continuous with the outer nuclear membrane

consists of flattened sacs called cisternae

appears rough due to ribosomes attached to membranes

function:

synthesis and transport of proteins thru cytoplasm

what is the structure and function of ribosomes?

structure:

made of RNA and proteins

not surrounded by membranes

function:

protein synthesis

what is the structure and function of the smooth endoplasmic reticulum?

structure:

consists of flattened sacs called cisternae

no ribosomes attached

function:

synthesises and transports lipids and carbohydrates

what is the structure and function of the golgi body?

structure:

stack of flattened sacs, each surrounded by a membrane

vesicles are continually pinched/bud off from the ends of these sacs

function:

modifies proteins that are made in the cell

packages them into vesicles

forms lysosomes

what is the structure and function of lysosomes?

structure:

spherical sacs surrounded by a single layer of membrane

containing hydrolytic enzymes e.g. lysozomes

functions:

digest unwanted material in the cell e.g. damaged organelles or pathogens

cells in the pancreas produce enzymes. explain why these cells have large amounts of rough ER, golgi apparatus and mitochondria?

mitochrondria- produce ATP to release energy for protein synthesis

golgi apparatus- processes and packages enzymes prior to secretion

rough ER- synthesis and transport of enzymes

what is the cell wall?

made of cellulose, the wall surrounds the cell membrane and has high tensile strength

allow it to resist the force of water entering the cell by osmosis- prevents osmotic lysis

what are cell walls in fungi made of?

chitin

what is a vacuole?

filled with cell sap- a weak solution of sugars and salts

helps give the cell rigidity + maintains cell turgor

what are chloroplasts and what are the important features?

only found in plant and algal cells + site of photosynthesis

important features:

double membrane surrounding it forming an envelope

internal thylakoid membranes, stacked to form grana

chlorophyll located in thylakoid membranes + absorbs light for photosynthesis

stroma- contains enzymes needed for photosynthesis + starch grains

contains DNA like that in found in prokaryotes

what is two differences between prokaryotic and eukaryotic cells, and how do they replicate?

smaller than eukaryotic cells + don’t contain membrane-bound organelles in their cytoplasm

form new cells by binary fission

how is the DNA in prokaryotic cells?

free in the cytoplasm

circular, short

not associated with proteins

what is the cell wall in prokaryotes made of?

murein (glycoprotein)

what are the three features that MAY be present in some prokaryotes but not all?

capsule, flagella, plasmids

what is the flagellum and what does it do?

tail of the cell + thin rotating fibre

rotates to enable bacteria to move

what are plasmids and what do they do?

smalll loops of DNA which only carry a few genes + replicates independently

contains DNA for making proteins

carries genes for antibiotic resistance

what is a capsule and what does it do?

slimy layer made of protein + extra layer outside of cell wall

prevent bacteria from dessicating (drying out) + phagocytosis

protects bacteria against host’s immune system

what are the 6 differences between prokaryotic and eukaryotic cells?

1) prokaryote- no nucleus, circular DNA, not associated with protein / eukaryote- has a nucleus with linear chromosomes associated with histones

2) prokaryote- forms new cells by binary fission/ eukaryote- form new cells by mitosis and meiosis

3) prokaryote- no membrane bound organelles/ eukaryote- contains membrane bound organelles e.g. mitochondria

4) prokaryote- has a cell wall of murein/ eukaryote- plants- cellulose, fungi- chitin, found in algae

5) prokaryote- smaller ribosomes/ eukaryore- large ribosomes

6) prokaryote- MAY have a capsule, flagella and plasmids/ eukaryote- doesn’t have them

what advantage does cell specialisation provide an organism with?

cells can work more efficiently as it is specialised to perform a specific function

what is a tissue and what are some examples?

group of similar cells working together to perform a particular function

e.g. epithelial tissues and xylem tissues

what is an organ and what are some examples?

group of different tissues working together perform to particular function

e.g. leaf, stomach

what is an organ system and what are some examples?

group of different organs working together to perform a particular function

e.g. digestive, circulatory, respiratory

why are viruses described as acellular and non-living?

acellular- lack organelles e.g. cell membrane and nucleus

non-living- inability to reproduce independently/no metabolic processes

what are the only three components of viruses?

genetic material- either DNA or RNA

capsid- protein coat- encloses nucleic acid+ protects it from damage

attachment protein- allow the virus to attach to a host cell (complementary to receptors on host cell membrane)

what is magnification?

how much bigger a sample appears to be under the microscope than it is in real life

what is resolution?

minimum distance between 2 objects/points at which they can be seen as separate

what is the magnification, resolution and principles of use of optical microscope?

magnification x1500

low resolution

uses light and glass lenses

what is the magnification, resolution and principles of use of electron microscope?

x500,000 magnification

higher resolution

uses beam of electrons and electromagnets

what are the advantages of optical and electron microscope?

optical:

for cells, larger organelles and individual bacteria

simple and cheaper

colour images + living specimen can be seen

electron:

for smaller organelles e.g ribosomes and internal details in organelles e.g. cristae in mitonchondria

for 3D objects

high magnification + resolution

what are the limitations of optical and electron microscope?

optical:

low magnification + resolution

electron:

complex staining procedure

require thin specimen

B and W images

dead specimen

complex preparation can result in artefacts

what are the features of SEM?

electrons are reflected off surface of objects

thin sections don’t required

used for 3D objects

lower resolution than TEM

shows surface of object

what are the features of TEM?

beams of electrons are transmitted through specimen

specimen must be thin

used for smaller organelles

has greater resolution than SEM

shows details of internal structures to be seen

what is the equation for image size?

actual size x magnification

what are two conversions to remember?

1mm = 1000 um

1um = 1000nm

what is the order in which the organelle pellets are formed?

nucleus

(chloroplasts)

mitochondria

lysosomes

ER

ribosomes

what is the process of cell fractionation and ultracentrifugation?

cell fractionation:

cells are broken open using a homogeniser

homogenate filtered remove cell debris and whole cells

ultracentrifugation:

suspension centrifuged at low speed

mose dense organelle, forms pellet at bottom of pellet

resr of organelles suspended in supernatant

spun at higher speed

why should the solution be kept in a cold, buffered and isotonic conditions?

cold- reduce enzyme activity that might break down the organelles

buffered- maintain constant pH so that enzyme functioning + structure of organelles

isotonic- prevent organelle damage (shrinking or bursting)