Cell structure

chapter 2

describe the function of the nucleus

• contains coded genetic info- in the form of DNA molecules

• directs the synthesis of all proteins required by the cell

• controls metabolic activities

• DNA associations with histones to form chromatin→ coils and condenses to form chromasomes

describe the structure of the nucleus

• DNA contained within the nuclear envelope (double membrane)

• nuclear envelope contains nuclear pores- allows molecules in and out

• DNA is too big to leave through nuclear pores for protein synthesis- so it is transcribe into smaller RNA molecules

what is the function of the nucleolus

• responsible for producing ribosomes

• composed of protein and RNA 

• RNA is used to produced ribosomal RNA (rRNA) then combines with proteins to form ribosomes

describe the function of mitocondria

• site for final stages of respiration

• energy stored in bonds of organic molecules is made available for cell to use to produce ATP 

• no. mitocondria in a cell is a reflection of how much energy it uses

describe the structure of mitocondria

• double membrane

• fluid interior= matrix

• membranes forming cristae contains enzymes used for aerobic respiration

• contains a small amount of DNA (mtDNA)

• can produce own enzymes and reproduce themselves

what is the function and structure of vesicles

• membranous sacs- single membrane with fluid inside

• storage and transport roles- used to transport materials inside of cells

what is the function and structure of lysosomes

• speciallised forms of vesicles that contain hydrolytic enzymes

• responsible for breaking down waste materials in cells 

• important role in the immune system→ breaks down pathogens ingested by phagocytic cells 

• role in apoptosis (cell death) 

what is the cytoskeleton?

• present in cytoplasm of all Eukaryotic cells

• network of fibres- needed for shape and stability of cells 

• organelles held in place by cytoskeleton 

• composed of microfilaments, microtubules, and intermediate fibres

describe microfilaments

• contractile fibres- form from protein actin

• responsible for cell movement + cell contraction in cytokinesis

describe intermediate fibres

gives mechanical strength to cells and helps them maintain integrity 

describe microtubules

• globular tubulin proteins polymerise to form tubes used to determine shape of cell 

• act as tracks for movement of organelles 

• spindle fibres are composed of microtubules

describe centrioles

• composed of microtubules

• plays a role in positioning flagella+ cilia

describe the endoplasmic rectillium

• network of cisternae

• connected to outer membrane of the nucleus 

describe the smooth ER

responsible for lipid and carbohydrate synthesis and storage

describe the rough ER

has ribosomes bound to the surface, responsible for synthesis and transport of protein

describe ribosomes

• can be free floating in cytoplasm or attached to the rough ER

• constructed of RNA molecules

• site of protein synthesis

describe the golgi apparatus 

• similar to structure of smooth ER 

• formed of cisternae- doesnt contain ribosomes

• modifyes proteins and packs them into vesicles

• secretory vesicles or lysosomes

describe cellulose cell walls 

• freely permeable 

• gives the cell shape- contents of cell press up against wall

• cell wall acts as defense mechanism against invading pathogens

describe vacuoles

• membrane lines sacs

• plant cells have permenant vacuoles

• membrane of vacuole= tonoplast 

• selectively permeable 

describe chloroplasts

• responsible for photosynthesis 

• double membrane structure 

• fluid enclosed= stroma 

• light dependant reactions take place in photosynthesis 

• able to make own proteins 

what are the functions of the cytoskeleton?

• establishes cell shape

• provides mechanical strength 

• movement

• chromosome separation in mitosis and meiosis 

describe microtubules

• 25nm in diameter

• globular tubulin proteins polymerise to form tubes 

• involved in the transport of organelles

describe microfilaments

• 7nm in diameter

• contractible fibres formed from the protein actin 

• responsible for cell movement and cell contraction in cytokinesis 

describe the structure of undulipodia and cilia

• cylinder of 9 pairs of microtubules in a circle and 2 in the middle 

• 9+2 arrangement

what is the function of undulipodia and cilia

• move liquid past the surface of the cell 

• enables them to swim 

describe flagella

• only present in bacterial cells 

• structurally different to undulipodia

• made of a spiral of flagellin protein attached by a hook to a protein disk that can rotate

describe division of labour 

• each organelle in a cell is speciallised to carry out a specific role

what is the first step of protein synthesis

• nucleolus produces ribosomes and mRNA 

what is the second step of protein synthesis

• mRNA and ribosomes leave through nuclear pores

what is the third step of protein synthesis

• ribosomes bind to ER

• mRNA travels to the roughER 

• ribosomes that synthesis the proteins mRNA codes for 

what is the fourth step of protein synthesis

• proteins passed into cisternae and packaged into transport vesicles

• vesicles then move towards the golgi apparatus 

what is the fifth step of protein synthesis

• vesicles fuse with cis face of golgi apparatus- modification of proteins occur 

• vesciles leave from trans face

describe prokaryotic cells

• no membrane bound organelles 

• 1-10 micrometers

• divide by binary fission 

• unicellular 

• genetic material= single looped chromosome

what happened in 1600-1800 with microscopes

• lenses were developed

• light microscopes became available

what did Robert Hooke do

• used microscope to observe a cork

• saw that the cork was made of cells

What did schleiden do

suggested all plants are made of cells

what did Schwann do

• proposed all animals are made of cells

what is the cell theory

• all living things consist of cells 

• new cells are formed only by the division of pre existing cells 

• cells contain DNA that acts as instructions for growth

what is a temporary mount

a specimen that will only last a few hours to be seen under a microscope

what is a permenant specimen

• prepared by dehydrating the specimen

• fixed in wax→ then thinly sliced

what is a dry mount

• solid specimens are viewed whole or cut into very thin slices

• placed on slide+ covered with a coverslip

what is a wet mount

• specimens suspended in liquid 

• coverslip placed on an angle to avoid airbubbles

what is a squash slide

• wet mount prepared and coverslip pressed on 

• or sample squashed between 2 slides

what is a smear slide

• edge of slide used to smear a sample along another 

• coverslip placed on top

how do you make a biological drawing from a microscope slide

• pencil 

• continuous lines

• rules label lines

• add a title

• add magnification and scale

why are stains used

• stains increase the contrast of the different components within a cell 

• contrast allows different components to be visable and identified

describe crystal violent and methalene blue

• positively charged and so it is attracted to negatively charged materials in cytoplasm 

• leads to staining of cell components

describe nigrosin and congo red

• negatively charged- repelled by cytosol

• dyes stay outside of cell leaving cells unstained 

• negative stain technique 

what is differential staining

• can distinguish between 2 types of organisms 

• can also differentiate between different organelles of a single organism

what is the Gram stain technique

• separates bacteria into 2 groups (gram+ and gram-) 

• crystal violet applied and then iodine

• slide washed w. alcohol

• gram+ retains stain (blue/purple) 

• gram- lose stain 

what is the acid fast technique

• differentiate mycobacterium from other bacteria 

• lipid solvent carry dye into cells 

• cells washed with dilute acid alcohol solution

• mycobacterium not affected (bright red)

• other bacteria loses stain (blue)

describe the fixing stage of slide preparation

chemicals used to preserve specimens in a near natural state

describe the sectioning stage of slide prep

• specimens dehydrated with alcohols and placed in a mould with wax or resin

• then thinly sliced

describe the mounting stage of slide prep

specimens secured to a microscope slide and coverslip placed on top

what is magnification

number of times larger the image is compared to the real size

what is resolution

ability to distinguish between two separate points

what are the different types of electron microscopes

• transmission electron microscope (TEM)

• scanning electron microscope (SEM)

describe TEM’s 

• beam of electrons pass through the specimen and are focused

• 2D images produced

describe SEM’s

• scans the surface and electrons are reflected to make up an image 

• 3D images

what are the disadvantages of electron microscopes

• black and white images

• specimen must be in a vacuum

• specimen must be dehydrated and therefore dead

• very expensive and large 

what is a squash slide

• wet mount prepared and a coverslip pressed on or squashed between 2 slides

what is an eyepiece graticule

• a small ruler that can be inserted into the eyepiece of a microscope

• the scale is arbitrary and therefore one unit represents different lengths depending on the objected lense used 

• must be calibrated

how do you calibrate an eyepiece graticule

• superimpose the two scales

• match up two points 

• count the number of epg divisions

• count the number of micrometer divisions

• division the micrometer divisions by the EPGU’s to find the conversion number