BIOLOGY ALEVELS - cell structures

2.5 -2.6

division of labour

each organelle has its functions and works togather to ensure cells success e.g. manufacturing and secretion of proteins

structure found in both eukaryotes and prokaryotes

cell surface membrane

ribosomes

cytoplasm

DNA

define eukaryotes

contains membrane bound organelles and has a nucleus containing DNA

define prokaryotes

DNA is free in the cytoplasm and doesnt contain membrane bound organelles

common cell adaptation

• folded membrane or microvilli increase SA for diffusion

• many mitochondria - large amounts of ATP for active transport

• walls one cell thick to reduce the diffusion pathway

difference from eukaryotes and prokaryotes

• prokaryotes cells dont have a nucleus whereas a eukaryotes cell does

• prokaryotes cells are less than 1-2 micrometer whereas eukaryotes are 10-100 micrometer

• prokaryotes doesnt have membrane bound organelles whereas eukaryote does

• Prokaryote contains circular DNA whereas eukaryotes contains linear DNA

• Prokaryotes contains a pili whereas eukaryotes doesnt

function of flagella in bacteria

flagella is used for the movement of bacteria and locomotion

how fimbriae differs structurally and functionally from flagella

fimbraes are shorter and thinner than flagella and is used for attachement not movement like flagella

location and general composition of bacterial cell wall

made up of peptidoglycan and is based on top of the plasma membrane and underneath the slime capsule

prokaryotes - bacteria components

ribosomes (70s) cytoplasm flagellum cell wall slime capsule plasmids plasma membrane nucleoid

eukaryotes - plant cell

cell wall cell membrane vacuole nucleus nucleolus nuclear membrane chloroplast mitochondria cytoplasm lysosomes centrioles RER SER ribosomes golgi apparatus

why the lack of membrane bound organelles doesnt stop prokaryotes from making proteins

prokaryotes contains ribosomes which can carry out protein synthesis and ribosomes are not membrane bound

some antibiotics kills bacteria by disrupting the formation of peptidoglycan molecules. explain why these kill bacteria but do not affect eukaryotes

eukaryotes dont have a peptidoglycan cell wall and these antibiotics do not damage any other cell components e.g. nucleus mitochondria

microfilament

• two intertwined strands

• mobility (pseudopodia)

• has a diameter of 7 nm

• cytokinessis of cell division

• maintains cells shape

• contraction (muscles)

• Actin

microtubules

• hollow tubes

• mobility (cilia and flagella)

• move organelles

• move chromosomes (spindle)

• diameter: 25nm

• maintains cell shape

intermediate filaments

• fibres wound into thicker cables

• maintains cell shape

• anchor nucleus and organelles

• fibrous proteins e.g. keratin

• diameter: 8-12 nm

smooth endoplasmic reticulum (SER) - structure

• system of membrane enclosing a fluid filled space

• large surface area

Smooth endoplasmic reticulum (SER) - function

synthesise, store and transport lipids and carbohydrates

Rough endoplasmic reticulum (RER) - structure

• system enclosing a fluid filled space

• has ribosomes on the outer surface

• large surface area

Rough endoplasmic reticulum (RER) - function

• synthesis of proteins and glycoproteins

• provides pathway for materials to be transported throughout the cell especially proteins

nucleus, nuclear membrane and nucleolus - structure

• nuclear envelope - double membrane

• nuclear pores - allows mRNA out

• chromatin - made from proteins & DNA

• nucleoplasm - jelly like substances

• nucleolus - makes rRNA and ribosomes

nucleus, nuclear membrane and nucleolus - function

• acts as control centre for the cell by producing mRNA and hence protein synthesis

• retain for the genetic material for the cell in the form of DNA or chromosomes

• manufacture ribosomal RNA and ribsomes

golgi apparatus - structure

• Cisternae - a group of fluid filled flattened sacs

• vesicles = small hollow structure

golgi apparatus - function

• processing and packaging new lipids and proteins made by endoplasmic reticulum (often adds carbohydrates) which are then transported by vesicles

• it makes lysosomes

ribosomes - structure

• contains ribosomal RNA and proteins

• 2 sub units

• floats freely in the cytoplasm or attached to the membrane of the RER

ribosomes - function

• protein synthesis

• 80s = eukaryotes

• 70s = prokaryotes

Mitochondria - structure

• has double membrane controls entry and exit of materials

• cristae - folded extensions on the inner membrane provide large SA, for enzyme reaction

• matrix - semi rigid material containing enzymes involved in respiration

mitochondria - function

• site of aerobic respiration

• (krebs cycle and oxidative phosphorylation) to produce ATP

• they are found in large numbers in muscles and epithilial

lysosomes - structure

• double membrane

• contains enzymes such as protease and lipase

lysosomes - function

• breaks down materials ingested by phagocytes

• release enzymes to the outside of the cell to destroy material around the cell

• digest worn out organelles to reuse useful chemicals that are made up of

• completely breaks down dead cells (autolysis)

chloroplasts - structure

• contains double membrane structure

• fluid enclosed in the chloroplast = stroma

• internal network of membrane, forming flattened sacs called thykaloid

• grana joined by membranes - lamelae

• large SA

chloroplast - function

• responsible for photosynthesis

• can make own protein

• starch is produced by photosynthesis and is presented as starch grains

centrioles - structure

• composed of microtubules

• componants of cytoskeleton

• 2 associated centrioles forms centrosome

centrioles - functions

• centrosomes = involved in the assembly and organisation of the spindle fibres during cell division

flagella and cilia - structure

• flagella = whip like

• cilia = hair like

• flagella = longer than cilia

• cilia = present in greater numbers

• cilia = 2 central microtubules (black circles) with 9 pairs of microtubules arranged in a wheel

flagella and cilia - function

• flagella = enables cell motivity and sometimes sensory organelles detecting chemical changes

• cilia = mobile/stationary stationary cilia is on the surface of the cell which is important in sensory organs e.g. nose

• mobile cilia beats in rythmic pattern and creates a current which causes fluid to move in the trachea which moves the mucus along

plasma membrane - structure

made up of lipids and salts

plasma membrane - function

controls movement of substances in and out of cells

cell wall - structure

• made up of cellulose carbohydrate

• freely permeable - substances passes in and out of cells

• cell wall gives its shape

cell wall - function

• allows turgidity

• keeps the plant upright

• prevents cell from bursting

making a protein process

1. the nucleus is the site of ribosomes and mRNA manufacture (copy the protein gene)

2. ribosomes on the RER makes proteins to be secreted (free ribosomes make proteins to stay in cells)

3. The proteins are transported from RER to golgi apparatus by vesicles

4. golgi body further processess proteins (may add sugar chains)

5. vesicles contains proteins and move towards the plasma membrane

6. exocytosis

the cytoskeleton - function

1. microtubules, microfilaments and intermediate fibres helps to support the cells organelles

2. they help cell to maintain its shape

3. they transport organelles and materials within the cell (e.g. mitosis)

4. this can cause the cell to move

light microscope use

uses light rays to observe object

light microscope - advantage

• can observe living things

• does not use harsh chemical

• easy to set up and use

• cheap and portable

light microscope - disadvantage

• low magnification (up to 2000 times)

• low resolution

transmission EM - use

uses focused beams of electrons through sections of tissues

transmission EM - advantage

• very high resolution image - very detailed image or cell organelles (upto 5000000 times)

• high resolutions

• can see details inside cells

scanning EM - use

uses focused beams of electrons reflected off the tissue

scanning EM - advantage

• SEM can produce 3D images of a speciman

• high magnifaction (upto 5000000 times)

• high resolution

• can see details of the surface of the structure

transmission and scanning EM - disadvantages

• TEM can be used for thin tissues and must be performed on very thin specimen as thick specimen easily absorb the electrons and therefore do not produce good image

• expensive

• can only see dead materials

• harsh materials/chemicals used in preparation which can cause artefact

laser scanning confocal - use

uses laser beam of light to illuminate chemical stains within the specimen. these then fluoresce

laser scanning confocal - advantage

• can see living cells

• can observe cell processes by tracking molecules

• higher resolution than light microscope

laser scanning confocal - disadvantage

• more expensive than light microscope

• more complex than light microscope