B03 Cell Structure

What is the function of the cell surface membrane?

controls the entry and exit of substances

Describe the structure of the cell surface membrane:

phospholipid bilayer embedded with intrinsic and extrinsic proteins, with scattered glycolipids and glycoproteins

What are the functions of the nucleus?

act as the control centre of the cell, produce mRNA and tRNA, retain genetic material, manufacture ribosomal RNA and ribosomes

Describe the structure of the nucleus:

nucleolus and chromatin surrounded by a double membrane called a nuclear envelope, filled with nucleoplasm, covered in nuclear pores

What is a nucleolus in a nucleus?

small spherical region, manufactures ribosomal RNA and assembles ribosomes

What is chromatin in a nucleus?

mixture of DNA and proteins that form chromosomes

What is a nuclear envelope in a nucleus?

double membrane, continuous with the endoplasmic reticulum, controls entry and exit of materials

What are nuclear pores in a nucleus?

holes in the nuclear envelope which allow the passage of large molecules such as mRNA out of the nucleus

What is nucleoplasm in a nucleus?

granular, jelly-like material which makes up the bulk of the nucleus

What are the functions of a mitochondrion?

site of aerobic respiration, produce ATP from glucose

Describe the structure of a mitochondrion:

folded inner membrane forming cristae, surrounded by an outer membrane, filled with matrix

What are cristae in mitochondria?

folds in the inner membrane, provide a large surface area for the attachment of enzymes and proteins involved in respiration

What is the outer membrane in mitochondria?

half of the double membrane, controls the entry and exit of materials

What is the inner membrane in mitochondria?

half of the double membrane, folded to form cristae

What is the matrix in mitochondria?

mixture of proteins, lipids, ribosomes and DNA needed for protein synthesis, and enzymes needed for respiration

What are the functions of a chloroplast?

site of photosynthesis, absorb sunlight

Describe the structure of a chloroplast:

stacks of thylakoids called grana, surrounded by the chloroplast envelope, filled with stroma

What are thylakoids in a chloroplast?

disc-like structures, contain chlorophyll, site of the light dependent reaction

What are grana in a chloroplast?

stacks of thylakoids, joined by lamellae

What is the chloroplast envelope in a chloroplast?

double membrane, controls entry and exit of materials

What is the stroma in a chloroplast?

fluid, site of the light independent reaction, contains starch grains and enzymes

What are the functions of a Golgi apparatus?

form glycoproteins, produce secretory enzymes, secrete carbohydrates, transport, modify and store lipids and proteins, form lysosomes

Describe the structure of a Golgi apparatus:

a series of fluid-filled cisternae with vesicles at the edges

What are cisternae in a golgi apparatus?

flattened membranes, which molecules fuse to to be sorted

What is a lumen in a golgi apparatus?

inside the cisternae, where molecules are modified

What are vesicles in a golgi apparatus?

hollow structures which transport molecules to and from the golgi apparatus

What are the functions of a lysosome?

hydrolyse material ingested by phagocytes, release enzymes out of the cell, digest old organelles, autolysis

Describe the structure of a lysosome:

hydrolytic enzyme mixture contained in a lipid layer and membrane

What are hydrolytic enzymes in a lysosome?

enzymes which break down molecules, such as proteases, lipases, and lysozymes

What are lysozymes in a lysosome?

enzymes which break down the cell walls of certain bacteria

What is the function of a ribosome?

site of protein synthesis

Describe the structure of a ribosome:

a large sub-unit and a small sub-unit, both containing ribosomal RNA and proteins

What are the two types of ribosome?

70S, 80S

Where are 70S ribosomes found?

prokaryotic cells

Where are 80S ribosomes found?

eukaryotic cells

What are the functions of the rough endoplasmic reticulum?

synthesis of proteins and glycoproteins, provide a pathway for the transport of proteins

Describe the structure of the rough endoplasmic reticulum:

complex system of membranes enclosing cisternae, studded with ribosomes

Which type of endoplasmic reticulum has ribosomes?

rough

Which type of endoplasmic reticulum does not have ribosomes?

smooth

What are the functions of the smooth endoplasmic reticulum?

synthesise, store and transport lipids and carbohydrates

Describe the structure of the smooth endoplasmic reticulum:

complex system of membranes enclosing cisternae

What are the functions of a cell wall?

provides mechanical strength to the cell, provides mechanical strength to the plant, allows water to pass along it

What are the common features of all cell walls?

made of polysaccharides, have a thin layer called middle lamella between adjacent cell walls to stick them together

What substance makes up plant cell walls?

cellulose microfibrils

What substance makes up algal cell walls?

cellulose or glycoproteins or both

What substance makes up fungal cell walls?

chitin

What are the functions of a vacuole?

support plants by making cells turgid, store a solution of useful and waste substances

Describe the structure of a vacuole:

fluid-filled sac surrounded by a tonoplast

What is a tonoplast in a vacuole?

single membrane

What is the solution in a vacuole made up of?

sugars, amino acids, minerals, pigments and waste

Define ‘tissue’:

group of similar cells working together to perform a specific function

What is defined as ‘group of similar cells working together to perform a specific function’?

tissue

Define ‘organ’:

group of similar tissues working together to perform a specific function

What is defined as ‘group of similar tissues working together to perform a specific function’?

organ

Define ‘organ system’:

group of similar organs working together to perform a specific function

What is defined as ‘group of similar organs working together to perform a specific function’?

organ system

List the components of a eukaryotic cell:

cell membrane, nucleus, mitochondria, chloroplasts, golgi apparatus, lysosomes, ribosomes, endoplasmic reticulum, cell wall, vacuole, cytoplasm

List the components of a prokaryotic cell:

cell membrane, circular DNA, plasmids, slime capsule, cell wall, cytoplasm, flagella, ribosomes, pili, mesosomes

What is a slime capsule?

protective slimy outer layer, which retains moisture and helps the cell to adhere to surfaces and other cells

What are flagella?

tails which provide locomotion

What are plasmids?

loops of DNA which store genes to aid the survival of the cell

How do eukaryotic cells store DNA?

in a nucleus

How do prokaryotic cells store DNA?

in circular strands and plasmids

What substance makes up bacterial cell walls?

murein

What are pili?

hair-like structures which attach to other cells

What are mesosomes?

folds of the inner membrane, which contains enzymes required for respiration

Describe the structure of a bacterium:

plasmids, circular DNA and ribosomes floating in cytoplasm, surrounded by a membrane, cell wall and slime capsule, covered in pili and a flagellum

Describe the structure of a virus:

nucleic acids and enzymes surrounded by a capsid, floating in matrix surrounded by a lipid envelope, studded with attachment proteins

What are viruses?

acellular, non-living particles

What are bacteria?

unicellular, living organisms

What are the 2 types of microscope?

light, electron

How does a light microscope work?

a pair of convex glass lenses resolve images up to the wavelength of light apart

What are the types of electron microscope?

scanning, transmission

How does a scanning electron microscope work?

a beam of electrons is passed across the surface and scatters, creating a 3D image

How does a transmission electron microscope work?

a beam of electrons is passed through a thin section of the specimen, areas that absorb more electrons appear darker, producing a 2D photomicrograph

Name the limitations of TEMs and SEMs:

* the whole system must be in a vacuum so only dead specimens
* require a complex staining process
* require very thin specimens

Name the benefits of TEMs and SEMs:

• better resolution

• better magnification

Define ‘magnification’:

how many times bigger the image of an object is than the actual object

What is defined as ‘how many times bigger the image of an object is than the actual object’?

magnification

Define ‘resolution’:

the minimum distance apart two objects must be to be distinguishable

What is defined as ‘the minimum distance apart two objects must be to be distinguishable’?

resolution

What is the equation for magnification?

magnification = image size / object size

Describe the process of cell fractionation:

* cells are homogenised to form the homogenate
* homogenate is placed in a centrifuge and spun at a slow speed
* heaviest organelles collect at the bottom in a pellet
* supernatant is removed and spun again at a faster speed
* next heaviest organelles collect at the bottom in a pellet
* the process repeats until all organelles are separated

What solution must a sample be placed in before it can go through cell fractionation?

cold, isotonic, buffered

Why must the solution be cold for cell fractionation?

reduce enzyme activity that could break down organelles

Why must the solution be isotonic for cell fractionation?

prevents organelles from bursting or shrinking due to osmosis

Why must the solution be buffered for cell fractionation?

maintains constant pH so that proteins and enzymes do not denature

Can all cells in multicellular organisms divide?

no

What are the 3 stages of the cell cycle?

interphase, nuclear division, cytokinesis

What are the 4 stages of mitosis?

prophase, metaphase, anaphase, telophase

In which part of the cell cycle does DNA replication occur?

interphase

How many daughter cells are produced from mitosis?

2

How many daughter cells are produced from meiosis?

4

Describe the process of the cell cycle:

* interphase, cell grows, DNA and organelles are replicated, no division
* nuclear division, mitosis or meiosis, nucleus divides into either 2 or 4
* cytokinesis, replicated contents move to either side of the cell, cell splits in to two daughter cells

Describe the process of mitosis:

• prophase, chromosomes coil shorter, nucleolus disappears, centrioles move to opposite poles

• metaphase, chromosomes line up along equator, attached by centromeres

• anaphase, chromosomes separate into chromatids, spindle fibres contract

• telophase, chromatids reach opposite poles, split into two cells

What can uncontrolled cell division lead to?

tumours

Describe the process of binary fission:

* circular DNA replicates and attaches to cell membrane at opposite sides
* plasmids replicate
* cell membrane grows between DNA molecules, dividing cytoplasm in two
* new cell wall forms, creating two cells with identical circular DNA and some plasmids

What type of division happens in eukaryotes?

mitosis or meiosis

What type of division happens in bacteria?

binary fission

What type of division happens in viruses?

none, they are non-living