2.4 Cell Structure

Question 1

Relative sizes of molecules, organelles and cells

Answer 1

Minimum Minimum
resolvable Resolvable
By electron By light
microscope Microscope

0.1nm. 1nm. 10nm. 1000nm

Water Glucose. Ribosome. Red blood
Molecule. Cells

Question 2

What cells have a membrane and what is it made out of

Answer 2

In all cells

Outermost surface of cells

Composed out of mainly lipids and proteins

Provides sensory and structural support

Question 3

What is the nucleus

Answer 3

Only in eukaryotic cells (‘true but’ ‘true nucleus’)

Bound by a double membrane (nucleus envelope)

Organised into linear units called chromosomes

Made up of proteins and deoxyribonucleic acid (DNA)

Functional parts of chromosomes = genes

Question 4

Types of cells

Answer 4

Prokaryotic and eukaryotic

Question 5

What’s the Prokaryotic structure

Answer 5

Single-celled

Single, undivided internal structure of cytoplasm

Question 6

What is the structure of a eukaryotic cell?

Answer 6

Multicellular (animal, plants, fungi)
Complex internal structure:
Nucleus
Chromatin (coils of chromosomes)
Nucleolus (area in nucleus that produces ribosomes)
Mitochondria (contain ATP and help in cellular respiration)
Vesicles (flattened sacs used to transport material around cell)
Lysosomes (specialised forms of vesicles containing hydrolytic enzymes, break down pathogens and engulf worn out organelles)

Question 7

What are centrioles

Answer 7

Component of the cytoskeleton in eukaryotic cells.
Composed of microtubules.
2 associated centrioles form the centrosome which is involved in the assembly and organisation of the spindle fibres during cell division.

Question 8

What’s the function of the flagella and cilia

Answer 8

Flagella:
Used in cell motility and, in some cells, used as a sensory organelle detecting chemical changes in cells environment.

Cilia:
Can be mobile or stationary.
Mobile=beat in a rhythmic manner creating a current and cause fluids or objects to move.
Stationary=present on the surface of many cells and have important function in sensory organs

Question 9

What’s the structure of the nucleus and what does it do for DNA?

Answer 9

DNA directs the synthesis of all proteins required by the cell, even though protein synthesis happens at the ribosomes.

DNA controls metabolic activities of cell.

Biggest single organelle.

DNA is contained within a double membrane called a nuclear envelope. The envelope contains nuclear pores that allow molecules to move in and out of nucleus.

DNA is too large to leave nucleus so smaller sections, in form of RNA molecules, are transcribed to export nucleus for synthesis.

DNA associates with proteins called HISTONES to form a complex called CHROMATIN. Chromatin coils to form CHROMOSOMES.

Question 10

What’s the nucleolus

Answer 10

An area within the nucleus.

Responsible for producing ribosomes.

Composed of proteins and RNA.

RNA used to produced rRNA which combines with proteins to form the ribosomes needed for protein synthesis.

Question 11

What’s the structure and function of mitochondrion

Answer 11

Essential organelles in almost all eukaryotic cells.

Site of final stages of respiration in cells, where the energy stored in bonds of complex, organic molecules is made available for the cell to use by the production of ATP. Number of mitochondria in a cell is usually reflection of amount of energy it uses.

Have a double membrane; inner is highly folded to form CRISTAE and fluid interior is called a MATRIX.

Membrane forming cristae contains enzymes used in aerobic respiration.

Mitochondria also contains small amount of DNA called mtDNA (mitochondrial)

Question 12

What are vesicles

Answer 12

Membranous sacs that have storage and transport roles.

Consist of single membrane with fluid inside.

Used to transport material inside cell.

Question 13

What are lysosomes

Answer 13

Specialised forms of vesicles that contain hydrolytic enzymes.

Responsible for breaking down waste material in cells including old organelles.

Play a role in immune system because break done pathogens ingested by phagocytic cells.

Question 14

What organelles are involved in protein synthesis

Answer 14

Key function of cells is to synthesise proteins for internal use and secretion.
Significant proportion of internal structure of a cell is required for this process.

Ribosomes, endoplasmic reticulum, and Golgi apparatus are closely linked and coordinate the production of proteins.

Question 15

What is the endoplasmic reticulum

Answer 15

ER is a network of membranes enclosing flattened sacs called CISTERNAE.

Connected to outer membrane of nucleus.

2 types:
Smooth ER - synthesis and storage of lipids and carbohydrates.

Rough ER - (has ribosomes bound to surface) synthesis and transport of proteins.

Secretory cells which release hormones or enzymes have more RER than cells that don’t release proteins.

Question 16

What are ribosomes (to do with ER)

Answer 16

Can be free floating in cytoplasm or attached to ER, forming Rough ER.

not surrounded by membrane.

Constructed of RNA molecules made in nucleolus of cell.

Site of protein synthesis

Mitochondria and chloroplasts have ribosomes as do prokaryotic cells.

Question 17

What is the Golgi apparatus

Answer 17

Similar structure to Smooth ER.

Compact structure formed of CISTERNAE and does not have ribosomes.

Role in modifying proteins and packaging them into vesicles.

May be secretory vesicles if proteins are destined to leave cell; or lysosomes which stay in the cell.

Question 18

What is the process of protein production

Answer 18

1) proteins are synthesised on the ribosome bound to ER (RER).
2) pass into its cisternae.
3) packaged into transport vesicles.
4) vesicles move towards Golgi apparatus via transport function of cytoskeleton.
5) vesicles fuse with the CIS face of Golgi and proteins enter.
6) proteins are structurally modified before leaving Golgi.
7) proteins leave Golgi in vesicles from its TRANS face.
8) secretory vesicles carry proteins that are to be released from cell.
9) vesicles move towards and fuse with cell surface membrane.
10) release the contents through exocytosis.

Question 19

What is the structure of prokaryotic cells and where can they be found

Answer 19

able to live in extreme pH, temperature and salinity conditions.

Known as extremophiles - can be found on salt lakes and hydrothermal vents.

Usually in archaes domain. Always unicellular with simple structure.

DNA is not in a nucleus, have few organelles and aren’t membrane bound.

Question 20

How is DNA structured in prokaryotic cells

Answer 20

Packaged differently than in eukaryotes.

Have one molecule of DNA, a supercoiled chromosome to be compact.

Genes on chromosome are grouped into operons, meaning a number of genes are switched on or off at same time.

Question 21

What’s the size of ribosomes in prokaryotic cells

Answer 21

Smaller than in eukaryotes.

Relative size is determined by rate at which they settle or form sediment in solution.

Prokaryotic ribosomes are smaller so 70s (Larger eukaryotic ribosomes are 80s)

Both necessary for protein synthesis although the larger 80s ribosomes are involved in formation of more complex proteins.

Question 22

What is the cell wall in prokaryotic cells made of

Answer 22

Made from peptidoglycan also on one as murein.

Complex polymer formed from amino acids and sugars.

Question 23

How are flagella structured in prokaryotic cells

Answer 23

Thinner than equivalent structure in eukaryotes.

Don’t have 9+2 arrangement.

Energy to equate the filament that forms the flagellum is supplied from the process of chemiosmosis, not from ATP like in eukaryotes.

Attached to cell membrane of a bacterium.

Molecular motor causes the hook to rotate giving the filament a whip like movement which propels the cell.

Question 24

What’s different in a eukaryotic cell than a prokaryotic cell?

Answer 24

First eukaryotic cell appeared 1.5 billion years compared to prokaryotic appearing 3.5 billion years.

Eukaryotes are much more complex; their DNA is present in a nucleus and exist as multiple chromosomes to wrap around histones (proteins).
Prokaryotic cells have one chromosome that is supercoiled.

Eukaryotic genes can be turned on and off individually.

Plant, animal, fungi and protoctista are eukaryotic and multicellular.

Question 25

What are microfilaments (eukaryotic cell cytoskeleton)

Answer 25

Microfilaments (contractile fibres formed for actin; responsible for cell movement and cell contraction during cytokinesis)

Question 26

What are microtubules (eukaryotic cell cytoskeleton)

Answer 26

Microtubules (globular tubulin proteins polymerise to form tubes that determine shape of the cell - spindle fibres are made of microtubules)

Question 27

What do intermediate fibres do eukaryotic cell cytoskeleton

Answer 27

Intermediate fibres (give mechanical strength to cells and help maintain their integrity)

Question 28

What is the function of the cytoskeleton in a eukaryotic cell

Answer 28

Supports shape and stability of cell; controls movement of cell and movement within cell. 3 parts:
microfilaments
microtubules
intermediate fibres