E1: An introduction to cells

Question 1

Describe the cytosol

Answer 1

-water containing inorganic ions and small organic molecules and accounts for 70-80% of the weight of a living cell;
– Macromolecules (proteins, polysaccharides, lipids and DNA/RNA) account for the remaining weight of a cell.

Question 2

Describe the cytoplasm

Answer 2

semi-solid/fluid that typically defines all contents e.g., cytosol, organelles of the cell outside the nucleus and within the cytoplasmic membrane

Question 3

Describe the difference between bigger and smaller cells

Answer 3

-bigger cells have increasing complexity and function
-smaller cells have a simpler structure and greater ease of adaptability. Nutrients can diffuse more readily and larger surface area to volume ratio

Question 4

what is the generalised structure of a eukaryotic, human cell?

Answer 4

-highly organised, most have similar sub cellular components
-most cells have direct, specific interactions with neighbouring cells or extra cellular matrix

Question 5

Describe the nucleus

Answer 5

-double membrane structure with ER
-DNA packaged with proteins into super-coiled structure – chromatin to form
individual chromosomes in nuclear matrix
-contains the enzymes and proteins for regulation of DNA
-Several regions of RNA & protein called nucleoli
-nuclear pores which allow movement of small molecules, proteins and newly formed ribosomes
-typically single, ovoid structure

Question 6

what is the nuclear lamina?

Answer 6

a dense network of protein fibres that help provide structural integrity in the nucleus

Question 7

Describe the endoplasmic recticulum

Answer 7

-network of cisternae with interconnected lumen that links to nuclear membrane
-rough ER has attached ribosomes and smooth ER doesnt
-Proteins synthesized on the ER may undergo posttranslational modification inside the ER before being passed to the Golgi complex or lysosomes for further processing
-Serves as store of Ca2+, notably in muscle cells
-Involved in synthesis of lipids and steroids, and detoxification of drugs in liver cells

Question 8

what is the endoplasmic reticulum called in muscle cells?

Answer 8

sarcoplasmic reticulum

Question 9

Describe the golgi complex

Answer 9

-derived from ER but not connected
-stacks of flattened smooth membrane sacs and vesicles
* Processing and sorting of cytoplasmic membrane proteins and secretory proteins
* Many proteins undergo post-translational modification

Question 10

what does the cis (facing ER) part of golgi apparatus do?

Answer 10

receives proteins and lipids from ER

Question 11

what does the stack (main body) of the golgi apparatus do?

Answer 11

processes proteins and lipids

Question 12

what does the trans (facing cytoplasmic membrane) part of the golgi apparatus do?

Answer 12

targets delivery of proteins

Question 13

Describe the mitochondrion

Answer 13

-source of ATP
-double membrane structure
-Enzymes of electron transport chain (ETC) embedded in the inner membrane (cristae)
-Enzymes involved in Krebs cycle & fatty acid oxidation in matrix
-Has its own circular DNA, RNA and ribosomes

Question 14

Describe small organelles/ vesicles

Answer 14

-Lysosomes are derived from Golgi complex and contain various enzymes that work in an acidic environment, around pH 5.0 which is involved in breakdown of proteins, carbohydrates and lipids
-endosomes: sort and transport proteins and lipids within cells
-phagosomes: breakdown ‘foreign bodies’
-peroxisomes: involved in oxidation, reduction reaction

Question 15

Describe ribosomes

Answer 15

-site of translation
-Eukaryotes – 80S ribosome (60S and 40S)
-Prokaryotes – 70S ribosome (50S and 30S)
-complex of ribosomal RNA (rRNA) and ribosomal proteins

Question 16

what is the ‘S’ subunit in ribosomes

Answer 16

Svedberg unit and is sedimentation co-efficient; particles that differ in mass, shape and/or density sediment at different velocities

Question 17

Describe the cytoskeleton

Answer 17

-Consists of microfilaments, intermediate filaments and microtubules
-provides an internal scaffold, contributing to cell shape and movements
* Prokaryotes have a less elaborate cytoskeleton; cell wall provides structure

Question 18

Describe microfilaments (~7 nm in diameter)

Answer 18

-e.g., actin; provide/transmit mechanical support/signals
-actin binds many different proteins and contributes to a variety of cell
functions

Question 19

Describe intermediate filaments (~10 nm in diameter)

Answer 19

-e.g., keratin; desmin; mechanical strength, resistance to shear stresses

Question 20

Describe microtubles (~25 nm in diameter)

Answer 20

-e.g., tubulin; movement/separation of chromosomes – ‘mitotic spindle’
-Centrioles (organelles) found in animal cells (and some plants)
-Pairedstructures (centrosome)associated with mitosis
-single structures associated with cilia or flagella

Question 21

what protein fibres do muscle cells have and why?

Answer 21

actin and myosin (plus several accessory proteins) to facilitate cellular/ tissue contractile forces

Question 22

what are sarcomeres?

Answer 22

contractile fibres that are arranged into prominent structures in skeletal and cardiac tissues

Question 23

Describe the structure in smooth muscle cells

Answer 23

ack (or have less defined sarcomeres), with the actin filaments arranged obliquely within the cytoplasm and having defined anchor points in the cytoplasm (dense bodies) and cytoplasmic membrane (dense plaques) causing contraction in a twisting manner

Question 24

Describe the cytoplasmic membrane

Answer 24

formed by two phospholipid layers/leaflets, which, due to their amphipathic properties, assemble to form a closed bilayer structure

Question 24

Describe prokaryotes

Answer 24

-free DNA in cytoplasm, usually circular called nucleoid
-typically smaller genome (haploid), more rapid replication of their DNA
-smaller ribosomes
-lack membrane bound intra-cellular organelles or vesicles
-cell wall made of peptidoglycan

Question 25

role of peptidoglycan?

Answer 25

structure, shape and preventing osmolysis

Question 26

Describe viruses

Answer 26

-(20-300nm) that require a host to ‘live’ and evolves fast
-Supramolecular structures of nucleic acids, proteins and sometimes lipids and carbohydrates
-needs to infect a cell and use its machinery to reproduce
-simple but varied genomes

Question 27

Describe the anatomy of the virus

Answer 27

-capsid protects the genome
-viral proteins (capsomers) that protects genomic material
-encapsulates a small number of enzymes and proteins
-Some viruses have a membrane envelope that surround the capsid and facilitates host cell recognition

Question 28

what is tissue tropism

Answer 28

capsomers bind specific receptors on host cell surface and mechanism for viruses affecting specific cells or tissues and help facilitate invasion of the host cell

Question 29

Describe naked viruses

Answer 29

-Capsid only

Question 30

Describe enveloped viruses

Answer 30

-Capsid surrounded by lipid bilayer or ‘envelope’ derived from host cell membrane when it leaves the host the cell
-Envelope also contains viral proteins for targeting / infecting specific cell types

Question 31

Describe plasmids (bacteria)

Answer 31

-circular DNA and can replicate independently of main DNA
-carry few genes and are often associated with the ability to cause infections and antibiotic resistance

Question 32

smooth ER function?

Answer 32

involved with synthesis of fatty acids and detoxification reactions