Basic Cell Biology

Question 1

Describe the Nuclear envelope

Answer 1

• double membrane
• separates nucleus from cytoplasm
• continuous with lumen of endoplasmic reticulum
• nuclear pores (100nm)
• aid & regualte exchange of proteins

Question 2

Describe histones

Answer 2

Proteins that aid in folding of DNA in chromosomes to tightly pack it

Question 3

Describe Chromatin

Answer 3

• complex of histones & DNA that make up the chromosomes inside the nucleus
• 2 classes = Heterochromatin & Euchromatin

Question 4

Describe Heterochromatin

Answer 4

• tightly condensed throughout cell cycle
• generally inactive in transcription

Question 5

Describe Euchromatin

Answer 5

• less condensed
• contains actively transcribed genes

Question 6

Describe the Nucleolus

Answer 6

• membraneless part of nucleus
• involved in production & assembly of ribosomes
• assembles ribosomes from >50 different proteins & 3 RNA molecules

Question 7

Describe the Cytoskeleton

Answer 7

• cellular scaffolding contained within cytoplasm in all cells
• dynamic structure
• maintains cell shape, protects cells, enables cellular motion

Question 8

What 3 filaments are found in a eukaryotic cytoskeleton ?

Answer 8

• microfilaments (actin)
• intermediate filaments
• microtubules

Question 9

Describe Microfilaments (Actin)

Answer 9

• most conc. beneath cell membrane
• composed of 2 intertwined actin chains

Question 10

What are the functions of microfilaments ?

Answer 10

• resisting tension, maintianing cellular shape
• essential for signal transduction
• important for cytokinesis, muscular contraction & cytoplasmic streaming

Question 11

Describe Intermediate Filaments

Answer 11

• more stable than actin filaments
• heterogeneous constituents of the cytoskeleton
• throughout the cell

Question 12

What are the function of intermediate filaments ?

Answer 12

• like actin they function in the maintenance of cell-shape by bearing tension
• organise internal 3D cell structure
• anchors organelles
• structural components of nuclear lamina

Question 13

Describe the composition of intermediate filaments

Answer 13

• vimentins - common structural support of many cells
• keratin - found in skin, cell, hair & nails
• neurofilaments of neural cells
• lamin - giving structural support to nuclear envelope

Question 14

Describe Microtubules

Answer 14

• made of alpha & beta tubulin, have very dynamic behaviour
• constantly elongated & shortened
• form a ring around nucleus & radiate out from this ring
• resists compression compared to other cytoskeletal filaments

Question 15

What are the functions of microtubules?

Answer 15

• made of protofilaments
• polymers of alpha & beta tubulin dimers
• bundle in hollow cylindrical filaments 25nm diameter
• lumen is approx. 15nm in diameter
• arranged in imperfect helix

Question 16

Describe centrioles

Answer 16

• nine triplet sets
• involved in organisation of mitotic spindle & in completion of cytokinesis
• position determines position of nucleus

Question 17

Describe mitochondria

Answer 17

• membrane enclosed organelle
• composed of compartments that carry out specialised functions
• involved in cell signalling, cell differentiation & cell death
• inner & outer membrane

Question 18

Describe the mitochondrial outer membrane

Answer 18

• encloses entire organelle
• contains large number of integral proteins called porins
• channels that allow molecules <5000 Da to freely diffuse across

Question 19

Describe the mitochondrial intermembrane space

Answer 19

• same conc. of small molecules as cytosol
• freely permeable
• proteins composition differs to cytosol
• 1 protein localised to intermembrane space is cytochroeme C = part of electron transport chain

Question 20

Describe the mitochondrial inner membrane

Answer 20

• contains proteins with 4 functions
  1. those that perform redox reactions of oxidative phosphorylation
  2. ATP synthase, generates ATP in matrix
  3. specific transport proteins that regulate metabolite passage in & out matrix
  4. No porins & highly impermeable

Question 21

Describe ATP Synthase

Answer 21

• enzyme that synthesises ATP from ADP & inorganic phosphate
• ATP synthesis uses energy
• protons (H+) moving down an electrochemical gradient from inter-membrane space into matrix

Question 22

What are Cristae?

Answer 22

• invaginations of inner membrane of mitochondria
• expand the SA of inner mitochondrial membrane
• enhances its ability to produce ATP

Question 23

Describe the lipid presence in the inner mitochondrial membrane

Answer 23

• very high protein : phospholipid ratio - usually 3:1
• rich in a phospholipid called = cardiolipin
• cardiolipin contains 4 fatty acids & helps make inner membrane impermeable

Question 24

Describe the mitochondrial membrane

Answer 24

• space enclosed by inner membrane
• contains;
• 2/3 of total protein in mitochondrion
• highly concentrated mix of hundred of enzymes
• tRNA
• special mitochondrial ribosomes

Question 25

How did mitochondria arise ?

Answer 25

- endosymbiotic theory - mitochondria are descended from ancient bacteria, which were engulfed by ancestors of eukaryotic cells more than a billion years ago - we know this as mitochondria contian organelles

Question 26

Describe the endoplasmic reticulum

Answer 26

- interconnected network of tubules, vesicles and cisternae - cisternae = sac-like structures held together by cytoskeleton - membrane encloses the cisternal space from cytosol

Question 27

Describe the functions of the endoplasmic reticulum

Answer 27

- protein translation, folding & tranport of proteins for the cell membrane & transmembrane receptors

Question 28

What are the 3 varieties of ER?

Answer 28

1. Rough endoplasmic reticulum 2. Smooth endoplasmic reticulum 3. Sarcoplasmic reticulum

Question 29

Describe the RER

Answer 29

- Surface is studded with ribosomes - membrane continous with outer layer of nuclear envelope - key in producing - lysosomal enzymes & secreted proteins

Question 30

Describe the SER

Answer 30

Functions in other metabolic processes: - synthesis of lipids & steroids - metabolism of carbs - drug detoxification - steroid metabolism

Question 31

Describe the Sarcoplasmic Reticulum

Answer 31

- special type of ER found in smooth & striated muscle - contains large stores of calcium - sequesters & releases when the cell is depolarised - triggers muscle contraction

Question 32

Simply describe the cell cycle

Answer 32

- series of temporally ordered events that leads a cell to divide itself into 2 daughter cells

Question 33

What are the characteristics of the cell cycle?

Answer 33

- temporally ordered events - cannot go backwards - positive & negative feedback loops regualte function of molecules involved - checkpoints maintain order of events in case something goes wrong

Question 34

When do cell numbers change?

Answer 34

- growth & development - tissue turnover - response to injury - physiological changes

Question 35

Describe the cell cycle

Answer 35

- divided into 2 morphological & 4 biochemical stages 1. interphase = first gap, replication of chromosomes & second gap (G1, S, G2) 2. mitosis & cytokinesis = mitosis (M)

Question 36

Describe the Mitotic (M) Phase

Answer 36

- division of nucleus resulting in identical complete copies of chromosomes packaged into 2 new nuclei - mitosis is divided into 4 phases = prophase, metaphase, anaphase & telophase

Question 37

Describe prophase

Answer 37

chromatin condenses into chromosomes

Question 38

Describe metaphase

Answer 38

Spindle forms from microtubules & chromosomes align at the equatorial plane

Question 39

Describe anaphase

Answer 39

sister chromatids separate

Question 40

Descrobe telophase

Answer 40

- cell division

Question 41

Give an overview of mitosis

Answer 41

- produces 2 daughter cells - these daughter cells contain the exact same number of chromosomes as orginial parent cell - daughter cells are diploid