Bio #1 Cell Structure and Function

What is the order of separation during ultracentrifugation (highest to lowest density)

Nucleus —> Mito/Chloro —> CSM —> Ribosome

Name all the parts consisting of the nucleus

1. nucleoplasm

2. nucleolus

3. nuclear envelope

4. nuclear pores

What is the structure of the nucleus

1. Ovoid or spherical

2. Double membraned (separated by a perinuclear space, inner is studded with ribosomes and is continuous with the membrane of the ER)

What is nucleoplasm

A semi-fluid matrix in the nucleus that contains enzymes, nucleotides, nucleoli and chromatin

What is the nucleolus

A dense region in the nucleoplasm that is not bounded by a membrane, it contains the DNA that codes for rRNA and is where ribosomal subunits are assembled

What are the 4 functions of the nucleus

1. Contain genetic info in the form of chromatin

2. Direct the synthesis of protein

3. Contain DNA that codes for rRNA

4. The location where ribosomal subunits are assembled (nucleolus)

What is the structure of mitochondria

1. Rod-shaped/Cylindrical

2. Double membraned (outer is smooth, inner is thrown into folds known as cristae)

3. Mitochondrial matrix

What does the mitochondrial matrix contain

1. 70s ribosomes

2. Circular DNA

3. Enzymes involved in the Krebs Cycle

What are the 2 functions of mitochondria

1. Synthesise ATP via respiration, to release energy needed for cellular activity

2. Release heat energy (in the process of respiration)

Describe the structure of a phospholipid

• Hydrophillic phosphate head that is negatively charged at one or more of its oxygen atoms

• Hydrophobic hydrocarbon chain

• Phospholipids are amphipathic

What are the components of the CSM

1. Phospholipids

2. Proteins

3. Glycoproteins

4. Glycolipids

5. Cholesterol

What are the 2 functions of the CSM

1. Regulate membrane fluidity

   • For CSM to fuse and fold during endocytosis and exocytosis

2. Restriction of movement of ions and polar molecules

How does the type of hydrocarbon (in phospholipids) affect membrane fluidity

Saturated hydrocarbon

• are able to pack closely together

• even at high temp, it does not become too fluid

Unsaturated hydrocarbon

• have kinks at the CC double bond

• cannot pack closely together

• even at low temp, it remains fluid

What happens when temp is very low and CSM solidifies

1. Permeability changes

2. Proteins embedded may not be able to function normally

How does presence of cholesterol affect membrane fluidity

At high temp

• cholesterol makes the membrane less fluid by preventing phospholipid movement

At low temp

• cholesterol disrupts the close packing of the membrane making it more fluid (prevent solidifying)

Decreases the permeability of membrane to ions and polar molecules

Why is the CSM selectively permeable

• Hydrophobic core only allows non-polar molecules to dissolve in the lipid bilayer and diffuse across it easily

• Ions and polar molecules are hydrophilic so they require specific transport proteins

• only small polar molecules like water can move through the hydrophobic core but very slowly

What are the 2 types of proteins embedded in the CSM

1. Extrinsic (loosely bound to either sides of the lipid bilayer)

2. Intrinsic

   • transmembrane proteins

   • either partly embedded or penetrate all the way through the lipid bilayer

In what type of cells is RER abundant in

Cells which secrete proteins (e.g. beta cells of islets of Langerhans that secrete insulin/WBC secreting antibodies)

In what type of cells is SER abundant in

Cells that are involved in lipid metabolism (synthesis and breakdown) (e.g. the gut, liver and glands)

What is the general structure of ER

It is a complex interconnected, membrane-bound cavities

What is the structure of RER (4 pts)

• interconnected, membrane-bound cavities in the form of flattened sacs called cisternae

• studded with ribosomes

• continuous with the nuclear envelope

• the inner surface of the membrane is embedded with enzymes involve in the chemical modification of synthesised polypeptides

What is the structure of SER (3 pts)

• interconnected, membrane-bound tubules that lack ribosomes

• continuous with the RER

• the inner surface of the membrane is embedded with enzymes involved in the synthesis of lipids and steroids

What are the 2 general functions of ER

1. they provide a large surface area for increased rate of reactions

2. they form an intracellular transport for materials to move from part of the cell to another through the lumen

What are the 2 functions of the RER

1. Cisternae provides an environment for

   • polypeptide to fold into its specific 3D conformation

   • post-translational chemical modification (glycosylated)

2. proteins synthesised at the RER are transported to the GA for secretion out of the cell

   • proteins destined to be membrane proteins are inserted into the RER membrane —> eventually becomes part of a vesicle membrane —> fuse with CSM

What are the 4 functions of the SER

1. synthesise lipids

   • phospholipid synthesis to replenish or form membranes (especially during cell division)

2. detoxification of drugs and poison in liver cells

3. stores and releases calcium ions in the muscle cells for muscle contraction

4. metabolises carbohydrates such as glycogen to glucose

What is the structure of Golgi Apparatus (3 pts)

• stack of membrane-bounded flattened sacs known as cisternae

• has a cis face (receiving) and a trans face (secreting)

• each cisterna has a specific set of enzymes

How does material packaged in a vesicle enter, move through and exit the GA

Enter

• vesicle fuses with the GA membrane at the cis face and release its contents into the GA cisternae

Move through

• the material is processed and move through cisternae to cisternae towards trans

Exit

• the secretory vesicle containing the secretory molecules at the trans face pinches off from the cisternae and move along microtubules towards the surface of the cell —> release contents to exterior

• vesicles containing hydrolytic enzymes will remain in the cell as lysosomes

What are the 2 functions of the GA

1. MSP (modify, sort and package) substances from the ER into vesicles for secretion or for use within the cell

2. synthesis carbohydrates

What is the structure of lysosomes (2 pts)

• membrane-bound sacs that contain hydrolytic enzymes that hydrolyse complex substances into simpler ones

• acidic pH (unlike cytoplasm which is neutral) this is the optimum pH for the enzymes

What are the 3 functions of lysosomes

1. Disposal of defunct or surplus organelles

   • fuses with the unwanted cellular organelle

   • discharge its contents

   • the organelle is broken down by the enzymes and the soluble products are absorbed into the cytoplasm where they are used to form new organelles

2. Digestion of ingested particles

   • lysosome fuse with endocytic vesicle containing ingested particles

   • intracellular digestion takes place by the enzymes

   • digested products are absorbed into the cytoplasm and assimilated

   • undigested products are excreted out of the cell

3. Cell autolysis

   • the lysosome membrane ruptures, releasing the enzymes into the cell cytoplasm

   • breaks down all the organelles and kills the cell

   • necrosis (unintended), apoptosis (programmed)

   • occurs in dying or damaged cells

What is the structure of chloroplast

• double membraned

• biconvex, disk-shaped

• in the stroma, there are 40-80 grana

• each grana is a stack of thylakoids connected by tubules called intergrana to adjacent grana

Which cell organelle is the largest

Nucleus

Which cell organelle is the second largest

Chloroplast

What is embedded on the thylakoid membranes (3 pts)

1. photosynthetic pigments

2. electron carriers

3. ATP synthase

What does the stroma consist of

1. 70s ribosomes

2. circular DNA

3. enzymes involved in the Calvin cycle

4. starch granules

What does the circular DNA in chloroplast code for

Code for chloroplast proteins involved in photosynthesis (e.g. rubisco, ATP synthase) and rRNA

Having membrane-bound organelles allows to cell to be ___

compartmentalised

What are the 5 advantages of having membrane-bound organelles

1. physically separate chemical reactions, many of which are incompatible

   • allows the localisation of specific enzymes/molecules to specific compartments

   • allows specialisation of cells —> diff comp perform diff f(x)

2. temporally separate diff chemical reactions

   • molecules are produced or processed in one organelle, then are used in other reactions (increase efficiency)

   • e.g. transcription & translation

3. provides a surface for attachment of proteins for specific functions

   • larger SA, more proteins

   • proteins can be arranges in specific order and orientation

4. allows higher conc enzymes and molecules to accumulate in the comportment

   • more effective collision between enzyme and substrate (increase efficiency)

5. provides optimal conditions for specific reactions

   • biomolecules require a specific condition for it to maintain its specific 3D conformation

What is the structure of ribosomes

• each ribosome has two subunits (large and small)

• each subunit consists of ribosomal RNA and ribosomal proteins

• ribosomal subunits are assembled in the nucleolus

Where are the 70s ribosomes in eukaryotic cells

Mitochondria and chloroplast

Where are free ribosomes and what are their functions

Location: in the cytoplasm

Function: synthesis protein to be used within the cytoplasm or transported to other organelles

Where are bound ribosomes and what are their functions

Location: bounded to the outer surface of the RER and nucleus, either singly or in chains (polyribosomes—> increase rate of translation)

Function: synthesis protein to be secreted out of the cell OR inserted into membranes OR packaged within certain organelles (lysosome)

Centrioles are found in the centrosome of ____cells

Animal cells

(Plants have centrosome but no centriole)

How many pairs of centrioles per cell? (Both normal and dividing)

Normal - 1 pair

Dividing - 2 pair

What is the structure of centrioles

• found as a pair, which lie at right angles of each other

• each centriole consist of a hollow tube

• the walls of the hollow tube are made up of nine triplets of microtubules

What are microtubules

Microtubules are tubular structures which are made up on proteins called tubulin

What are the functions of centrioles

1. The centrosome is the microtubule organising centre (MTOC) which organises the formation of meiotic and mitotic spindle fibres

2. The centrioles give rise to the basal bodies of cilia or flagella in sperm cells

What are the structures always present in all prokaryotes (5 pts)

• peptidoglycan cell wall

• cell surface membrane

• 70s ribosomes

• bacterial chromosome

• cytoplasm

What membrane bound organelles do prokaryotes have

PSYCH THERE ARE NO MEMBRANE BOUND ORGANELLES

Why is the cell wall of prokaryotes strong and rigid

due to the presence of peptidoglycan, a molecule that consists of parallel polysaccharides chains cross-linked at regular intervals by short amino acid chains, cross linking provides high tensile strength

What are the functions of the peptidoglycan cell wall (3 pts)

• help the cell maintain its shape and structure

• forms a meshwork permeable to water, ions and small molecules. enzymes and DNA can pass through

• it helps as to anchor appendages like flagella and pili (which originate from the cytoplasm and protrude through the cell wall to the exterior)

What are the things found in bacteria cytoplasm

• 70s ribosomes

• bacterial chromosome

• plasmids

What are plasmids

small extra-chromosomal molecules of circular DNA that contains genes that provide some benefit to the bacteria but are not essential for survival

Why does transcription and translation occur concurrently in bacteria

Lack of nuclear envelope —> the mRNA is translated before transcription is complete

What is the structure of bacterial chromosome

single, circular and double stranded DNA associated with DNA-binding non-histone proteins

How are plasmids passed down/inherited

• replicated before cell division (replication is independent from main chromosome)

• there are several and they are divided into the daughter bacteria in a random manner

• unequal inheritance of plasmid number

How do bacteria divide

binary fission

Can viruses be seen under a light microscope

NO

Why are viruses regarded as obligate parasites

they depend on eukaryotes and prokaryotes to reproduce

The capsid is highly symmetrical. What are the two types of symmetry

1. helical (rod-shaped viruses)

2. polyhedral (spherical-shaped viruses)

   • icosahedral (20 sided)

What is the structure of viral genome

• single or double stranded

• DNA or RNA but never both

• circular or linear

What is the function of viral genome

code for synthesis of viral proteins like capsid and enzymes

What is nucleocapsid

It is the combined structure of both the viral genome and the capsid

What is the function of capsid

Protect the virus from environmental damage and facilitates the introduction of the viral genome into host cells

What are the 3 additional structures of viruses (in syllabus)

• tail

• envelope

• viral enzymes

What is the viral envelope composed of? and where is each component derived from

phospholipids

• derived from the host cell surface membranes by budding

glycoproteins

• coded by the viral genome

What is the function of viral envelope

• serves as an additional protective coat

• glycoprotein spikes serve to attach the virus to specific receptors on the host cell

What is viral specificity

Viruses have specific glycoproteins that can only attach to specific types of host cell

What is the name of the virus that only infects bacteria

bacteriophage

What does the tail of the bacteriophage consist of

Base plate, tail fibres and contractile sheath attached to the capsid head

What is the function of the tail of some viruses

to attach the bacteriophage to the bacterium. base plate and tail fibres are involved in the binding of the phage to the bacterium while contractile sheath contracts to inject the phage DNA into the host bacterium

What and where are viral enzymes located

viral enzymes are enzymes that are not found in host cells, they are located in the capsid

Prokaryotes are only unicellular, eukaryotes are only multicellular (True or False)

False. Eukaryotes can be unicellular

What is the glycocalyx

The carbohydrate-rich layer outside the plasma membrane

What are the 3 functions of glycocalyx

1. Cell-cell adhesion

   • bind cells together to form tissues

2. Cell-cell recognition

   • enables one cell to distinguish one cell type from another

3. Act as receptor sites

   • for chemical signals, ligands to bind

What are the 6 functions of proteins and glycoproteins in the membrane

1. Transport

   • channel protein and carrier proteins

2. Enzymatic activity

   • e.g. ATP synthase

3. Signal transduction

   • receptor that receives ligands to initiate a reaction to relay a signal to the cell

4. Cell-cell adhesion

5. Cell-cell recognition

6. Attachment to cytoskeleton and extracellular matrix

   • bind to cytoskeleton and to extracellular proteins in the matrix

   • helps the cell maintain its shape and stabilise the position of certain membrane proteins

What are water channel proteins called

aquaporins

What are the 3 types of endocytosis

• Pinocytosis

  • uptake of fluid or solutes dissolved in that fluid

  • non specific

• Phagocytosis

  • uptake of large molecules

  • phagocytic cell extends pseudopodia and engulfs particle

• Receptor mediated endocytosis

  • ligand binds to the receptor, causing CSM to invaginate

When there is endocytosis, why is exocytosis needed

CS membrane and membrane proteins are removed in the process of endocytosis, exocytosis replenishes what was lost —> secretory vesicles fuses with CSM, adding the membrane and membrane proteins to the CSM