Biology: Cell Ultrastructure

What does the Cell Theory state? (3)

The Cell Theory states that:

1. The cell is the smallest, most basic unit of life that carries out all essential life processes.

2. All living organisms are made up of cells.

3. All cells arise from pre-existing cells via cell division.

What are the two main types of cells?

Eukaryotic cells and Prokaryotic cells

Is a chloroplast visible when stained under a light microscope?

Yes, due to chlorophyll

Is the nuclei visible when stained under a light microscope?

Yes

Are starch grains visible when stained under a light microscope?

Yes

Is a vacuole visible when stained under a light microscope?

Yes

Do electron micrographs or light micrographs show more detail?

Electron micrographs show more detail.

Is a nucleus a non-membrane, single-membrane or a double-membrane organelle?

Double membrane

Is a mitochondrion a non-membrane, single-membrane or a double-membrane organelle?

Double membrane

Is a chloroplast a non-membrane, single-membrane or a double-membrane organelle?

Double membrane

Is the smooth ER a non-membrane, single-membrane or a double-membrane organelle?

Single membrane

Is the rough ER a non-membrane, single-membrane or a double-membrane organelle?

Single membrane

Is the lysosome a non-membrane, single-membrane or a double-membrane organelle?

Single membrane

Is the secretory vesicle a non-membrane, single-membrane or a double-membrane organelle?

Single membrane

Is the vacuole a non-membrane, single-membrane or a double-membrane organelle?

Single membrane

Is the nucleolus a non-membrane, single-membrane or a double-membrane organelle?

Non-Membrane Bound

Is the ribosome a non-membrane, single-membrane or a double-membrane organelle?

Non-membrane Bound

Is the centriole a non-membrane, single-membrane or a double-membrane organelle?

Non-membrane Bound

What is the shape of the nucleus?

Spherical or ovoid

What is the largest organelle within the eukaryotic cell?

Nucleus

What is the nucleus bounded by?

Nuclear envelope

What is the nuclear envelope made out of?

An outer membrane and an inner membrane

What does the nuclear envelope contain, and in turn, what does that contain?

The nuclear envelope contains the nucleoplasm, which contains chromatin, enzymes and the nucleolus.

What is the function of the nucleus?

1. Contain and store hereditary / genetic material (DNA)

2. Control cellular activities by regulating the rate of protein synthesis, specifically transcription

What is the difference between the cytoplasm and the cytosol?

The cytoplasm is where membranes are bound while cytosol is a fluid.

Is the nuclear envelope a non-membrane, single-membrane or a double-membrane?

Double membrane

How many phospholipid layers and bilayers does a double-membrane have?

Two phospholipid bilayers → meaning four phospholipid layers

What is continuous with the rough and smooth endoplasmic reticulum?

The outer membrane of the nuclear envelope

Why is protein synthesis allowed in the outer membrane of the nuclear envelope?

Ribosomes are bound

What is directly connected with the lumen of the ER that allows for protein transport?

The space between inner and outer nuclear membranes of the nuclear envelope

What is the inner membrane of the nuclear envelope lined with?

Nuclear lamina

What is the nuclear lamina and what is its main function?

It is a network of protein filaments that provide support for the nucleus.

What is the nuclear matrix?

A network of protein fibres

The nuclear envelope, together with the nuclear matrix, help to organise ____.

DNA

The nuclear envelope is perforated by ___.

nuclear pores

Nuclear pores are surrounded by ___

Nuclear pore complexes

What is the function of the nuclear pore complexes?

Allow certain substances and macromolecules to move through / Control movement of water-soluble substances

The nuclear pore complexes allows entry of:

• Free ribonucleotides (adenine, uracil)

• RNA polymerase for transcription

• Transcription factors

• Ribosomal proteins

The nuclear pore complexes allows exit of:

• Mature mRNA and tRNA to cytoplasm for translations

• Ribosomal subunits

What is the nucleoplasm?

A semi-fluid matrix that fills the nucleus

What does the nucleoplasm contain?

• Nucleolus

• DNA in the form of chromatin / Chromosomes

• Enzymes

What does the nucleolus contain?

The rRNA genes that code for ribosomal RNA which combines with ribosomal proteins to form ribosomes

What is the function of the nucleolus?

• Site of synthesis of ribosomal RNA

• Partial assembly of ribosomes

• Contains rRNA genes

If there is no nucleolus, ___ cannot be synthesized and hence, ____ cannot occur.

ribosomes

protein synthesis

The majority of the cell’s genetic material is located in the ____.

nucleus

DNA is associated / completed with ____ proteins to form ____. This allows the long DNA molecules to ____.

histone

chromatin

fit into the nucleus

DNA is wound around histone proteins to form ____ fibres in _____, and further ____ to form ____ in dividing cells.

histone

non-dividing cells

condensation

chromosomes

In a non-dividing cell, the DNA chromosomes are not visible because they are extended into ______, appearing as: _____ and _____.

threadlike strands

Heterochromatin and Euchromatin

Compare heterochromatin and euchromatin.

• Heterochromatin

  • Highly compact

  • Condensed DNA appear darker

  • Genes are seldom / not transcribed.

• Euchromatin

  • Less compact

  • Condensed DNA (active transcription) appear lighter

  • Genes are frequently transcribed.

Prior to cell division, the chromatin fibres ____ and become visible as _____ during _____.

Condense

Chromosomes

Prophase

In the nucleus, you can find enzymes required for processes like:

• DNA replication

• Transcription

• Post-transcriptional modification

• Extension of telomere

What is the difference between a nucleus and a nucleolus?

• A nucleus has a double-membrane and a nucleolus has no-membrane.

• The nucleus stores hereditary materials and controls cellular activities while a nucleolus is the site of synthesis for rRNA, and partial assembly of ribosomes.

Each ribosome consists of ___ subunits. Name them.

two

The large subunit and the small subunit

Eukaryotes have ___S ribosomes.

60S + 40S → 80S

Prokaryotes have ___S ribosomes.

50S + 30S → 70S

Each ribosome subunit is composed of ____ and ____.

rRNA and ribosomal proteins

What is the function of a ribosome?

To synthesise proteins (translation of mRNA)

Free ribosomes in the cytosol synthesise cytosolic proteins that function within the ____.

cytosol

Ribosomes attached to the rER synthesize proteins for ______ as enzymes in _____, or as enzymes incorporated into the _____.

secretion out of the cell

lysosomes

cell surface membrane

Multiple ribosomes may be attached to the same mRNA for simultaneous translation, thus forming ____ / polysomes.

polyribosomes

Both ER are an extensive network of ____________ called cisternae or cisterna.

interconnecting membranous tubules and flattened sacs

What are the cisternae in ER?

Extensive network of interconnecting membranous tubules and flattened sacs

Both ER originate from the ______ of the ______.

outer membrane

nuclear envelope

Why does the rER appear rough?

Presence of ribosomes

The cisternae of the rER are interconnected with each other and are continuous with the outermembrane of the ___.

nuclear envelope

What are the functions of the rER?

• Attached ribosomes provide the site of protein synthesis

• Packaging of proteins in ER vesicles for transport to other parts of the cell (e.g. GA)

The surface of rER has ____ for attachment of ribosomes for ___ of mRNA.

receptor sites

translation

In rER, the polypeptide synthesised by ribosome passes through the channel of the receptor protein into the _____ of the rER as ____ proceeds.

lumen

protein synthesis

Tell me how a protein / polypeptide is synthesised and packaged into an ER Vesicle.* (6)

1. A short polypeptide chain is synthesised by a free ribosome.

2. ER signal peptide attaches to the receptor site so that ribosome is attached to rER.

3. The polypeptide synthesised by the ribosome passes through the channel of the receptor into the rER lumen.

4. When the protein is released from the ribosome, it folds into its tertiary structure.

5. The protein is enclosed in a transport / ER vesicle, which buds off from the rER.

6. The transport vesicle travels along microtubules of cytoskeleton to cis face of GA where further protein modifications take place.

Why is the sER smooth?

Absence of ribosomes on its surface

The sER is more ____ than the rER and there are many single membrane flattened sacs known as _____ with numerous ______ budding off.

Tubular

Cisternae

Vesicles

What are the functions of the sER? (4)

1. Site of synthesis of lipids, phospholipids, cholesterol and steroid hormones

2. Site of detoxification of poisons and drugs (in liver cells)

3. Storage of calcium ions (in muscle cells)

4. Glycogen synthesis  

The GA consists of stacks of flattened, curved membranous sacs known as ____ that are not interconnected.

cisternae

What are the functions of the GA? (3)

1. Site where substances made in the rER and sER are chemically modified, sorted, packaged, and transported for secretion out of the cell or delivery to other parts of the cell / organelles

2. Form lysosomes

3. In plant cells, site of synthesis of certain polysaccharides (e.g. pectin and other non-cellulose polysaccharides) used for the synthesis of the cell wall

The ER vesicles containing proteins (rER) / lipids (sER) travel along microtubules of the cytoskeleton and fuse with the _____ of GA.

cis face

Proteins / Lipids move from cis face to _____ of the GA by repeated ______________________ from from one cisterna and then fusing with ______. _________ occurs.

trans face

budding of Golgi vesicles

another cisterna

Biochemical modification

The _____ is the site where post-translational modifications occur.

GA

_____ is the addition of short carbohydrates chain to proteins to form glycoproteins like antibodies, or to lipids to form glycolipids like cell surface antigens on RBC

Glycosylation

Glycosylation is the addition of _______ to proteins to form glycoproteins like antibodies, or to lipids to form glycolipids like cell surface antigens on RBC

short carbohydrate chains

_____ is the addition of phosphate group to proteins (to either activate or deactivate protein, depending on the type of protein

Phosphorylation

Phosphorylation is the addition of ______ to proteins (to either activate or deactivate protein, depending on the type of protein

phosphate group

At the _____, modified proteins / lipids are sorted and packaged into fresh vesicles.

trans face

How does GA help form cell wall in plant cells?

1. GA vesicles containing new cell walls materials (except cellulose) move to the middle of the cell.

2. The GA vesicles fuse to form the cell plate, subsequently forming the new cell membrane, while the contents of the GA vesicle form the cell wall of the daughter cells.

Lysosomes are small _____ vesicles of 0.1-0.5 micrometres.

spherical

Lysosomes are formed from the ____.

GA

Lysosomes contain _____ like proteases, glycosidases, lipases and nucleases that break down proteins, carbohydrates, lipids and nucleic acids.

hydrolytic enzymes

The hydrolytic enzymes in lysosomes require ____.

low pH / acidic

How do lysosomes maintain the acidic conditions needed for the hydrolytic enzymes?

By a proton pump on the lysosome membrane, which pumps protons from the cytosol into the lysosome

What are the functions of a lysosome? (4)

1. Digest / break down substances taken in by endocytosis

2. Autophagy

3. Autolysis

4. Release enzymes outside the cell

What is autophagy?

Damaged or worn-out organelles within the cell are engulfed and digested within lysosomes

Autolysis

Contents of lysosome are released within the cell (usu. injured cells or dying tissue) to break it down

Lysosomal enymes may be released out of the cell during…

fertilisation, remodelling of bone and replacement of cartilage during development

What shape is the mitochondrion?

Rod or cylindrical-shaped

The outer and inner membranes of the mitochondrion are separated by the _______.

intermembrane space

The mitochondrion is bound by the _______.

mitochondrion envelope

The mitochondrion envelope is made up of:

Outer membrane and Inner membrane/Cristae

The mitochondrion contains a matrix that contains:

Circular DNA

70S ribosomes

Enzymes

Is the outer membrane of the mitochondrion a smooth continuous boundary or rough?

Smooth continuous boundary

The outer membrane of the mitochondrion contains transport proteins that allow ______ molecules to enter the intermembrane space. It is impermeable to ____.

water-soluble

ions

The inner membrane of the mitochondrion is extensively folded to form ____ which project into the aqueous interior called the __________.

cristae

mitochondrial matrix