BSC2010 Chapter 6

The Cell

What is the simplest living unit which all organisms are made up of?

Cells

Who discovered the cell?

Robert Hooke

What microscope did Hooke use to study the cell?

The light microscope (LM)

How does the light microscope magnify an image?

The lenses refract (bend) the light so the image appears magnified.

What are the three important parameters of microscopy?

Magnification, Resolution, Contrast

What is Magnification in microscopy?

The ratio of an objects image size in respect to its real size.

What is Resolution in microscopy?

The measure of the clarity of an image or the minimum distance of two distinguishable points.

What is Contrast in microscopy?

Visible differences in brightness between parts of the sample.

What are organelles?

Specialized structures inside cells that perform specific functions—organs for cells.

What is a major faulty of the light microscope in respect to the study of cells.

The resolution is too low to study organelles.

What are the two basic types of electron microscopes (EMs)?

Scanning EM and Transmission EM

How does the Scanning EM operate?

It focuses a beam of electrons onto the surface of a specimen, providing images that look 3D.

How does the transmission EM operate?

It focuses a beam of electrons through a specimen.

What are Transmission EMs mainly used to study?

The internal structure of cells.

Cell Fractionation

A laboratory technique used to break open and separate their internal components so they can be studied individually.

What are the two domains of life?

Prokaryotic and Eukaryotic

Basic features of all cells:

1. Plasma membrane

2. Cytosol

3. Chromosomes

4. Ribosomes

Cytosol

The fluid portion of the cytoplasm inside a cell. It is a jelly-like, watery substance where organelles like the nucleus, mitochondria, and ribosomes are suspended.

Ribosomes

Tiny organelles found in all living cells, and their main job is to make proteins — which are essential for virtually every cell function.

Prokaryotic cells are characterized by having:

1. No nucleus

2. DNA in an unbound region called the nucleoid

3. No membrane-bound organelles

4. Cytoplasm bound by the plasma membrane

Nucleoid

The region inside a prokaryotic cell (like bacteria) where the cell’s genetic material (DNA) is located.

Cytoplasm

The entire contents of a cell between the cell membrane and the nucleus (in eukaryotic cells) and the plasma membrane (in prokaryotic cells).

Eukaryotic cells are characterized by having:

1. DNA in a nucleus that is bounded by a membranous nuclear envelope

2. Membrane-bound organelles

3. Cytoplasm in the region between the plasma membrane and nucleus

Which cells are larger, eukaryotic or prokaryotic?

Eukaryotic

Plasma membrane

A selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell.

Why is the surface area to volume ratio of a cell important?

As a cell increases in size, it volume grows proportionately more than its surface area. So, the surface area can’t keep up with the cell’s increasing needs to get nutrients in and waste out.

What type of cells have internal membranes that partition the cell into organelles?

The eukaryotic cell

What are membranes made out of?

Double layer of phospholipids and other lipids

Where is most of the DNA in a eukaryotic cell located?

The nucleus

What do ribosomes use DNA to do?

To make proteins

Nucleus

Contains most of the cell’s genes and is usually the most conspicuous organelle because of its large size and central position in the cell.

Nuclear Envelope

Encloses the nucleus and separates it from the cytoplasm.

What is the structure of the nuclear membrane?

A double membrane, each consisting of a lipid bilayer.

The nuclear membrane is lined with pores, what do they do?

Regulate the entry and exit of molecules from the nucleus.

Nuclear Lamina

Lines the inside of the nuclear envelope and is composed of proteins and maintains the shape of the nucleus.

Chromosomes

Long, thread-like structures made of DNA and proteins which carry genetic information.

Chromatin

DNA and proteins of chromosomes put together

Chromatin condenses to form separate _______.

chromosomes 

Where is the nucleolus located?

Within the nucleus

What is the purpose of the nucleolus?

The site of rRNA synthesis

What are ribosomes made up of?

rRNA and protein

Where do ribosomes carry out protein synthesis?

In the cytosol (free ribosomes) and on the outside of the endoplasmic reticulum (ER) or near the nuclear envelope (bound ribosomes).

Endomembrane System

Regulates protein traffic and performs metabolic functions in the cell.

The endomembrane system consists of:

1. Nuclear envelope

2. ER

3. Golgi apparatus

4. Lysosomes

5. Vacuoles

6. Plasma membrane 

The components of the endomembrane system are either physically connected or connected by _____.

vesicles

The ER accounts for more than ____ of the total membrane in many eukaryotic cells.

half

The ER is _______ with the nuclear envelope.

continuous

What are the two distinct regions of ER

Smooth ER and Rough ER

What is the difference between smooth and rough ER?

Smooth ER lacks ribosomes whereas the surface of rough ER is studded with ribosomes.

Functions of smooth ER:

1. Synthesizes lipids

2. Metabolizes carbohydrates

3. Detoxifies drugs and poisons

4. Stores calcium ion

Functions of rough ER

1. Secretes glycoproteins

2. Distributes transport vesicles

3. Is a membrane factory for the cell

Glycoproteins

Proteins that have sugar molecules (carbohydrates) attached to them.

Transport Vesicles

Secretory proteins surrounded by membranes they are small membrane-bound sacs whose main job is to carry (transport) materials from one part of the cell to another.

Golgi Apparatus

The shipping and receiving center. Consists of flattened membranous sacs called cisternae. 

Functions of the Golgi apparatus:

1. Modifies products of the ER

2. Manufactures certain macromolecules

3. Sorts and packages materials into transport vesicles

Lysosomes

Digestive Compartments, a membranous sac of hydrolytic enzymes that can digest macromolecules. The clean-up crew of the cell.

In what environment do lysosomal enzymes work best?

In acidic environments with a pH of around 4.5-5.0

Where are lysosomal membranes and hydrolytic enzymes made?

In the rough ER

Hydrolytic Enzymes

Special proteins that speed up chemical reactions where molecules are broken down by adding water — a process called hydrolysis.

Phagocytosis

A process where a cell engulfs large particles (like bacteria or dead cells) by wrapping its membrane around them and bringing them inside in a vesicle called a phagosome.

Vacuoles

Storage containers for the cell, large vesicles derived from the ER and Golgi apparatus

What do vacuoles store?

Water, nutrients, and waste products,

How are food vacuoles formed?

By phagocytosis

Contractile Vacuoles

Special types of vacuoles found mainly in freshwater single-celled organisms like some protists.

Central vacuoles

A large, fluid-filled sac found mostly in plant cells. (A big water balloon inside the plant cell that also acts as a storage closet and waste disposal system.)

Mitochondria

The site of cellular respiration to make ATP, powerhouse of the cell.

Chloroplasts

Found in plants and algae, the sites of photosynthesis.

Peroxisomes

The cell’s detox center and fat-processing plant; small, membrane-bound organelles found in almost all eukaryotic cells.

Similarities between the mitochondria and chloroplast:

1. Enveloped by a double membrane

2. Contain free ribosomes and circular DNA

3. Grow and reproduce somewhat independently in cells

Endosymbiont Theory

The idea that some organelles in eukaryotic cells, like mitochondria and chloroplasts, originated from free-living bacteria that were engulfed by an ancestral host cell.

Cristae

The folds or inward projections of the inner membrane of the mitochondrion.

The inner membrane creates two compartments:

The intermembrane space and mitochondrial matrix

Mitochondrial Matrix

The innermost space inside the mitochondrion, enclosed by the inner membrane.

Where are the metabolic steps of cellular respiration catalyzed?

In the mitochondrial matrix.

Cristae present a large surface are for enzymes that synthesize ____.

ATP

Chloroplasts contain a ______ pigment.

green

Chloroplasts are found in:

leaves, algae, and other green plants.

Chloroplast structure includes:

Thylakoids, membranous sacs, stroma

Stroma

Like the cytoplasm but for the plant cells.

Thykaloids

Flattened, membrane-bound sacs inside the chloroplasts of plant cells. They are the site of the light-dependent reactions of photosynthesis.

The chloroplast is part of plant group organelles called _____.

plastids

Plastids

A family of plant cell organelles that are involved in making and storing important molecules.

Cytoskeleton

A network of fibers extending throughout the cytoplasm, the cell’s framework, conveyor belts, and muscles all in one.

Cytoskeleton functions:

Organizes the cell’s structures and activities, anchoring many organelles, supports the cell and maintains its shape.

The cytoskeleton is composed of three types of molecular structures:

1. Microtubules

2. Microfilaments

3. Intermediate filaments

Motor proteins 

Special proteins that “walk” or move along cytoskeleton fibers inside the cell. They carry cargo like organelles, vesicles, or molecules to different parts of the cell.

Microtubules

Thick, hollow tubes made of protein (specifically, tubulin), they are like the cell’s highways and structural beams.

Microfilaments

Microfilaments are the thinnest cytoskeleton fibers made of actin that help maintain cell shape, enable movement, and assist in cell division. Like thin ropes or cables that help the cell keep its shape and move.

intermediate filaments

Medium-thickness cytoskeleton fibers that provide mechanical strength and help maintain the cell’s shape and structural integrity. Like the steel cables in a suspension bridge.

Cilia

Short, hair-like projections that extend from the surface of some cells.

Flagella

Long, whip-like tail structures that extend from the surface of some cells.

How do microtubules affect flagella and cilia?

They control the beating of the flagella and cilia which differ in their beating patterns. 

Cilia and Flagella share a common structure:

1. A core of microtubules sheathed by the plasma membrane

2. A basal body which acts as an anchor

3. A motor protein called dyne which drives the bending movements

Basal Body

The organelle that anchors and organizes the microtubules of a cilium or flagellum at its base.

Dynein

A motor protein that “walks” along microtubules, moving cargo toward the cell center and powering the beating of cilia and flagella.

How does dynein “walking” move the flagella and cilia?

1. Dyeing arms alternately grab, move, and release the outer microtubules

2. Protein cross-line limit sliding

3. Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum

Cortex

A specialized layer of cytoplasm just beneath the plasma membrane that helps support the cell’s shape and enables movement.

Myosin

A motor protein that interacts with actin filaments (microfilaments) to produce muscle contraction and other types of cellular movement.

Pseudopodia

Temporary, arm-like projections of the cell membrane and cytoplasm that cells extend to move or engulf particles.

Cytoplasmic Streaming

A circular flow of cytoplasm within cells which speeds the distribution of materials within the cell.