The Cell - organisation

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Questions and Answers

What is the primary function of the nuclear envelope?

To direct metabolic activities.

To facilitate protein synthesis.

To store genetic material.

To regulate entry and exit of substances. (correct)

Which of the following activities is NOT directed by the nucleus?

Energy production. (correct)

Growth and metabolism.

Protein synthesis.

Cell division.

What are the main structural components of the plasma membrane?

A single layer of carbohydrates.

Three layers of cholesterol.

Two layers of phospholipids. (correct)

Single layer of proteins.

Which of the following correctly describes the nuclear envelope's relationship with the Endoplasmic Reticulum?

It has a double membrane that is continuous with the ER. Signup and view all the answers

What role does the nucleus play in protein synthesis?

It instructs the synthesis of proteins and ribosomes. Signup and view all the answers

What is the orientation of phospholipids in the plasma membrane?

Hydrophilic heads face outward and hydrophobic tails face inward. Signup and view all the answers

Which function is NOT performed by the proteins embedded in the plasma membrane?

Provide structural integrity to the membrane. Signup and view all the answers

What is the primary composition of cytoplasm?

A semi-transparent fluid mostly made of water with various solutes. Signup and view all the answers

What role do carbohydrate molecules play in the plasma membrane?

They provide immunological identity and can act as recognition sites. Signup and view all the answers

Which statement is true regarding the functions of membrane proteins?

Some membrane proteins act as enzymes and others as receptors. Signup and view all the answers

What is the main function of lysosomes in a cell?

To degrade proteins and membranes within the cell Signup and view all the answers

What process is facilitated by lysosomes to break down the cell's own components?

Autolysis Signup and view all the answers

How are lysosomes kept from destroying the cell contents?

By maintaining an inactive environment inside the lysosome Signup and view all the answers

What term describes the release of enzymes from lysosomes to break down other cells?

Exocytosis Signup and view all the answers

Which type of cells are likely to have abundant lysosomes due to their activity?

Leucocytes Signup and view all the answers

What is the primary function of peroxisomes in cells?

Breaking down fatty acids Signup and view all the answers

Which protein subunits make up the spindle fibres responsible for chromosome separation during mitosis?

Tubulin Signup and view all the answers

During which stage of mitosis do chromosomes align at the cell equator?

Metaphase Signup and view all the answers

What is the primary role of the structure formed by tubulin in flagella and cilia?

Cell locomotion Signup and view all the answers

What is the end result of the mitosis process?

Two genetically identical daughter nuclei Signup and view all the answers

What is the primary driving force behind active transport?

Chemical energy (ATP) Signup and view all the answers

During osmosis, what is the substance that typically moves across a semi-permeable membrane?

Water Signup and view all the answers

Which process describes the ingestion of large particles by a cell?

Phagocytosis Signup and view all the answers

What term describes the process of a cell 'drinking' and taking in liquids?

Pinocytosis Signup and view all the answers

What is the result when a substance moves from a high concentration to a low concentration without energy input?

Diffusion Signup and view all the answers

Which mechanism maintains homeostasis of sodium and potassium in cells?

Sodium-potassium pump Signup and view all the answers

What process is characterized by the removal of materials from a cell, such as waste products?

Exocytosis Signup and view all the answers

What is hyperplasia indicative of in tissues or organs?

Increased cell division Signup and view all the answers

Study Notes

The Nucleus

Largest feature in a cell
Bound by a double membrane, the outer layer is continuous with the Endoplasmic Reticulum (ER)
Pores in the membrane allow the passage of substances
Stores the genetic material (DNA)
Directs all metabolic activities of the cell, including growth, metabolism, protein synthesis, and reproduction (cell division)
Involved in cell division
Instructs the synthesis of proteins/ribosomes & RNA

Plasma (Cell) Membrane

Partially permeable
Made up of two layers
Consists of phospholipids (fatty substances) embedded with proteins & carbohydrate molecules

Phospholipids

Double layer (bilayer) of lipids, mostly phospholipids
Hydrophilic ("water-loving") at their phosphate ends - facing outwards
Hydrophobic ("water-fearing") along their lipid tail regions - orientated inwards

Plasma Membrane Structural Components

Some proteins are embedded in the bilayer, while others attach to the surface
Many proteins play a part in selective transport of substances across the membrane
Others act as surface receptors for substances such as hormones, or act as enzymes

Functions of Membrane & its Proteins

Contains cell contents
Regulate transport in and out of the cell
Provide immunological identity
Act as receptors (recognition sites) e.g. for hormones
Allows directed cell or organelle motility

Cytoplasm

Gelatinous, semi-transparent fluid that fills most cells and is where metabolic reactions occur
Mainly water, with many solutes including glucose, proteins, & ions
Contains many vital cellular chemicals e.g. in cell wall production by adding the carbohydrate part to the protein

Lysosomes

A secretory vesicle formed by the Golgi apparatus
Contain enzymes responsible for degrading proteins & membranes in the cell
Aids degradation of materials ingested by the cell due to hydrolytic (digestive) enzymes
These are kept apart from the cell, otherwise they would destroy the contents of the cell
Kept inactive by an alkaline environment within a lysosome
Abundant in cells with a phagocytic activity e.g. leucocytes

Lysosomes Functions

Digest materials which the cell consumed from the environment e.g. bacteria
Autophagy - the degradation of a cell's own components through lysosomal machinery
Autolysis - the destruction of a cell through the action of its own enzymes
Release enzymes outside the cell (exocytosis) in order to break down other cells

Recap

25 nm in diameter

Microtubules

Composed of subunits of the protein - tubulin
Form the spindle fibres for separating chromosomes during mitosis
Act as a scaffold to determine cell shape
When arranged in geometric patterns inside flagellae & cilia, they are used for locomotion

Peroxisome

A membrane-bound organelle
Contains oxidative enzymes such as catalase
A major function is the breakdown of fatty acids
Important in delaying cell ageing

Cell Division

Mitosis

Process by which a cell duplicates the chromosomes in its cell nucleus - in order to generate two genetically identical daughter nuclei (each containing 46 chromosomes)
The process of mitosis is complex and highly regulated

Mitosis Stages

Interphase
Prophase
Metaphase
Anaphase
Telophase

Diffusion

The process by which a substance moves from a region of high concentration to a region of low concentration
Rate of diffusion is variable: Concentration gradient, distance, the size of area, structure in path, & size of molecule

Osmosis

The passage of water down its concentration gradient towards equilibrium across a semi-permanent membrane
Occurs when solute molecules are too large to pass through the pores in the membrane by diffusion

Active Transport

The transport of substances up their concentration gradient i.e. from a lower to a higher concentration
Chemical energy (ATP) drives protein molecules in the membrane that transport substances across the membrane in either direction
E.g. the sodium-potassium pump maintains homeostasis of electrolytes sodium and potassium

Phagocytosis

The process by which the cell can obtain particles which are too large to be absorbed by diffusion or active transport

Pinocytosis

‘Cell drinking’ is very similar to phagocytosis except vesicles are produced called ‘pinocytotic vesicles’
Used for intake of liquids rather than solids
Both pinocytosis & phagocytosis are methods by which materials are taken into the cell in bulk – ENDOCYTOSIS
The reverse process materials are removed from the cell e.g. waste products – EXOCYTOSIS

Abnormal cell Growth

Hyperplasia

A term referring to the proliferation of cells within an organ or tissue beyond that which is ordinarily seen i.e. constant cell division

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Description

Cell Biology: The Nucleus and Plasma Membrane