bio

2.1 Why do we study cells?

1. Protect cells to prevent infection
2. Observe cells to identify and diagnose disease 

•  Malaria is a deadly disease that’s transmitted by mosquitoes

•  Vaccines have been created to protect human cells

•  Scientists need to learn about the cells that are infected and the organisms that cause malaria

3. Treat cells to heal illness

•  People with severe burns can be treated with skin grafts

• from other parts of the body

• Need information about skin and blood cells in order for this treatment to be possible

•  Doctors have been studying the cells of the heart

•  They have discovered that decreasing body temperature can help someone survive a heart attack

•  Cold temperatures reduce the harm to heart and brain cells

4.  Stop harming cells through our choices and actions

• Smoking can damage many of our body’s cells, but particularly those cells that make up lungs and respiratory passages

• Artificial sweeteners in pop disappoint brain cells that were expecting sugar based on taste. 

• Our brain tells us to keep eating so we can get the sugar we were promised

What is a cell?

• It’s the smallest unit of a living organism

• Has the following characteristics:

  1. A Lifespan

  2. Can grow, reproduce and repair themselves

  3. Can sense and respond to changes in their environment

  4. Require energy

  5. Produce waste

The Cell Theory

1.  All living things are composed of one or more cells

2. The cell is the most basic and functional unit of life

3.  All cells come from pre-existing
Cells

Cell Structure

Two main parts of a cell:

Organelles – a cell structure that has a specific function for the cell

Cytoplasm – Jelly-like liquid that contains many important substances and hold the organelles within a cell

CELL MEMBRANE

• Separates the inside of the cell from the outside environment

• Controls flow of materials in and out of the cell (semi-permeable)

• Flexible and Double layered

• Provides support for the cell

THE NUCLEUS

• Surrounded by a nuclear membrane (thin, double membrane that separates the nuclear contents from the cytoplasm) 

• The ‘control centre’ of the cell

• Directs the cells activities

• Contains genetic information (DNA)

CHROMOSOMES

• made up of chromatin—DNA

• chromatin coils up into chromosomes

• Thread-like structures in the nucleus

• Contain genetic information (hidden “message” cell reads)

MITOCHONDRIA

• The ‘power plant’

• Releases energy from glucose through process called cellular respiration

• Cells requiring more energy have more mitochondria

ENDOPLASMIC RETICULUM (ER)

• Canals and tubes connected to the nucleus

• Help transport materials within the cell

• Continuous from cell membrane to nuclear membrane 

important in production and release of hormones in the brain 

• Two types: Smooth ER and Rough ER

ENDOPLASMIC RETICULUM

Smooth ER

• Involved in production of fats

Rough ER

• Contains Ribosomes

• Involved in production of protein

RIBOSOMES

• Small organelles that make protein

• Required for all of cell’s activities

• They can be attached (to RER) or free-floating in the cytoplasm

GOLGI APPARATUS

• They sort and package proteins and other materials for transport out of the cell

• Create sac like structures called Vesicles that will travel outside of the cell

cells that secrete a lot of mucus such as the lining of intestines have many Golgi bodies  

VACUOLE

• Major functions include storage and support

• Membranous sac containing water, food and wastes

• animal cells may have many small vacuoles 

• plant cells usually have one large vacuole 

  • When filled with water it keeps the cells plump, which keeps the plants stems and leaves firm (called 

   keeping up turgor pressure)

Animal Organelle: LYSOSOME

• enzymes inside break down wastes

• Break down invading bacteria and damaged cell organelles 

Animal Organelle: CENTRIOLES

• Helps with cell division

Plant Organelle: CELL WALL

• An additional covering for plant cells outside of cell membrane

• Provides rigid shape, protection and structure for the cell

Plant Organelle: CHLOROPLAST

• Organelle that contains chlorophyll, the green pigment found in plants

• Site of photosynthesis – chlorophyll traps light energy 

2.3 The Importance of Cell Division 

• You started as a single cell: a fertilized egg.  Now your body is made up of trillions of cells.  Cell division allows organisms to reproduce, to grow, and to repair damage.

1. Cell Division for Reproduction 

• All cells use cell division to reproduce

• Asexual Reproduction 🡪 the process of producing offspring from only one parent; the production of offspring that are genetically identical to the one parent

  • Example: single-celled organism  (bacteria) and some multi-cellular organisms (houseleek) 

1. Cell Division for Reproduction 

• Sexual Reproduction 🡪 the process of producing offspring by the fusion of two gametes; the production of offspring that have genetic information from each parent 

  • These gamete cells are different from other body cells; they contain only half of the DNA usually found in a cell 

2. Cell Division for Growth 

• As multicellular organisms grow, the number of cells increases 

• Chemicals used during cell activity and growth enter the cell across the membrane and travel through the cell where they are used 

  • This process is known as diffusion (a transport mechanism for moving chemicals into and out of the cell, from an area of higher concentration to an area of lower concentration)

• Concentration 🡪 the amount of a substance present in a given volume of solution 

• Water enters and leaves cells by a process called osmosis (the movement of fluid, usually water, across a membrane toward an area of high solute (substance) concentration) 

• Diffusion and osmosis take time 

• Important chemicals must be available to all parts of a cell, in the right amount of water, for the cell to function properly 

• Waste products (e.g. carbon dioxide) must diffuse out of the cell quickly so they don’t poison the cell 

• When a cell gets too large, chemicals and water cannot move through the cell fast enough for the cell to use 

  • This is why cells grow in number and not in size, in order for an organism to grow 

3. Cell Division for Repair

• Every day your body sheds millions of dead skin cells, all of which are replaced by new ones 

• Your body replaces each red blood cell about every 120 days 

• If you break a bone, cells divide to heal the break 

• All organism need to repair themselves to stay alive

2.5 What is the cell cycle?

• Cell Cycle

  • The events in a cells life in which it is born, it grows, reproduces and dies

  • It is divided into two stages:

    • GROWTH STAGE🡪INTERPHASE

    • DIVISION STAGE 🡪 MITOSIS AND CYTOKINESIS

Why is Cell Division Important?

• Growth

• Maintenance:  the transfer of genetic information from the parent cell to the offspring

• Repair: replaces damaged or dead cells

• Reproduction

Division Stage 

• Mitosis – Contents of the nucleus (DNA) separate into two identical copies

• Mitosis has four phases: 

Prophase Metaphase Anaphase Telophase

INTERPHASE

• The cell grows, new organelles are made and DNA is duplicated

Stages of Interphase

G1 (Growth) Phase:

• the cell is growing and carrying out metabolic activities (eg. producing proteins)

S (Synthesis) Phase:

• the cell makes (synthesizes) an entire identical copy of its DNA.

G2 (Growth) Phase:

• the cell moves into its second growth phase where it approaches its maximum size and produces the structures needed for mitosis (cell division)

Interphase

• The cell spends almost 90% of its life growing

• Cell grows and carries out its normal functions

• Cell also makes copies of its organelles and DNA

MITOSIS:  Prophase

• Chromosomes coil and thicken

  • 2 sister chromatids held together by a centromere to make 1 chromosome

• Nuclear Membrane disappears

• Centrioles start to move to opposite poles

• Spindle fibres start to form

MITOSIS: Metaphase

• Centrioles are now located on opposite poles

• Spindle fibres attach to the centromere and align chromosomes at the centre of the cell

MITOSIS: Anaphase

• Chromosomes split

  • sister chromatids go towards opposite poles

MITOSIS: Telophase

• Nuclear membrane forms around the nucleus of each set

• Chromosomes stretch out and become thin (chromatin)

CYTOKINESIS

• Cytoplasm and other organelles are distributed amongst the 2 daughter cells

• Cell membrane forms around each new cell

CYTOKINESIS IN ANIMAL CELLS

In animal cells, the cell membrane pinches in the middle and creates a CLEAVAGE FURROW

CYTOKINESIS IN PLANT CELLS

In plant cells, a CELL PLATE is formed that develops into a new cell wall

Checkpoint in a Cell Cycle 

• During the cell cycle, the cell’s activities are controlled at specific points (checkpoints)

• At each checkpoint, specialized proteins monitor cell activities and send messages to the nucleus 

• The nucleus then instructs the cell whether or not to divide 

• A cell will remain in interphase if:

  • Signals from surrounding cells tell the cell not to divide

  • There are not enough nutrients for cell growth 

  • The DNA within the nucleus has not been replicated

  • DNA is damaged  

Life Span of  Cell 

• The cell cycle regulates how long a cell lives 

• Sometimes cells die because they have suffered injury or damage 

• Apoptosis 🡪 regulated or controlled cell death 

  • These cells are no longer useful 

  • It is a normal part of functioning of organisms 

  • For example: when your body fights an infection cells are produced to fight the virus.  Once the virus is removed from your body these cells are no longer needed and are removed via apoptosis 

2.7 Cell Division Gone Wrong: Cancer

• Cancer 🡪 a broad group of diseases that results in uncontrolled cell division

  • Due to a change in the DNA that controls the cell cycle

• One or more checkpoints fails, so the cell and all of its subsequent daughter cells continue to divide uncontrollably  

Cell Growth Rates and Cancer 

• A cancer cell is one that continues to divide despite messages from the nucleus and surrounding cells to stop growing and dividing 

• The uncontrolled growth and division may create a rapidly growing mass of cells that form a lump or tumour 

• Tumour 🡪 a mass of cells that continue to grow and divide without any obvious function in the body 

Cell Growth Rates and Cancer 

• The cells of the tumour may stay together and have no serious effect on surrounding tissues, other than physically crowding it  🡪 this is called a benign tumour

  • Cells in a benign tumour are NOT cancerous

• Malignant Tumour 🡪 a tumour that interferes with the functioning of surrounding cells; a cancerous tumour 

  • May interfere with the production of hormones or enzymes 

  • May destroy surrounding tissues 

  • Metastasis 🡪 the process of cancer cells breaking away from the original tumour and establishing  another tumour elsewhere in the body 

Comparing Benign and Malignant Tumours

Benign Tumour

• Encapsulated 

• Non-invasive

• Limited growth

• Doesn’t metastasize (spread to other parts)

• Rarely lethal 

Malignant Tumour

• Not-encapsulated

• Invasive

• Uncontrolled growth 

• May metastasize 

• Often lethal

Characteristics of Cancer Cells 

• Interferes with surrounding cells and disrupts their normal functioning 

  • Especially in normal division 

• Cancer cells can use up oxygen and nutrients, robbing normal cells of food 

• This can cause the healthy cells to stop replicating 

• Cancer cell growth can lead to the crowding of other cells in the body

Characteristics of Cancer Cells 

• Can divide isolated from others

• Cancer cells do not have a unique shape or carry out specialized functions 🡪 they are inefficient 

• Cancer cells use up energy and resources of other cells of the body to reproduce, but they do not do the same work as normal cells

Causes 

• When DNA is not replicated correctly, it leads to mutations  

• Mutations 🡪 a random change in the DNA

• Some mutations lead to the death of the cell or has a benign effect 

• ALL cancers are caused by a mutation in the genes that regulate cell division

• Once the cell cycle behaves abnormally, the cells may become cancerous and proliferate

• Carcinogens 🡪 any environmental factor that causes cancer 

• NOT all people exposed to a carcinogen will develop cancer 

• This is a major challenge for researchers because they cannot predict who will develop cancer 

• Examples of Carcinogens:  tobacco, asbestos, certain chemicals, some viruses (HPV, Hep B, leukemia), radioactivity, radiation such as X-ray and ultraviolet (UV) radiation

Screening

• Screening is especially important for people who have a family history of certain cancers (e.g. breast, colon)

  • You may choose to go through genetic screening 

• Screening is also beneficial to those who are exposed to carcinogens at work 

• Screening does NOT prevent cancer, but it does increase the chance of detecting cancer early enough to treat it 

• Examples

  • Self Examination 

  • Pap Test

  • Blood Test

• A Colonoscopy is a screening procedure with the aim of identifying abnormal growths along the colon wall

• A Mammogram is a type of X-Ray that is used to detect breast cancer. 

Confirming Cancer

• Biopsy: a doctor surgically removes a small portion of the suspected tumour to test it, which is then compared to normal cells.

Treatment

• The goal of cancer treatments is to slow down the growth of the tumours or destroy as many cancer cells as possible 

• Currently there are 3 main conventional ways:

1 Surgery 🡪 physically removing the cancerous tissue; usually preferred especially if tumour is well defined 

2 Chemotherapy 🡪 uses drugs to slow or stop cancer cells from dividing and spreading

•  Side effects may be hair loss, and nausea

• Usually the first step in cancer treatment (the aim is to shrink the tumour for surgical removal or radiation) 

3 Radiation 🡪 cancer cells are easily damaged by ionizing radiation (to stop the multiplication and division of cancer cells)

• Radiation is directed at the tumour