SNC2D Grade 10 Academic Science Biology Cells, Genes, and Cancer

Thanks, Tony!

Biology: Chapter 1 Notes

 

Chapter 1.1—Studying the Structure of Cells

  • a cell is the smallest unit that can perform the functions of life
  • microscopes allows individuals to see cells, and this allowed the advancement of medicine (ex.: germs cause diseases)
  • microscopy is the science of using microscopes to view samples of objects
  • the nucleus is an organelle that controls the cell’s activities
    • typically the only organelle visible from a light microscope
    • there are 3 main parts to the nucleus:
      • the nucleolus: makes ribosomes (which help to make proteins)
      • nuclear membrane: protects the contents of the nucleus
      • nuclear pores: allow materials, such as ribosomes in and out of the nucleus
  • a micrograph is a photo taken with a microscope
  • the cell theory
    • all living organisms are made of one or more cells
    • the cell is the basic organizational unit of life
    • all cells come from pre-existing cells
  • the cytoplasm is the cytosol and organelles contained by the cell membrane (everything inside the cell membrane except the nucleus)
    • cytosol is the fluid material between the cell membrane and the nucleus
  • cells can have different functions (specialized cells—brain cell vs. muscle cell) but they still contain the same organelles
  • many organelles are related to proteins in some way (storage, production, transport etc.)
    • proteins allow cells to carry out life processes that keep you healthy; essential to growth and repair of body tissue
  • the organelles (specialized structure in a cell) found in cells are (either plant or animal; or both plant and animal)
    • cell membrane
      • separates the inside of the cell from the external environment (controls flow of materials into and out of the cell)
    • cytoplasm
      • includes the cytosol, the organelles and other life supporting materials (sugar, water etc.)
      • all contained by cell membrane (everything inside membrane; outside nucleus)
    • mitochondria (mitochondrion)
      • where energy is released from glucose to fuel cell activities
    • ribosomes
      • helps produce proteins (which make up much of a cell’s structure and are required for activities necessary for cell survival)
      • some ribosomes float in the cytoplasm, others are attached to E.R.
    • endoplasmic reticulum
      • a network of membrane-covered channels that transport materials made in the cell; is connected to the nucleus
    • vesicles 
      • membrane covered sacs that transport and/or store materials inside the cell
      • sometimes help these materials cross the cell membrane
    • Golgi body
      • sorts and packages proteins and other molecules for transport out of the cell
    • nucleus
      • controls all cell activities
    • vacuoles
      • contains water and other materials and are used to store/transport small molecules
      • plant cells tend to have one large vacuole; animal cells have several vacuoles
    • cytoskeleton
      • filaments and tubules that provide a framework for the cell (structure; “skeleton”)
      • provides tracks for vesicles and organelles to move on
    • cell wall (PLANT ONLY)
      • tough rigid structure lying just outside a plant cell’s membrane
      • provides structure for the cell
    • chloroplasts (PLANT ONLY)
      • trap energy from the sun to make glucose (glucose trapped is broken down in mitochondria to power cell activities)
    • lysosome (ANIMAL ONLY)
      • package of digestive enzymes that break down old/damaged organelles  and waste
  • cellular respiration occurs in all cells—changes glucose into energy
    • glucose + oxygen  =  carbon dioxide + water +energy

 

 

Chapter 1.2—Genes: Answers and Questions

  • the nucleus contains a master set of instructions that determines what each cell will become, how it will function, and how long it will live before being replaced
    • these instructions are carried in chromosomes—a thread like structure made mostly of DNA
  • every plant and animal species has a specific number of chromosomes in the nucleus of each cell
    • humans have 46 chromosomes (there are 23 types—1 from each parent)
  • in the cells of most plants and animals, chromosomes come in pairs—one of each pair comes from each parent when an egg and sperm unite
    • in humans, 23 from the mother, 23 from the father

 

 

  • chromosomes are made of a material called DNA (deoxyribonucleic acid)
    • each chromosome consists of a single molecule of DNA
  • DNA is the material found in the cell nucleus that contains genetic information
  • DNA is divided into segments, called genes
    • genes are segments of DNA that control protein production (the type of protein, and when they’re made), thus controlling the cell’s activities and structure
  • each rung of a DNA molecule, along with the piece of the ladder’s side to which the rung is attached, is a building block molecule
  • there are 4 types of building block molecules: A (adenine), C (cytosine), G (guanine), T (thymine)
    • the order in which the A, C, G, T building blocks are strung together, is called the genetic code (building blocks for DNA)
    • the genetic code is different for every individual (except identical twins)
  • a gene is a relatively small part of a DNA molecule—each DNA molecule consists of hundreds of thousands of genes
  • DNA controls many features, like hair and eye colour, and your ability to digest certain foods (lactose intolerant)
    • DNA controls this through genes, which control the type of proteins your cells can make
  • the job of genes is to control the manufacture of proteins
  • each protein is designed to do a specific job—some proteins help build parts of your body’ others carry materials throughout your body

 

 

  • DNA screening is the process of testing individuals to determine whether they have the gene or genes associated with certain genetic diseases
  • Down syndrome can be screened from a fetus—fluid is drawn from the amniotic sac; the fluid is isolated for cells, and a micrograph of the chromosomes in these cells is taken
    • doctors examine the chromosomes—someone with Down syndrome will have an extra chromosome
  • PKU is tested from a blood sample to detect the presence /absence of specific proteins in the blood
    • the presence/absence of a specific protein can indicate that the genes aren’t functioning correctly
  • Huntington’s disease can be detected by identifying the existence of a specific gene—if a person has this gene, 100% certainty they’ll develop Huntington (50% chance of getting disease if 1 parent has it)
    • ethical issues related to testing for Huntington—gives those who have it unnecessary pain (con); reduces stress of uncertainty for those at risk (pro)

 

 

  • the genetic code is universal—DNA building block molecules (A, T, C, G) produce the code for proteins in all types of organisms (bacteria, plants, animals)
  • if a particular gene could be transferred between two different types of organisms, one species could then make proteins usually made only by the other species
  • transgenic organisms are organisms whose genetic information has been altered with the insertion of genes from another species
  • transgenic organisms are known very little for their long term consequences
    • how do GMO (plants) affect the consumers of it (humans)
    • is transplanting organs from transgenic animals (pigs) a good idea—spread viruses pigs are immune to, into humans

 

 

  • cloning is the process of creating identical genetic copies of an organism
  • for example, taking a part of a plant, rooting it, and therefore producing more plants that are exact copies of the parent plant

 

 

  • a mutation is the change in the DNA of an organism
  • because genes code for specific proteins based on the order of the DNA building blocks, a change in the order of A, T, C, G is known as mutation
  • mutations alter the structure of the protein it produces
    • it alters how well the protein can do its job
    • example: those who have sickle cell anemia have a mutation in the gene that codes for haemoglobin protein in the blood, this causing abnormal functions of the blood and red blood cell
  • mutations are caused by mutagens—substances/factors that cause a DNA mutation (damages DNA)
    • example: sun’s UV rays, x-ray, chemicals (mercury)
  • a mutation occurs, when the sequence of A, T, C, G building blocks change
  • not all mutations are harmful
    • a mutation that occurs on the non-genetic part of the DNA molecule isn’t harmful
    • even mutations that change proteins, aren’t 100% of the time harmful
  • gene mutations are partly to blame for some diseases
    • gene therapy corrects faulty genes—not much success though

 

 

Chapter 1.3—Cells from Cells

  • cell reproduction is the process by which new cells are formed
  • cell reproduction and the reproduction of a multicellular organism is different
    • in cells, one parent creates 2 daughter cells (that are identical in genes)
    • in multicellular organisms, 2 organisms create 1 baby (don’t contain identical genes to both parents)

 

  • cell division is the process by which a parent cell divides into 2 daughter cells
  • for single celled organisms, cell division is the main process by which individuals reproduce
  • in multicellular organisms, cell division is the process by which a fertilized egg becomes an adult with millions of cells

 

 

  • cell division also occurs when cells become too large to perform efficiently the functions of survival
  • the cell membrane plays a significant role in a cell’s functions of survival
    • molecules of food and oxygen get delivered to every cell in your body, and enter the cell through its membrane (process known as diffusion)
  • cell membrane is a barrier which everything must pass on its way into or out of the cell
  • diffusion is the movement of molecules from areas of high concentration to low concentration
  • the diffusion of water is known as osmosis
  • the cell membrane is selectively permeable—allows certain substances to go through, and rejects certain substances from going through

 

 

  • the surface of the cell must be big enough to allow for the entry of all of the oxygen and nutrients needed by the cell’s organelles, nucleus, and cytosol
  • as cells use these nutrients, they become bigger (more volume)
  • a cell needs enough surface area to service its volume
    • as a cell become larger, the surface area to volume ratio decreases
  • a cell can’t be too big, or else it will not have enough surface area for the passage of all the nutrients it needs and the wastes it produces
    • therefore, when a cell reaches a certain size, it must divide to produce smaller cells (which have a higher SA:V ratio)

 

 

  • you can’t divide a cell simply by cutting it down the middle to form daughter cells
    • what would happen if the nucleus wasn’t exactly in the centre of the cell
    • there would be an uneven amount of chromosomes in the daughter cells
  • there are 2 main parts to cell division:
    • mitosis: the process by which the duplicated contents of the cell’s nucleus divide into 2 equal parts
    • cytokinesis: the separation of the 2 nuclei and cell contents into 2 daughter cells

 

 

  • all cells need to have the exact same genes (ALL 46 in a human) in order to function correctly, and produce the required proteins
    • therefore, the parent cell can’t just divide its chromosomes into 2—this would mean each daughter cell would have half the required chromosomes needed to survive
  • a parent cell makes a copy of every chromosome before it divides—it gives one copy to each of the 2 daughters
  • the copying process is called DNA replication—the process by which DNA is copied, creating sister chromatids joined at the centromere
    • during replication, the two copies remain attached to each other by the centromere
  • until the cell gets ready to divide, chromosomes are normally long and loose threads
    • just before cell division, the chromosomes become thicker and bulgy
  • at roughly the same time as DNA replication, the centrosome organelle doubles (cell has 2 copies)
    • centrosome help organize the tubules that make up cytoskeleton

 

 

  • mitosis has 4 phases:
    • PROPHASE
      • replicated chromosomes coil in various ways until they are finally condensed (short) and thick
      • membrane around nucleus begins to break down; nucleolus disappears
      • the two centrosomes/centrioles (not centromere) head toward the opposite ends of the cell
      • extending from the centrosomes are spindle fibres (microtubules) towards the centromeres of the sister chromatids
    • METAPHASE
      • longest phase of mitosis
      • centrosomes reach the opposite ends of the cell and the chromosomes move towards the middle of the cell
      • eventually all chromosomes line up along the centre of the cell
      • each centromere becomes attached to two spindle fibres—one from each centrosome
    • ANAPHASE
      • shortest phase
      • the proteins holding the two chromatids together at the centromere break apart
      • the spindle fibres pull one of the sister chromatids towards each of the poles (once chromatids separate, they become chromosomes)
      • the cell has twice as many chromosomes as usual at this point
    • TELOPHASE
      • the spindle fibres start to disappear
      • membranes form around the 2 new daughter nuclei—one at the end of each cell
      • within each nucleus, a nucleolus appears
      • chromosomes become less coiled and harder to see (longer and thinner)

 

 

  • cytokinesis occurs after mitosis
  • the division of the rest of the cell (the cytosol and organelles) usually begin before telophase is complete
  • cytokinesis is different between plant and animal cells
    • ANIMAL CELL
      • a ring of specialized proteins around the middle of the cell starts to contract
      • the contraction pinches the cell membrane until the parent cell is divided into 2 parts
      • each daughter cell has a complete set of chromosomes in a nucleus and its own share of cytosol and organelles
    • PLANT CELL
      • the rigid cell wall makes it necessary for cytokinesis to be different in plants than animals
      • the Golgi body starts to produce small vesicles—each vesicle contains materials needed to form a cell wall (a structure that helps to form the cell wall in the process of plant cell cytokinesis)
      • the vesicles line up between the two new nuclei forming a cell plate—it grows outward and joins the old cell wall
      • new cell walls are secreted on each side of the cell plate, dividing cytoplasm in 2
      • the new membrane forms inside the cell walls

 

 

Chapter 1.4—The Cell Cycle 

  • the lifespan of different cells varies
    • some cells live a rough life (exposed to constant abrasion and toxins) meaning they need to be replaced more
    • stomach(2 days)  and skin cells (20 days) are replaced the most frequently
  • some cells are encouraged to divide, while others are encouraged to “stay as they are”
    • molecules/proteins carry signals in cells, sharing info about when the cell should divide

 

 

  • there are 2 main phases in a cell cycle
    • interphase
      • periods of growth in the life of a cell; consists of 2 growth stages (more organelles, cell grows larger or else it would be smaller and smaller), and a DNA replication stage (aka synthesis; forms sister chromatids)
    • cell division
      • mitosis and cytokinesis

 

 

  • cell cycle checkpoint is a point in the cell cycle when proteins determine whether cell division should or should not occur
  • there are 3 main points when a cell checks itself:
    • before DNA replication—does cell have enough nutrients to support growth
    • before mitosis—has the DNA replicated
    • before cytokinesis—has mitosis occurred correctly; are there normal amounts of chromosomes in the nuclei
      • very important—many cells leave the cycle at this point, as often, more cells of that type aren’t needed (body doesn’t need cell to divide—they enter a non-dividing stage; most cells in human body are at this stage)
  • when cells leave cycle, they become non dividing—carries out its functions until death
    • they can leave cycle in order to die also
  • cell division won’t occur if:
    • there aren’t enough nutrients to support cell growth
    • DNA hasn’t replicated
    • DNA is damaged

 

 

  • some cells leave cycle to die (damaged beyond repair for example); the contents of cell leaks out irritating surrounding cells
  • some cells die through suicide—a cell breaks down in an organized way
    • its contents are packaged and distributed for use in other cells
    • suicide is pre-programmed into a cell through its proteins from suicide genes
    • cells kill themselves in certain situations—for example, when cell survival is a threat to organism (cell infected with a virus)
      • proteins of cell kill it (protein from suicide genes)
    • cell suicide is how fingers form

 

 

  • cancer is when cells with abnormal genetic material divide uncontrollably and can spread to other body parts
  • some cells are transformed so that they ignore the checkpoints in the cell cycle
    • instead of leaving cycle to die, they divide repeatedly and excessively, forming a clump of cells (tumour)
    • a tumour is an abnormal clump/group of cells
  • the abnormal cells, with further mutation, can become cancer
    • cancer is cells with abnormal genetic material that are dividing uncontrollably and can spread to other body parts and continue dividing uncontrollably there
  • cancer can be spread through the body by blood, and continue dividing there
  • normal cells can undergo 20-30 rounds of cell division—any more may result in mutated cells
    • after 20-30 rounds, the cell commits suicide
    • in cancer cells, enzymes cause cells to be unaware of the need to commit suicide or make it impossible to commit suicide
  • most cells stop dividing when they realize they’re not attached to surface; cancer cell doesn’t do that
  • carcinogens are mutagens which cause cancer
    • asbestos, tobacco smoke etc.
  • abnormal cells take up space from normal cells (they take nutrients away from normal cells)
    • tumours reduce effectiveness of other cells’ cancer cells usually have several mutations before control of cell division is lost

 

 

Handouts and Slideshows

  • prokaryotes vs. eukaryotes
    • eukaryotes have a membrane bound nucleus; prokaryotes don’t

 

  • proteins
    • ribosomes make proteins
    • proteins enter E.R. for modification
    • E.R. packages proteins into vesicles
    • vesicles transport/carry protein to other organelles or the Golgi apparatus
    • Golgi uses vesicles to export proteins out of the cell

 

  • animal cells have Lysosome, many vacuoles, and centrioles—plant cells don’t
  • plant cell has cell wall, chloroplasts, one vacuole—animal cells don’t
    • cell wall provides structural support and prevents cell rupture (located outside cell membrane)
  • central vacuole for plants controls “turgor pressure”

 

  • cells need to divide because:
    • to reproduce (single-celled organisms)
    • to grow (make new cells)
    • to repair (to replace old or damaged cells)

 

 

  • DNA has instructions that determine what each cell will become, how it will function, and how long it will live before being replaced
  • each cell in a human body has 23 different chromosomes—there are 2 versions of each chromosome (one from each parent)
  • each chromosome is a single molecule of DNA
  • DNA is in the shape of a double helix
  • genes code for 1 (or more ) protein
  • DNA has 2 main parts:
    • the sugar-phosphate backbone (handrails)
    • nitrogen bases (rungs/steps of ladder—A-T, C-G)
  • functions of proteins
    • structure
    • enzymes (make chemical reactions in body happen faster)
    • antibodies (immune system)
    • hormones
    • transport (of molecules)
    • contractile (help muscles contract for movement)

 

  • a typical cell spends ¾ of cell cycle preparing for division
  • mitosis is the process by which all cells except sex cells divide
  • purpose of mitosis is to divide up DNA that has been copied and create two identical cells

 

  • cytokinesis is the division of the cytoplasm; mitosis is the division of the nucleus
  • all cells go through mitosis; all cells need to grow larger and repair old cells

 

  • many cells leave cell cycle after mitosis (don’t need more cells of that type)
    • when cells leave the cell cycle, they become non-dividing
    • most cells in human body are non-dividing (muscle and nerve cells for example)
  • if cells don’t get change to grow, they become smaller (eventually too small to function correctly)

 

  • cancer is when cells have abnormal genetic material that are dividing uncontrollably and can spread to other body parts
    • cancer cells ignore the “stop signs” in the cell cycle, and divide repeatedly and excessively
    • cancer cells can’t stop dividing, don’t stick to surfaces or to other cells, doesn’t self-destruct, don’t specialize
    • cancer is when DNA is damaged
      • DNA is damaged through mutations (especially if damage is in regions that produce checkpoints/suicide proteins
      • DNA mutations are caused by carcinogens (tobacco, radiation, toxins, viruses like HPV, inherited from parents etc.)
    • benign is a slow-growing/non-growing tumour that doesn’t spread; malignant is a fast-growing tumour that can spread easily through body (through blood)
    • cancer cells take nutrients from normal cells
    • prevention (avoid carcinogens), early diagnosis (annual checkups), and treatment (surgery, radiation, chemo)
    • as we age, risk of cancer increases (weaker immune system, health complications, more likely DNA damaged)
    • family history is a factor but not a definite for getting cancer