IB Biology HL cell biology

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cell theory

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cell theory

  1. all living things are composed of cells

  2. cells are the smallest unit of life

  3. cells come from pre-existing cells

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how do prokaryotic cells divide

binary fission

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how do eukaryotic cells divide

fission, mitosis, meiosis

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formula magnification

size of image / actual size of specimen

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formula image size

magnification * actual size of specimen

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formula actual size of specimen

size of image / magnification

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whats a stain for in wet mounts

a chemical that binds to structures (organelles) in the cell to see them more clearly

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how to find the FOV

use a metric/stage ruler (slide with ruler on it)

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estimate the size of a specimen

  1. estimate the fraction of the FOV the specimen occupies * FOV diameter

  2. FOV diameter / estimate how many times the specimen can fit into the FOV (lined up)

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pros of a compound light microscope (7)

  1. easy to use

  2. cheap

  3. dead and living cells observed

  4. color

  5. cell movement observed

  6. quick specimen prep

  7. no high voltage electricity neccessary

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cons of a compound light microsecope (2)

  1. low max mag (1500X)

  2. low resolving power

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pros of an electron microscope (2)

  1. high max mag (100,000X - 300,000X)

  2. high resolving power

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cons of an electron microscope (6)

  1. expensive

  2. dead cells only

  3. no movement observed

  4. no color without stain

  5. high voltage electricity required

  6. long specimen prep

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structures common to all cells (4)

  1. plasma membrane

  2. cytoplasm

  3. DNA

  4. Ribosomes ( euk = 80s pro - 70s)

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features of a eukaryotic cell

multi and uni cellular

has a nucleus

plants + animals

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features of a prokaryotic cell


no nucleus

bacteria + archaea

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prokaryotic cell structure (7)

  1. cell (plasma) membrane

  2. cytoplasm

  3. ribosomes

  4. cell wall

  5. pili*

  6. capsule*

  7. flagellum*

( * = in some, not all)

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function of cell (plasma) membrane

regulates what moves in/out of the cell

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function of cytoplasm

gel-like cytosol fluid inside with dissolved molecules such as lipids and fatty acids needed for metabolic reactions to keep the cell alive. (site of metabolic reactions

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function of ribosomes

build proteins during translation.

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function of cell wall

provides shape and allows the cell to withstand turgor pressure without bursting

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function of pili*

allows cell to attach to surfaces, swap DNA with other cells and harpoon DNA into the environment

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function of capsule*

stops cell from dehydrating and allows cell to adhere to surfaces

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function of flagellum*

long extensions on the cell allowing cell locomotion

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where can you find prokaryotic cell DNA

  1. Nucleoid

  2. plasmid

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prokaryotic nucleoid DNA

  • main DNA of the cell

  • free in the cytoplasm

  • single loop

  • naked = not wrapped around proteins

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prokaryotic plasmid DNA

  • extra pieces of DNA

  • circular + naked

  • smaller than main DNA

  • replicates independently of main DNA

  • not in all prokaryotic cells

  • can be shared between bacteria

  • often contains genes for antibiotic resistance

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binary fission

  • DNA is replicated semi-conservatively

  • the 2 DNA loops attach to the membrane

  • the membrane elongates and pinches off (cytokinesis) = 2 daughter cells

  • the 2 daughter cells are genetically identical

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membrane bound organelles (eukaryotic cells)

membrane is a barrier between aqueous solutions and is semi-permeable. the membrane creates compartments for the organelles with controlled conditions different for each organelle. (compartmentelization)

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eukaryotic cell structure (13)

  1. nucleus

  2. free + bound ribosomes

  3. rough ER

  4. smooth ER

  5. golgi apparatus

  6. vesicles

  7. lysosome

  8. mitochondria

  9. chloroplast

  10. vacuole

  11. microtubules + centrioles

  12. cytoskeleton

  13. cilli + flagella

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contains DNA which stores info for making proteins via translation + transcription

contains nucleolus - where ribosome sub units are made

has a double membrane with pores - allow eukaryotic cells to separate activities of gene translation + transcription

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catalyse synthesis of polypeptides during translation

have 2 sub units which come together

free = floating in cytoplasm - synthesising polypeptides used within the cell.

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rough endoplasmic reticulum

series of connected, flattened membrane sacs

play a central role in synthesis and transport of polypeptides

has bound ribosomes which synthesize the polypeptide and release it inside the rER

continuous with nuclear envelope which surrounds cells nucleus

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smooth endoplasmic reticulum

series of connected flattened membrane sacs that are continuous with the rER

locks ribosomes and not involved in protein synthesis

main functions - synthesis of phospholipids + cholesterol for formation and repair of membranes

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golgi apparatus

modifies polypeptides into their functional state

sorts, concentrates and packs proteins into vesicles

depending on the contents, vesicles are dispatched to 1 of 3 destinations

  1. within cell, to lysosomes

  2. plasma membrane of cell

  3. secretion to outside of cell via exocytosis

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membrane bound sacs containing and transporting materials within cells

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transport vesicles

move molecules between locations inside the cell by budding off 1 organelle compartment and fusing with another

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secretory vesicle

secrete molecules from cell via exocytosis. how new phosopholipids are added to the cell membrane

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small spherical organelles enclosed by single membrane. contain enzymes that work in oxygen poor areas and lower PH.

the enzymes digest large molecules and recycle components of the cells own organelles when they are old or damaged or if the cell is starving in the absence of nutrients.

also has an immune defense function - digests pathogens that have been engulfed by phagocytes.

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adapted for production of ATP by aerobic cellular respiration. surrounded by double membrane

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adapted for photosynthesis, captures light energy and uses it with water and carbon dioxide to produce glucose

inside are loght absorbing pigments (eg chlorophyll) which gives it its green color.

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mature plant cells have a central vacuole occupying 30%-90% volume of the cell for water storage.

its main role is to maintain turgor pressure against the cell wall so the plant stays upright

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cytoskeleton (not organelle)

helps maintain cell shape

organizes cell parts

enables cell to move and divide

several different components work together to form the cytoskeleton -

  • microtubules

  • actin filaments

  • intermediate filaments

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polymers of tubulin protein - forms part of cytoskeleton

used for intracellular transport of organelles and seperation of chromosomes during mitosis.

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paired cylindrical shaped organelles composed of groups of 3 microtubules organised with radial symmetry

functions -

arrangement of mitotic spindle during cell division

anchor points for microtubules in cytoplasm, cilia, flagella

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cilia and flagella

membrane bound extensions from cell surface, aiding in cell movement. formed when modified centrioles called a basal body.

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  1. metabolism

  2. response to stimuli

  3. homeostasis

  4. movement

  5. growth

  6. reproduction

  7. excretion

  8. nutrition

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animal cells

multicellular eukaryotes without a cell well

holozoic = eat other organisms with internal digestion of nutrients

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fungi cells

eukaryotes with chitin cell wall

uni/multi cellular

most are saprotrophs = secrete digestive enzymes into the environment then absorb the nutrients into their body after theres been external digestion.

some are parasitic

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plant cells

multicellular eukaryotes with cellulose cell wall

most are autotrophs - make their own food

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similarities in eukaryota cell structure (9)

  1. nucleus

  2. free and bound 80s ribosomes

  3. rER

  4. sER

  5. golgi apparatus

  6. vesicles

  7. lysosome

  8. mitochondria

  9. cytoskeleton

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differences in eukaryota cell structure

  1. plastids (plant)

  2. cell wall (fungi + plant)

  3. vacuoles (animal = small, temporary, expel exess water/waste)

    (fungi + plant = large, permanent water storage + pressure)

  4. centrioles (animal + plant)

  5. cilia + flagella (animal)

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atypical cell examples

red blood cells - atypical cells with no nucleus or mitochondria to create a higher surface area : volume ratio and thus have a more efficient gas exchange

aseptate fungal hyphae - multiple nuclei, no distinct individual cells

skeletal muscles - multiple nuclei, 1 large cell

phloem sieve tube element - no nucleus or organelles

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processes thought to have led to the origin of eularyotic cells

  1. infolding - ER, golgi apparatus, nuclear envelope

  2. endosymbiosis - mitochondria, chloroplasts

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inward folds of plasma membrane of ancestral prokaryotic cells. internal membranes allow the cell to carry out more complex chemical reactions in seperate compartments.

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evolved from small symbiotic prokaryotes that lived within other larger host cells.

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symbiotic ancestors of mitochondria (endosymbiosis)

maybe aerobic bacteria able to use oxygen in aerobic cellular respiration.

ancestral host call may have ingested some of these aerobic cells, instead of being digested they lived and respired in the cell.

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ancestors of cholorplasts (endosymbiosis)

maybe photosynthetic bacteria living in larger host cells. not digested but lived and photosynthesised in the cell.

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which evolved mitochondria or chloroplast

mitochondria because only some eukaryotes have chloroplasts.

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endosymbiosis supporting evidence

  1. mitochondria and chloroplast are a similar size to prokaryotic cells

  2. they have a double membrane = own cell membrane + membrane formed from being engulfed

  3. have 70s ribosomes

  4. circular naked DNA

  5. share common DNA sequences with prokaryotes

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all genetic info of an organism, same species share most of the genome, cells within an organism share a genome

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housekeeping genes

genes expressed in nearly all cell types

code for proteins associated with basic cellular functions

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process during development whereby newly formed cells become more specialized and distinct from one another as they mature.

occurs when different cell types express different genes

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gene expression

process by which the info encoded in a gene is turned into a function.

often a sequence of DNA is transcribed to form RNA, which is then translated to form a protein.

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non-housekeeping genes

differentially expressed in different cell types. some cell types express the gene, others dont

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how is differentiation in gene expression regulated

by proteins that bind to specific base sequences in DNA

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stem cells

able to specialize to become different cell types by differentially turning off some genes and activating others

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when does alot of differentiation occur

during embryonic development.

during differentiation of pluripotent cells, DNA methylation enables permanent slicing of some genes. at the same time, developmental genes begin to be expressed, differentiating the cells from eachother.

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hormons in gene expression

molecules produced in one cellular location in an organism, and whose effects are seen in another tissue/cell type

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mammal hormones

proteins or steroids

mammal hormones dont enter the cell but bind to receptors in the cell membrane and mediate gene expression through intermediate molecules

steroid hormones enter the cell and interact with steroid receptor proteins to control gene expression

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group of cells that have differentiated in the same way to perform the same function

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multicellular organisms composed of more than 1 cell their cells specialised and lose the ability to live independently

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  1. formation of cellular clusters from single cells

  2. differentiation of the cells within the cluster for specialised functions

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how cells may have formed clusters

a. group of independent cells come together

b. when unicellular organism divids, the daughter cell fails to seperate resulting in aggregate of identical cells

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selective pressure hypothesized to lead to multicellularity

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advantages of compartmentalisation (in cytoplasm of cells) (5)

  1. enhanced efficiency (easier control and no interference of other biochemicals)

  2. substances that can cause damage to components of a cell are kept inside the membrane of an organelle.

  3. conditions beneficial to a specific process can be created

  4. membranes and their organelles can be moved around the cell

  5. large surface area for processes that happen within or across membranes.

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regulate the transfer of molecules

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cell fractionation

method of spreading the sub cellular components so that the structures, functions, and molecular compositions of the isolated components can be studied. uses ultracentrifuges

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what can chromatography be used for (4)

  1. amino acids

  2. proteins

  3. carbohydrates

  4. plant pigments

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what can gel electrophoresis be used for (4)

nucleic acids

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advantage of post transcriptional modification of mRNA after transcription

avoids errors in translation that could be made/happening in the cytoplasm

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processes organelles in eukaryotic cells are involved in (4)

  1. producing energy

  2. metabolism

  3. biosynthesis

  4. degradation

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cellular respiration

the controlled release of energy from organic compounds in cells to form ATP

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aerobic respiration

  • takes place in the mitochondria

  • glucose + oxygen = carbon dioxide + water + ATP

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outer membrane mitochondria

forms a separate area within the cell creating the right conditions for cellular respiration to occur.

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inner membrane mitochondria

form cristae (folds) which increases the surface area meaning theres more space for anzymes involved in electron transport chain and oxidative phosphorylation

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inter membrane space mitochondria

small space allows for the rapid creation of a concentration gradient of hydrogen ions which is used to produce ATP

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matric mitochondria

fluid inside the mitochondria containing enzymes for cellular respiration, link reaction, krebs cycle. enzymes and their substrates concentrate together in a small volume of the matrix allowing faster reactions.

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photosynthesis chloroplast

production of carbon compounds in cells using light energy.

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double membrane chloroplast

forms a seperate area within the cell making the right conditions for photosynthesis. also determines what enters/leaves the chloroplast

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thylakoid membrane chloroplast

forms an extensive network of disc like structures in the chloroplast increasing the surface area.

attached to the membrane are photosystems containing chlorophyll molecules absorbing sunlight. the membrane also has other enzymes attached required in photosynthesis.

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thylakoid lumen chloroplast

small space in thylakoid discs with a small volume allowing for the rapid build up of hydrogen ions for a concentration gradient. used for production of ATP needed for photosynthesis.

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stroma chloroplast

fluid inside the chloroplast with enzymes for the calvin cycle (last step in process of photosynthesis). the enzymes and substrates are concentrated in the small area allowing for faster chemical reactions.

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nuclear membrane nucleus

has a double membrane allowing for bigger pores. bigger pores means its easier to break down and rebuild the nuclear envelope by farming vesicles during cell division.

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nuclear envelope nucleus

prevents ribosomes from reaching the RNA before its ready for use.

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nuclear pores nucleus

control what substances enter/exit the nucleus

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outer membrane nuclear envelope

continuous with ER and has the same function as rER

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inner membrane nuclear envelope

helps maintain shape and interacts with chromatin

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made of proteins and ribosomal RNA. function is to make proteins. has 2 units.

bottom small unit - holds mRNA in place

top large unit - has 3 sites to which tRNA attach. sites allow the correct amino acid to be attached to growing protein molecule

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free ribosomes

produce proteins for use inside of the cell

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