IB BIOLOGY TOPIC 1

cell theory

- all living things are composed of cells
- the cell is the smallest unit of life
- cells only arise from pre-existing cells

challenges to the cell theory

- striated muscle challenges the idea that a cell has one nucleus
- giant algae challenges the idea that cells must be simple in structure & small in size
- aseptate fungal hyphae challenges the idea that a cell is a single unit

functions of life

- metabolism
- response
- homeostasis
- growth
- reproduction
- excretion
- nutrition

explain why small cells are more efficient than big cells

- larger surface area to volume ratio can act more efficiently
- diffusion pathways are shorter (takes less time & energy)
- concentration gradients are easier to generate

advantages of cells differentiating

- makes it possible to complete functions that individual cells can't do alone
- functions are performed faster
- the cell uses less energy because they only have to do one specific job

describe how new formed cells become specialized

Newly form cells get signals that tell them to deactivate (or activate) certain genes. Active genes are packages in an expanded form while inactive genes are condensed.

how many different distinct highly specialized cell types have been recognized by humans?

220

stem cell

is an unspecialized cell that can continuously divide & replicate, & have the ability to differientate into specialized cell types

totipotent

can differentiate into any type of cell
(ex: first divisions of embryonic stem cells)

pluripotent

can differentiate into many types of cells
(ex: embryonic stem cells)

multipotent

can differentiate into a few closely-related types of cell
(ex: adult stem cells, cord blood stem cell)

unipotent

can generate but only differentiate into their associated cell type
(ex: skin cell)

Stargardt's macular dystrophy

problem: causes progressive & eventually total loss of central vision
treatment: embryonic stem cells are treated to become retinal cells, & retinal cells are injected into the retina
benefit: stem cells are currently the only viable treatment for this condition

therapeutic cloning

for
- may lead to discoveries, beneficial technologies, cures
- transplants are less likely to be rejected
- does not require death of another human being

against
- involves destruction of human embryos
- embryonic cells may develop into cancerous cells
- alternative technologies may fulfill similar roles
- religious/moral objections

magnification

drawing size ÷ actual size

actual size

drawing size ÷ magnification

drawing size

actual size × magnification

resolution

the shortest distance between two points that can be distinguished

explain why electron microscopes have a better resolution than light microscopes

electrons have a shorter wavelength

ultrastructure

all the structures of a biological specimen that are at least 0.1 nm in their actual dimension

what's one thing that electron microscopes can see, but light microscopes cannot

viruses

prokaryote

a single-celled organism that doesn't have a distinct nucleus with a membrane or specialized orgnanelles

binary fission (process)

- DNA is replicated semi-conservatively
- 2 DNA loops attach to the membrane
- membrane elongates & pinches off

eukaryote

a cell which DNA is in the form of chromosomes contained within a distinct nucleus

benefits of compartmentalization

- efficiency of metabolism
- localized conditions
- toxic/damaging substances can be isolated

cell wall

protects the cells, maintains its shape, & prevents excessive water uptake

plasma membrane

nucleus

- contains genetic info
- mRNA is transcribed here

mitochondrion

- site of ATP production
- powerhouse of the cell

free ribosomes

synthesizes proteins to function in the cytoplasm

rough endoplasmic reticulum

synthesizes proteins which are to be transported to the Golgi for modification before secretion outside the cell

Golgi apparatus

- processes/modifies proteins from the rER

vesicles

- transport materials inside the cell
- proteins are repackaged here

lysosomes

break down ingested food in vesicles, unwanted/damaged organelles, & the cell itself

vacuoles

absorb & digest food

flagellum

used to move the cell

cilia

used to either move the cell or move the fluids next to the cell

microtubules & centrioles

- part of the structure of flagella
- role in cell division

chloroplast

site of photosynthesis

cytoplasm

is made of water, proteins, salt & sugar

disproving Davson-Daniella Model

- freeze-etched micrographs (freezing & fracturing cells ➟ showed globular structures scattered in the center of the membrane)
- protein extraction (proteins varied in size & were globular ➟ unfit to form on surface of the membrane)
- fluorescent antibody tagging (markers are attached to antibodies that bind to membrane proteins ➟ cells fuse together ➟ red & green markers are mixed)

general functions of membrane

- sites of hormone-binding
- enzymatic action
- cell adhesion
- cell-to-cell communication
- channels for passive transport
- pumps for active transport

phospholipid bilayer

- composed of glycerol
- hydrophobic & hydrophilic regions cause the phospholipids to align as a bilayer if there is water present

cholesterol

helps regulate membrane fluidity/flexibility & is important for membrane stability

integral proteins

= membrane proteins
- control the entry & removal of specific molecules from the cell

transport proteins

go all the way through the bilayer

peripheral proteins

remain bound to the surface of the membrane & are often anchored to an integral protein

glycoproteins

are composed of carbohydrate chains attached to peripheral proteins
- plays a role in recognition of like-cells
- involved in immune responses

passive transports

occurs in high-to-low concentrations
- movement occurs along the concentration gradient

diffusion

substances move between phospholipd molecules/proteins that possess channels

facilitated diffusion

non-channel protein carriers change shape to allow movement of substances other than water

osmosis

the diffusion of water

isotonic

equal concentration of solute
- cell has normal shape

hypertonic

lesser concentration of solute
- cell shrinks

hypotonic

higher concentration of solute
- cell can burst from being too big

active transport

requires ATP; involves the movement of substances against a concentration gradient
- allows cell to maintain different interior & exterior concentrations

sodium-potassium pump

endocytosis

allows macromolecules to enter the cell
- portion of plasma membrane is pinched off to enclose macromolecules ➟ formation of a vesicle

exocytosis

allows molecules to leave

describe how the plasma membrane breaks & reforms during exocytosis & endocytosis.

1. vesicle approaches plasma membrane
2. membrane fuses
3. there's a single phospholipid bilayer at the point of contact (temporary)
4. membrane pore opens ➟ allows content to pass through

phagocytosis

intake of food/solids

pinocytosis

intake of liquids

primary active transport

direct ATP

secondary active transport

energy is derived from built up concentration from previous ATP

binary fission

cell cycle

all stages in the life cycle of a cell

interphase

composed of G1, S, & G2
- by the end of interphase, an individual cell has two full sets of DNA/chromosomes, & is large enough to divide

G1

- DNA transcription
- protein synthesis (centrioles)
- cell respiration (produces energy)
- growth of cell volume
- organelles double (mitochondria & chloroplast)
- increase in energy stored

G0

the stage where cells are unlikely to divide (ex: neurons)

S

- synthesis of genetic material
- DNA replication
- duplication of chromosomes into sister chromatids

G2

- growth & production of components needed for cell division (mitosis & cytokinesis)

3 metabolic reactions that occur during interphase

- protein synthesis
- DNA replication
- increase in the number of mitochondria and/or chloroplast

mitosis

= nuclear division;
split into 4 parts: prophase, metaphase, anaphase, & telaphase

prophase

- DNA and proteins condense into tightly coiled chromosomes (& become 2 sister chromatids)
- nuclear envelope breaks down
- centrioles begin to move to opposite poles
- spindle fibers form between 2 centrosomes
- chromosomes become attached to the spindle fibers at their centromeres

metaphase

- spindle fibers attach to each chromosome
- chromosomes align at the equator

anaphase

- centromeres divide
- sister chromatids separate to opposite sides of the cell
- spindle fibers begin to shorten

telophase

- nuclear membrane starts to form
- chromosomes begin to uncoil
- the spindle fibers fall apart

4 processes involving division by mitosis

- growth
- asexual reproduction
- tissue repair
- embryonic development

cytokinesis

division of cytoplasm

cytokinesis in plant & animal cells

plant: vesicles containing cell wall material line up between two nuclei. they form a cell plate, which then forms a new cell wall & create daughter cells

animal: animal cells form a cleavage furrow

apoptosis

the death of cells which occurs as a normal & controlled part of an organism's growth/development

cyclin

= a family of proteins that control the cell cycle
- bind & activate cyclin dependent kinase enzymes (CDKs)
- cyclin proteins appear at different stages & help regulate cell cycle

roles of the four cyclins involved in control of the cell cycle

cyclin A, D, & E: induce DNA replication, centrosome duplication & spindle fiber apparatus formation

cyclin B: controls mitotic spindle formation & alignment of sister chromatids

diploid

(of a cell/nucleus) containing 2 complete sets of chromosomes, 1 from each parent

haploid

(of cell/nucleus) having a single set of unpaired chromosomes

chromatin v. chromosomes v. chromatids

chromatin: the loose combination of DNA & proteins

chromosomes: are made up of a pair of chromatids

chromatids: each of the two thread-like strands into which a chromosome divides during cell division. each contains a double helix of DNA

explain why cells need to supercoil their DNA molecules.

cells need to super coil because it results in condensed structures called sister chromatids.
- to become more organized

outline how DNA molecules are supercoiled

1. DNA is wrapped around special protein molecules called histones combined loop of DNA and protein is called nuclear zone
2. nucleosones are packaged into a thread. end results is a fiber knows as chromatin.
3. fiber is looped and coiled yet again
4. leading finally to familiar shape of chromosomes. chromosomes are not always present, only when the nucleus is about to divide.

centromere

a region of condensed chromosome that looks pinched

telomere

the end of DNA molecule
- prevents chromosomes from accidentally attaching to each other

histones

protein that organizes chromosomes and around which DNA wraps

tumor

a mass of unspecialized cells that pile up because of abnormal growth

cancer

malignant tumor; a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body

ancogenes

- signals for what the cells need to do (growth)
- can become cancerous after mutating ➟ if this occurs, apoptosis does not happen & the cells keep reproducing uncontrollably

proto-oncogenes & tumor-suppressor genes

proto-oncogenes: start cell division

tumor-suppressor genes: switch off cell division

oncogenes

genes that lead to controllable cell division

mutagens

agents that cause gene mutations

mutation

a change in an organisms genetic code. a mutation/change in the base sequence of a certain genes can result in cancer

carcinogens (& examples)

chemicals that cause mutations

ex: ultraviolet radiation, x-rays, & gamma rays

what factors (other than exposure to mutagens) increase the probability of tumor development in humans?

- late detection
- low immune system
- environmental influence
- life span
- size
- lifestyle choices
- heredity