B2.3 Cell Specialization

differentiation

the transition from unspecialised cells into cells that have particular structures and functions

turn on and off certain genes

allows zygote to become different cells, organs, tissues etc.

selective gene expression

activating and selecting certain genes

function of selective gene expression

will perform different functions

morphogen gradients

the chemical signals used to "tell" stem cells what type of cells to become

transcription factors

encourage or discourage the transcription of certain genes

more transcription factors

more genes expressed

stem cells

undifferentiated cells which can divide endlessly and differentiate along different pathways

stem cell niches

micro-environment in the body which contain a large number of stem cells which can be used to maintain the number of stem cells or to promote their proliferation and differentiation

red bone marrow

contains stem cells which can be used to create all kinds of blood cells

hair follicles

sites containing stem cells

totipotent stem cells

can become any cells in embryo-adult

pluripotent stem cells

give rise to all adult cell lineages

multipotent stem cells

can give rise to multiple cell types within a lineage

early embryo stem cells

totipotent → become pluripotent relatively quickly

RBCs size

small to fit through narrow capillaries

neurons shape

long to reach throughout the body

sperm shape

long and narrow

egg shape

huge and rounded

white blood cells

grow when activated

surface area to volume ratio benefit

large surface area to volume ratio improves exchange

cell flattening

smaller volume → increases SA ratio

example of cell flattening

thylakoids & RBCs

microvilli

small projections inside a tube → increases SA

invagination

occurs when part of a cell folds back in on itself

kidneys structure

made of about 1 million nephrons which allow it to filter the blood

erythrocytes function

highly specialized cells whose main function is to carry oxygen, carbon dioxide and waste throughout the circulatory system

flattened erythrocytes

increased surface area for exchange & to fit through small blood vessels

type I pneumocytes form

large and narrow → increase SA for gas exchange; 95% of alveoli surface; thin → reduces distance for diffusion of gases

type I pneumocytes function

where gas exchange occurs

type II pneumocytes form

cubed shaped; less surface area; ~5% of alveoli surface; lots of organelles; secretary vesicles in cytoplasm → allows release of surfactant into alveolar lumen

type II pneumocytes function

produce surfactant to reduce sticking between type II pneumocytes

myofibrils

long contractile fibers made of proteins which allow a muscle to pull and move

cardiac muscle branching

branched → faster signal propagation between cells & three dimensional contraction

striated muscle branching

not branched → allows for uniform motion in one direction

cardiac muscle length

shorter due to the tension at which each muscle type must function; need to work across different distance

striated muscle length

shorter

cardiac muscle nuclei

one nucleus

striated muscle nuclei

multinucleate: fused individual cells with one membrane → to more effectively pull

spermatozoa function

transport the father's DNA to the ovum in the fallopian tube of the mother via vagina and uterus

acrosomes

includes enzymes to help it penetrate the ovum

sperm mitochondria

for energy

flagellum

locomotion

ovum function

provide the second half of the DNA for the zygote as well as all of the organelles the zygote will need

follicular cells corona radiata

provides energy

zona pellucida

blocks sperm entry

cortical granules

prevents polyspermy

zona pellucida after one sperm enters

locks down after one gets through

first division of zygote

first division is right after