CELL AND MOLECULAR BIOLOGY

Cellular Biology, Metabolism

cell theory

17th century, microscope developments, 5 main points:

• all living things are composed of cells

• the cell is the basic functional unit of life

• the chemical reactions of life take place inside the cell

• cells arise only from pre-existing cells

• cells carry genetic information in the form of DNA, shich is passed from parent cell to daughter cells

six kingdoms of living things

bacteria, archaea, protista, plantae, animalia, fungi

two main cell types

eukaryotic and prokaryotic

eukaryotes

possess membrane bound organelles (eg. nucleus, mitochondria, etc.),

prokaryotes

no nuclei or membrane bound organelles

possess a cell membrane, cytoplasm, genetic material and ribosomes

DNA is organized into small circular chromosomes located inn a region of the cell termed the nucleoid

cell membrane

semipermeable barrier that regulates the passage of materials into and out of the cell

small and nonpolar molecules can pass (eg. H₂O, O₂), large, polar, charged molecules cannot (use carrier proteins instead)

fluid mosaic model

model of the cell membrane, consists of a phospholipid bilayer with proteins embedded throughout, the membrane is asymmetrical, lipids and many of the proteins can move freely/dynamically within the membrane

phospholipid bilayer

long, nonpolar hydrocarbon chains are inside the bilayer, and phosphorus-containing, polar, hydrophilic heads face outwards

nucleus

contains DNA wound around structural proteins called histones

DNA can tighten or loosen itself with the histones

where transcription and ribosomal RNA synthesis occurs

ribosome

facilitate protein production and are made of two rRNA sequences (ribosomal subunits), either unbound or bound to the rough ER

endoplasmic reticulum

network of membrane enclosed spaces involved in the transport of materials throughout the cell, both smooth and rough ER

rough ER

contains ribosomes, protein production

smooth ER

does not contain ribosomes and is involved with metabolism and the production of lipids

golgi apparatus

cellular trafficking, receives proteins and lipids from the smooth ER, modifies and repackages into vesicles, distributes them to various destinations within or outside the cell (exocytosis)

mitochondria

sites of aerobic respiration, convert sugars, fats into ATP, inner and outer membranes with an intermembrane space

also has own genome, divides by binary fission, independently of the nucleus

cytoplasm

includes the cytosol and the cell’s organelles

cytosol

cellular fluid contained within the cell membrane

cyclosis

transport within the cytoplasm, streaming movement within the cell

vacuoles

a type of vesicle, found in both plants and animal cells

animal cell vacuoles

smaller, used as transport vesicles for exocytosis and endocytosis, used for storage of water and minerals

plant cell vacuoles

usually one central vacuole for support and structure, used for storage of water and minerals

centrioles

only found in animal cells, composed of microtubules and involved in spindle organization during cell division, not bound by membranes

centrosome

a pair of centrioles oriented at right angles with each other, organizes microtubules and helps regulate the progression of the cell cycle

lysosome

membrane bound vesicles that contain hydrolytic enzymes, breaks down materials ingested by the cell

autolysis

an injured or dying cell may self-destruct by rupturing lysosome membranes to release hydrolytic enzymes

cytoskeleton

supports the cell, maintains its shape and aids in cell motility, composed of microtubules, microfilaments, and intermediate filaments

microtubules

hollow rods made of polymerized tubulin, framework for organelle movement

cilia and flagella

specialized arrangements of microtubules that extend from certain cells and are involved in cell motility and cytoplasmic movement

microfilaments

solid rods of actin, for cell movement and support, muscle contraction (actin and myosin), move materials across the plasma membrane

intermediate filaments

a diverse group of filamentous proteins (eg. keratin), structural backbone of the cell, withstand tension, makes the cell structure more rigid, anchor organelles

simple diffusion

net movement of dissolved particles down their concentration gradients, no energy required

osmosis

simple diffusion of water, water moves from areas of lower solute concentration to higher solute concentration (to reach isotonic solutions)

facilitated diffusion

the net movement of particles down their concentration gradient with the use of a channel or carrier protein, does not require energy

active transport

the net movement of particles against their concentration gradients with transport proteins and external energy

symporters

active transporter, moves two or more ions or molecules in the same direction across the membrane - one moves with its gradient, one moves against

antiporters

exchange one or more ions or molecules with another across the membrane, molecules move in opposite directions - one moves with its gradient, one moves against

pumps

energy-dependent carriers, require ATP, eg. sodium-potassium pump

endocytosis

cell membrane invaginates, forming a vesicle that contains extracellular material

triggered by the binding of particles on the cell membrane receptors

pinocytosis

ingestion of fluids or small particles

phagocytosis

engulfing of large particles

exocytosis

a vesicle within the cell fuses with the cell membrane, releasing contents to the outside

cell growth and intercellular signaling, eg. neurotransmitters

cell division

a means of reproduction (unicellular) or growth and development (multicellular), cell doubles its organelles and cytoplasm

interphase

period of growth and chromosome replication, 90% of the cell’s life

G1, S, and G2 phases

sister chromatids

form through replication, identical sections of the chromosome

centromere

holds the sister chromatids together

chromatin

uncoiled DNA, form of DNA during interphase

G1 phase

initiates interphase, active growth phase, can vary in length, cell increases in size and synthesizes proteins

the length of this phase determines the length of the entire cell cycle

S phase

period of DNA synthesis

G2

cell prepares to divide, grows and synthesizes proteins

M phase

mitosis/meiosis occurs, results in two or four daughter cells

mitosis

division and distribution of the cell’s DNA to two daughter cells, occurs in somatic cells

karyokinesis

nuclear division

prophase

prepares the cell for karyokinesis, chromatin condenses into chromosomes, nuclear membrane dissolves, centriole pairs separate and move towards opposite poles of the cell

metaphase

centrioles now at opposite poles, formation of spindle fibers that attach to each chromatid at the kinetochore, spindle fiber aligns the chromosomes along the metaphase plate

kinetochore

a protein located at the centromere of the chromosome

anaphase

separation of sister chromatids to each chromosome, centromeres split, pulled to opposite poles of the cell as spindle fibers shorten

telophase

spindle apparatus disappears, nuclear membrane forms around each set of newly formed chromosomes, cells are diploid, chromosomes uncoil into their interphase form

cytokinesis

cytoplasmic division, at the end of mitosis/meiosis

cleavage furrow

forms in animals during cytokinesis, cell membrane indents along the equator of the cell, eventually pinching and separating cell membranes

cell plate

forms in plants during cytokinesis between the two nuclei, spltis plant cell in half, allowing the cell to divide

meiosis

production of sex cells, producing haploid cells (half the number of chromosomes)

ploidy

how many chromosomes an organism has in a homologous set

homologous chromosomes

share structure and gene locations, but can have different alleles

crossing over

occurs in prophase I of meiosis, genetic exchange between chromatids of homologous chromosomes, increases genetic diversity

synapsis

the process of homologous chromosomes coming together for crossing over into a tetrad structure

chiasmata

the exact parts of the chromosomes where sister chromatids interact

disjunction

occurs in anaphase I, where each chromosome of paternal origin separaates from its homologue of maternal origin

nondisjunction

can occur in anaphase I or II, cells do not separate appropriately during meiosis, daughter cells will have an incorrect number of chromosomes

intermediate daughter cells

found in telophase I, where cells are now haploid, but their chromosomes have two sister chromatids

metabolism

the sum of all chemical reactions that occur in the body

catabolism

breaking down chemicals and releasing energy, eg. cellular respiration

anabolism

synthesizing chemicals, requires energy, eg. DNA replication and protein synthesis

cellular respiration

the biochemical conversion of chemical energy into usable energy (ATP) —> aerobic or anaerobic

carbohydrates and fat are favoured due to energy-rich C-H bonds, metabolism removes H and energy is released

OXIDIZED

carbohydrates are _______ to CO2 during cellular respiration, releases energy (similar to combustion)

aerobic respiration

occurs in the presence of O2, yields a total of 36-38 ATP, 3 stages: pyruvate decarboxylation, citric acid cycle, electron transport chain

anaerobic respiration

occurs in absence of O2, fermentation (alcohol or lactic acid), need to regenerate NAD+ for glycolysis to continue, does not produce ATP (only the 2 from glycolysis), pyruvate is reduced to lactic acid or ethanol

external respiration

the inhaling and exhaling of air into and out of the lungs and the exchange of has between the alveoli and blood

internal respiration

the exchange of gas between individual cells and the extracellular fluid

law of conservation of energy

if energy is released during a reaction, then the products must have LESS potential energy than the reactants

glycolysis

1 glucose —> 2 pyruvate (+ ATP + NADH), NAD+ reduced to NADH and glucose oxidized

3 stages: energy investment stage, cleavage stage, energy payout phase

energy investment stage

steps 1-3 of glycolysis, 2 ATP used by kinases to produce fructose 1,6-bisphosphate

cleavage stage

step 4 of glycolysis, splits fructose 1,6-bisphosphate into glyceraldehyde 3-phosphate (PGAL) and dihidroxyacetone phosphate (DHAP), DHAP isomerized to PGAL

energy payout phase

steps 5-9 of glycolysis, results in ATP via substrate level phosphorylation, occurs twice due to 2 PGAL molecules, NAD+ reduced to NADH by a dehydrogenase

net reaction for glycolysis

glucose + 2 ADP + 2 Pi + NAD+ —> 2 pyruvate + 2 ATP + 2 NADH + 2 H+ + 2 H2O

substrate level phosphorylation

produces ATP, ATP synthesis coupled with the oxidation of glucose (without an intermediate electron carrier such as NADH or FADH2)

alcohol fermentation

occurs in yeast and some bacteria, pyruvate is converted to ethanol and NAD+ regenerated

lactic acid fermentation

occurs in certain fungi and bacteria and in human muscle cells, pyruvate reduced to lactic acid and NAD+ is regenerated

pyruvate decarboxylation

aka bridge reaction, pyruvate transported through both mitochondrial membranes to the IMM, pyruvate loses a CO2 and is transferred to coenzyme A to form acetyl-CoA, NAD+ reduced to NADH

citric acid cycle

per 1 molecule of glucose/2 pyruvate —> 6 NADH, 2 FADH2, 4 CO2, 2 ATP produced, also regenerates oxaloacetate

net reaction of citric acid cycle

2 acetyl-CoA + 6 NAD+ + 2 FAD + 2 GDP + 2 Pi + 4 H2O —> 4 CO2 + 6 NADH + 2 FADH2 + 2 GTP + 4 H+ + 2 CoA

prokaryotic metabolism

citric acid cycle occurs in the cytosol and the ETC occurs in the bacterial membrane itself

electron transport chain

located on the inside of the inner mitochondrial membrane, ATP produced when high energy potential electrons are transferred from NADH and FADH2 to oxygen - oxidative phosphorylation, 4 complexes & multiple cytochromes

O2 is the final electron acceptor and forms water: 2 H+ + 2e- + 1/2 O2 —> H2O

cytochromes

most ETC molecules, active site resembles hemoglobin, electron carriers, contains a central iron atom for a reversible redox reaction

ATP generation

involves coupling the oxidation of NADH and FADH2 to the phosphorylation of ADP, a proton gradient is maintained by the ETC and pumps H+ out of the matrix

proton motive force

drives H+ back across the membrane and into the matrix, but H+ must travel through a channel (ATP synthase)

ATP synthase

H+ passes through and enough energy is released to phosphorylate ADP to ATP

oxidative phosphorylation

= ETC + phosphorylation of ADP by ATP synthase, requires electron carriers

NADH

cannot cross membrane in eukaryotes, cell needs to expend energy to cross which uses ATP (not required in prokaryotes)

body preferences of energy

carbohydrates > fats > proteins

carbohydrates

disaccharides hydrolyzed to monosaccharides, which can be converted to glucose or glycolytic intermediates, glycogen stored in liver can also be converted when needed