DAT Photosynthesis and Cell Div. Flashcards
Photosynthesis:
biological process done by
photoautotrophs (plants, some bacteria and protists);
captures energy from sunlight and converts it to chemical
energy stored in the form of glucose
* Takes place in the chloroplast
* Overall Reaction: 6CO2 + 6H2O → C6H12O6 + 6O2
Chloroplast:
organelle that is only found in
photoautotrophs; contains chlorophyll (light absorbing
pigment with a porphyrin ring that has an Mg atom in the
center; similar structure to hemoglobin)
Chloroplast Structure (external to internal):
- Outer membrane (smooth)
- Intermembrane space
- Inner membrane (smooth)
- Stroma (cytoplasm of chloroplast)
Stroma Structure
a. Stroma lamellae: connect thylakoids together
b. Thylakoids: membrane bound flattened disks
found in the stroma
i. Thylakoid membrane: contain chlorophyll
ii. Thylakoid lumen: space enclosed by
thylakoid membrane
iii. Granum: stack of thylakoids
Photosynthesis includes…
light dependent and independent rxns
Light-Dependent Reactions:
include cyclic and noncyclic
photophosphorylation using chlorophyll found in
photosystems
Photosystems (PS):
(PS): large chlorophyll containing
proteins found in the thylakoid membrane.
Action Spectrum
plots wavelengths of light that are
most effective at causing photosynthesis
Red/blue light:
highest rate of photosyn
Green light:
lowest rate of photosynthesis (chlorophyll
reflects green wavelength of light instead of absorbing
it; this is why plants are green)
Noncyclic Photophosphorylation
- Sunlight hits PS II → photons from light excite
electrons (boosts electrons to higher energy level) - High energy electrons passed to primary electron
acceptor - Primary electron acceptor passes electrons through
the electron transport chain (ETC), pumps protons
(H+) against concentration gradient from stroma ➞
thylakoid lumen (creates an electrochemical
gradient) - Protons flow through ATP synthase down their
concentration gradient, catalyzing the conversion of
ADP to ATP
a. This ATP is used to power photosynthesis.
Cellular respiration still occurs to produce
energy in plants. - Electrons (now low-energy) arrive at PS I ➞ photons
from sunlight re-excite electrons to higher energy
level - Electrons are passed to an electron acceptor and
travel down another ETC - NADPH is formed by combining high energy
electrons with NADP+
a. NADPH transports high energy electrons to the
Calvin cycle for glucose production
Photolysis:
splitting of water by light that occurs in PS II.
Cyclic Photophosphorylation
Steps: occurs in the stroma
lamellae; only involves PS I
1. Electrons in PS I get excited by sunlight to a high
energy state
2. Electrons get recycled passed back to the first ETC,
allowing more pumping of H+ and making more
ATP instead of NADPH (replenishes the ATP used in 3 phases of Calvin cycle
(1. Carbon fixation: taking carbon from an inorganic
source (CO2 in atmosphere) and converting it to an
organic compound (glucose)
a. Done by autotrophs (plants, photosynthetic
organisms, chemoautotrophic prokaryotes)
2. Reduction (steps that use up ATP and NADPH from
light reactions)
3. Regeneration: intermediates are regenerated so
cycle can continue)
Important Steps of Calvin Cycle:
- RuBisCo (most abundant enzyme on Earth)
combines CO2 with RuBP, forming a 6 carbon
intermediate (carbon fixation phase) - 6 carbon molecule is broken into two 3-carbon
phosphoglycerate (PGA) molecules - PGA is phosphorylated to G3P (using ATP and
NADPH during the reduction phase) - Most G3P is converted back to RuBP (requires ATP)
and remaining G3P is used to make glucose
(regeneration phase)
a. 1 molecule of glucose is produced with 6 turns
of the cycle (1 cycle produces 2 G3P molecules,
so 6 cycles produce 12 G3P. 10 are used to
reform RuBP, and the remaining 2 are used to
make glucose)
Photorespiration:
an undesirable process which reduces
the efficiency of carbon fixation, forming useless
byproducts. Occurs when RuBisCo binds O2 instead of CO2
C2 (type of photosynthesis)
photorespiration; product = useless 2 carbon molecule
* Takes place in all plants
* Some plants have no way to stop C2 and
photosynthesize less efficiently
C3: normal photosynthesis
- Takes place in all plants in the mesophyll cells
C4:
prevents photorespiration by physically separating light
and dark reactions
CAM:
minimizes water loss via temporal separation instead
of spatial (common in plants in dry environments e.g.
cactus)
Stomata
pores found on bottom of leaves for gas
exchange. In most plants, stomata are always open for
continuous exchange of CO2 and O2, allowing water to
escape easily in certain environments
what do CAM plants do differently
only open their stomata at night so that
CO2 can enter and less water is lost. However, there
is no sunlight at night, so there is no ATP/NADPH
from the light reactions to power the Calvin Cycle
Cell division
how cells replicate to increase their number.
Chromatin
a condensed form of DNA that is wrapped
around histones. DNA is stored as chromatin, but during
cell division, it condenses even more into chromosomes.
Chromosomes:
dense packaging of chromatin, existing
during mitosis and meiosis. Chromosomes can be in
duplicated or unduplicated forms.
Chromatid:
one half of a duplicated chromosome
Sister Chromatids:
two duplicated chromatids that
are completely identical to one another. They can
connect at the centromere to form an X-shaped
chromosome
Centromere:
region where two sister chromatids are
connected; kinetochores attach here
n =
number of chromosomes in a set
Haploid Human cells:
cells: n=23,
Diploid Cells (2n)
have 2 sets of chromosomes: one
from the mother and one from the father. The vast
majority of human cells are diploid.
Homologous Chromosomes
set of a chromosomes
(one from each parent) in a pair. Found in diploid cells.
Homologous chromosomes are similar in length, gene
position, and centromere position. They carry genetic
information for the same traits, but are not genetically
identical.
Centrosomes
the Microtubule Organizing Centers
(MTOCs) of animal cells. A centrosome is composed of 2
centrioles perpendicular to each other.
Spindle Fibers:
microtubules that emerge from the
centrosome. They allow chromosomes and chromatids
to be separated during specific phases of cell division.
Mitosis:
nuclear division that creates a pair of diploid cells
that are genetically identical to the original cell
Mitosis Overview:
prophase → prometaphase →
metaphase → anaphase → telophase and cytokinesis
Prophase
- Chromatin condenses into chromosomes
- Nucleolus disappears
- Mitotic spindle begins to form
- Centrosomes begin to move towards opposite ends of
the cell
Prometaphase
- Nucleus disassembles
- Chromosomes condense even further
- Each chromatid is attached to a kinetochore
- Mitotic spindle further develops
- Spindle fibers begin to attach to kinetochores of
chromosomes
Metaphase
- Chromosomes are lined up across the center of the cell
(aka metaphase plate) - Centrosomes have reached opposite ends of the cell
- Mitotic spindle is fully developed
- All chromosomes are attached to spindle fibers via
kinetochores
Karyotyping
(physical observation of a cell’s
chromosomes with a microscope)
Anaphase
- Microtubules shorten
- Sister chromatids are pulled apart
- Once separated, each sister chromatid is now
considered to be an individual chromosome
Telophase
- Nucleoli redevelop
- Two nuclear envelopes develop
- Chromosomes decondense back into chromatin
- Spindle fibers disappear
- Cytokinesis occurs during telophase
- Mitosis: the nucleus duplicates
- Cytokinesis: the rest of the cell duplicates
Cytokinesis:
physical division of the cytoplasm to form two
cells.
Animal cells form a
cleavage furrow (contractile ring
formed by actin and myosin) forms; ring contracts to
separating the dividing cells into two
Plant cells form a
cell plate that develops between the
two nuclei; essentially a cell wall that fuses with the
existing plant cell wall, separating the two cells
Meiosis:
nuclear division in that produces four haploid
gametes that are not genetically identical to the original
cell. Gametes are an organism’s reproductive cells (sperm in
males, eggs in females).
Cell Cycle:
an ordered sequence of events that occur
before and during cell division.
Interphase:
Interphase: when the cell is growing and preparing for
cell division, but not actively dividing. Interphase
ensures that each daughter cell will have enough
biological material. Cells spend most of the cell cycle in
interphase.
The phases of interphase include:
G1, S, G2, G0, m phase
G1 (Gap Phase 1):
cell grows in size and protein
synthesis begins (preparation for cell division).
‣ Usually the longest phase of the cell cycle
S (Synthesis Phase):
DNA and centrosomes are
replicated. Sister chromatids are formed.
G2 (Gap Phase 2):
final preparation for mitosis. Cell
continues to grow, and organelles replicate. Cell
checks that everything is ready (e.g. chromosomes
are replicated) to proceed with mitosis.
G0: resting phase.
Cells are active/functional, but
are not dividing or preparing to divide
Cells have to divide because of functional limitations:
SA to volume ratio, Genome to volume ratio
checkpoints of cell cycle
End of G1:, end of G2, M Checkpoint/Spindle Checkpoint
Density dependent inhibition:
cells stop dividing
when the surrounding cell density reaches a
maximum. Prevents overcrowded cells from
dividing.
Anchorage dependence:
cells will only divide when
attached to an external surface
a. Prevents cells from multiplying while floating
freely through the body
p53 gene:
an important tumor suppressor gene that
regulates cell division
* Mutation of p53 causes the cell to divide in an
uncontrolled manner and leads to tumor formation
