BIOL 1020 Exam 3

Photosynthesis

  • Process that converts solar energy into chemical energy

  • Directly or indirectly, photosynthesis nourishes the entire world

Classification by Energy and Carbon Sources

  • Energy Source

    • Chemotrophs: can only get energy directly from chemical compounds

    • Phototrophs: get energy directly from light (these organisms can use chemical compounds as energy sources as well)

  • 4 sub groups

    • Photoautotrophs: carry out photosynthesis

    • Photoheterotrophs: use light energy but cannot fix CO2; some non sulfur purple bacteria

    • Chemoautotrophs: obtain energy from reduced inorganic molecules and use some of it to fix CO2; some bacteria

      • These were the first cells on earth

    • Chemoheterotrophs: use organic molecules as both carbon and energy sources

Autotrophs and Heterotrophs

  • Autotrophs: obtain energy directly from the environment, and making organic molecules from inorganic molecules

  • Heterotrophs: get energy and carbon by breaking down organic molecules assembled by other organisms

Electromagnetic Spectrum

  • Molecules can absorb photons, thus becoming energized

Chloroplasts

  • In photosynthetic eukaryotes, photosynthesis occurs in chloroplasts

  • Chloroplasts have both an inner and outer membrane

  • Stroma: fluid-filled region inside the inner membrane

    • Sugars are built in the stroma (second stage of photosynthesis)

  • Thylakoids: disklike membranous sacs found in stroma (interconnected with each other and inner membrane)

  • Thylakoid Membrane: folded inner membrane that makes up thylakoids

  • Thylakoid Lumen: fluid-filled region inside a thylakoid

  • Granum: stack of thylakoids

  • Chlorophyll: main light harvesting molecule, found in the thylakoid membrane

  • Pigments

    • Pigment: an organic molecules that selectively absorbs light of specific wavelengths

    • Reflects wavelengths no absorbed and gives it color

    • Chlorophyll a

      • Most common photosynthetic pigment

      • Absorbs violet-blue and red light

      • Reflects green

    • Accessory pigments are also found in the thylakoid membrane

      • Can transfer captured energy to chlorophyll a

Photosynthesis

  • H20 is oxidized and CO2 is reduced (endergonic process)

  • Divided Into:

    • Light Reactions

      • Capture light energy

      • Consume water

      • Produce oxygen

      • Energy is placed in ATP and NADPH in the stroma

    • C3 Cycle

      • Consumes CO2 and energy (proved by ATP and NADPH)

      • Produces carbohydrates

    • In many ways, this is the reverse of aerobic respiration

  • In the thylakoids light energy is received and water is split providing a source of electrons and protons H+, producing O2 gas as waste and NADP and ATP

  • C3 Cycle

    • Carbon fixation (carbon uptake)

      • Taking carbon atoms from inorganic sources (atmosphere) and using them to produce organic molecules

      • Builds glucose from CO2

      • CO2 combines with the 5-carbon compound ribulose 1,5-biphosphate (RuBP)

 

  • Carbon reduction

    • 3-PGA is reduced to glyceraldehyde 3-phosphate (G3P) in two steps; in the process, ATP and NADPH are used

    • From 6 CO2 you get 12 G3P

    • 2 G3P are removed and used to make glucose or fructose (thus 6 carbons leave to make C6H12O6)

    • Remaining 10 G3P are used to regenerate RuBP

  • RuBP regeneration

    • Series of 10 reactions

    • Rearrange the 10 G3P to form 6 ribulose phosphate molecules

  • C3 Plants: Photorespiration

    • Stomata is closed so CO2 cannot enter and O2 cannot leave

      • Low CO2, high O2

    • Photorespiration

      • At high O2 levels, rubisco attaches oxygen to RuBP instead of carbon

      • One PGA and one glycolate form

      • Glycolate broken down into CO2 and H2O

  • C4 Plants

    • Named because they preface the carbon cycle with an alternate mode of carbon fixation that forms a four-carbon compound as its first product

  • CAM Plants (Crassulacean Acid Metabolism)

    • A second photosynthetic adaption to arid conditions has evolved in pineapples, cacti, other plants

    • Only opens stomata at night to keep from losing water, fixes carbon at night

    • Forms 4-carbon molecule at night

  • C4 works by altering the location of initial CO2 fixation

  • CAM works by altering the time of initial CO2 fixation

Why do cells divide?

  • Multicellular eukaryotes depend on cell division for…

    • Development from a fertilized cell

    • Growth

    • Repair

  • Cell division is an integral part of cell life

Cells

  • Somatic cells (body cells/nonreproductive cells) 2n

  • Gametes (sex cells/reproductive cells: sperm and egg) n

  • Prokaryotes reproduce by a type of cell division called binary fission

    • Usually a singular, circular chromosome

Eukaryotic DNA

  • Chromatin: long DNA molecule with associated proteins

  • Chromosomes: densely packaged chromatin

  • DNSA gives instructions to make protein or RNA molecule

  • Genome: organism's complete DNA sequence

Mitosis

  • Human cell might undergo one division in 24 hours

  • 4 Stages

    • Prophase

    • Metaphase

    • Anaphase

    • Telophase

  • Prophase

    • Chromatin condenses to form chromosomes

    • Each chromosome (duplicated during s phase) forms a pair of sister chromatids

      • Joined by a centromere

    • System of microtubules called the mitotic spindle, organizes between the two poles of the cell

    • By end of prophase, nuclear membrane has broken down and nucleoli have disintegrated

  • Metaphase

    • Chromosomes line up along the midplane of the cell (the metaphase plate)

      • Chromosomes are highly condensed

      • Mitosis checkpoint appears to be here

    • Sister chromatids separate and are moved toward opposite poles

  • Anaphase

    • Sister chromatids separate and are moved toward opposite poles

    • Motor proteins move the chromosomes towards the poles along the kinetochores microtubules

    • Overall, this process assures that each daughter cell will receive one of the duplicate sets of genetic material carried by the chromosomes

  • Telophase

    • Prophase is essentially reversed

      • Mitotic spindle is disintegrated

      • Chromosomes decondense

      • Nuclear membranes reform

  • Cytokinesis

    • Divides the cell into two daughter cells

    • Usually beings in telophase and ends

    • In animals, a cleavage furrow develops

    • In plants, a cell plate develops

    • Cytoplasm is usually distributed randomly but roughly equally between daughter cells

Cell Signaling

  • Endogenous: cells can receive signals to divide from within the cell

  • Exogeneous: cells can also be signaled to divide by chemical factors outside the cell

 

 Asexual Reproduction

  • Creates offspring that are genetically identical to each other and to the parent cell (clones)

  • Only mitotic cell division is required

  • Typically rapid and efficient compared to sexual reproduction

Sexual Reproduction

  • Occurs when specialized sex cells called gametes fuse to form a single cell called a zygote

  • Offspring are not genetically identical to their parents

  • Genetic recombination

    • May produce some offspring that are better adapted to the environment than either parent

    • May produce some offspring that are moor poorly adapted than either parent

  • Must have a way to half the number of chromosomes at some point, otherwise the number of chromosomes would double with each generation

    • Accomplishes through meiosis

    • Diploid cells give rise to haploid cells during meiosis

  • Most somatic cells are diploid

  • Diploid (2n): two complete sets

  • Haploid (n): one set

  • Polyploid (3n or more): extra sets

  • Three events are unique to meiosis and all occur in meiosis I

    • Synapsis and crossing over in prophase I

    • At metaphase I --> paired homologous chromosomes (tetrads)

    • At anaphase I, homologous chromosomes, NOT sister chromatids separate

  • Genetic variation in sexual life cycles contributes to evolution

    • Mutations are the original source of genetic diversity

    • Mutations create different versions of genes called alleles

    • Reshuffling alleles during sexual reproduction produces genetic variation

  • Crossing Over

    • Produces recombinant chromosomes, which combine DNA inherited from each parent

    • Crossing over begins very early in prophase I, as homologous chromosomes pair up gene by gene

    • In crossing over, homologous portions of two non-sister chromatids trade places

    • Crossing over contributes to genetic variation by combining DNA from two parents into a single chromosome

  • Independent Assortment

    • Homologous pairs of chromosomes orient randomly at metaphase I of meiosis

  • Random Fertilization

    • Any sperm can fuse with any ovum