Biology

Question 1

Prokaryote

Answer 1

a group of organisms whose cells lack a membrane-bound nucleus (karyon). The word prokaryote comes from the Greek πρό- (pro-) “before” and καρυόν (karyon) “nut or kernel”.[2][3] Prokaryotes do not have a membrane bound nucleus, mitochondria, or any other membrane-bound organelles. They include two major classification domains of life: the Bacteria and the Archaea.

Question 2

Bacteria

Answer 2

constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats.

Question 3

Archaea

Answer 3

Archaea were initially classified as bacteria, receiving the name archaebacteria. Despite this visual similarity to bacteria, archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes, notably the enzymes involved in transcription and translation. Other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes. Archaea use more energy sources than eukaryotes: these range from organic compounds such as sugars, to ammonia, metal ions or even hydrogen gas. Salt-tolerant archaea (the Haloarchaea) use sunlight as an energy source, and other species of archaea fix carbon; however, unlike plants and cyanobacteria, no species of archaea does both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria and eukaryotes, no species form spores.

Question 4

binary fission

Answer 4

asexual reproduction by a separation of the body into two new bodies. In the process of binary fission, an organism duplicates its genetic material, or deoxyribonucleic acid (DNA), and then divides into two parts (cytokinesis), with each new organism receiving one copy of DNA.

Question 5

transposon

Answer 5

class of genetic elements that can “jump” to different locations within a genome.

Question 6

Bacterial conjugation

Answer 6

the transfer of genetic material (plasmid) between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells.

Question 7

Virus

Answer 7

a small infectious agent that replicates only inside the living cells of other organisms.

Question 8

Retrovirus

Answer 8

Retroviridae is a family of enveloped viruses that replicate in a host cell through the process of reverse transcription. A retrovirus is a single-stranded RNA virus that stores its nucleic acid in the form of an mRNA genome (including the 5’ cap and 3’ PolyA tail) and targets a host cell as an obligate parasite. Once inside the host cell cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the usual pattern, thus retro (backwards). This new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus.

Question 9

Provirus

Answer 9

A provirus is a virus genome that is integrated into the DNA of a host cell. In the case of bacterial viruses (bacteriophages), proviruses are often referred to as prophages.

Question 10

Endogenous retrovirus

Answer 10

are endogenous viral elements in the genome that closely resemble and can be derived from retroviruses. They are abundant in the genomes of jawed vertebrates and they occupy as much as 4.9% of the human genome.

Question 11

horizontal transduction

Answer 11

Horizontal gene transfer (HGT) refers to the transfer of genes between organisms in a manner other than traditional reproduction. Also termed lateral gene transfer (LGT), it contrasts with vertical transfer, the transmission of genes from the parental generation to offspring via sexual or asexual reproduction. Horizontal gene transfer is the primary reason for bacterial antibiotic resistance.

Question 12

Bacteriophage

Answer 12

a virus that infects and replicates within a bacterium. The term is derived from ‘bacteria’ and the Greek φαγεῖν phagein “to devour”.

Question 13

Lytic cycle

Answer 13

The lytic cycle is one of the two cycles of viral reproduction, the other being the lysogenic cycle. The lytic cycle results in the destruction of the infected cell and its membrane. A key difference between the lytic and lysogenic phage cycles is that in the lytic phage, the viral DNA exists as a separate molecule within the bacterial cell, and replicates separately from the host bacterial DNA. The location of viral DNA in the lysogenic phage cycle is within the host DNA, therefore in both cases the virus/phage replicates using the host DNA machinery, but in the lytic phage cycle, the phage is a free floating separate molecule to the host DNA.

Question 14

Lysogenic cycle

Answer 14

Lysogeny, or the lysogenic cycle, is one of two methods of viral reproduction (the lytic cycle is the other). Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium’s genome or formation of a circular replicon in the bacterium’s cytoplasm. In this condition the bacterium continues to live and reproduce normally. The genetic material of the bacteriophage, called a prophage, can be transmitted to daughter cells at each subsequent cell division, and a later event (such as UV radiation or the presence of certain chemicals) can release it, causing proliferation of new phages via the lytic cycle.

Question 15

Somatic cell

Answer 15

any biological cell forming the body of an organism; that is, in a multicellular organism, any cell other than a gamete, germ cell, gametocyte or undifferentiated stem cell

Question 16

Germ cell

Answer 16

any biological cell that gives rise to the gametes of an organism that reproduces sexually.

Question 17

DNA

Answer 17

Deoxyribonucleic acid (DNA) is a molecule that encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses. DNA is a nucleic acid; alongside proteins and carbohydrates, nucleic acids compose the three major macromolecules essential for all known forms of life.

Question 18

Nucleotides

Answer 18

organic molecules that serve as the monomers, or subunits, of nucleic acids like DNA and RNA. The building blocks of nucleic acids, nucleotides are composed of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and at least one phosphate group.

Question 19

Monomer

Answer 19

a molecule that may bind chemically to other molecules to form a polymer.

Question 20

Polymer

Answer 20

a large molecule, or macromolecule, composed of many repeated subunits.

Question 21

chromosome

Answer 21

any of several threadlike bodies, consisting of chromatin, that carry the genes in a linear order: the human species has 23 pairs, designated 1 to 22 in order of decreasing size and X and Y for the female and male sex chromosomes respectively.

Question 22

Homologous chromosome

Answer 22

a set of one maternal chromosome and one paternal chromosome that pair up with each other inside a cell during meiosis. These copies have the same genes in the same locations, or loci.

Question 23

Chromatid

Answer 23

one copy of a duplicated chromosome, which is generally joined to the other copy by a single centromere.

Question 24

Chromatin

Answer 24

the combination or complex of DNA and proteins that make up the contents of the nucleus of a cell (only found in eukaryotic cells). The primary protein components of chromatin are histones that compact the DNA.

Question 25

codon

Answer 25

A codon is a sequence of three DNA or RNA nucleotides that corresponds with a specific amino acid or stop signal during protein synthesis.

Question 26

DNA replication

Answer 26

the process of producing two identical replicas from one original DNA molecule

Question 27

Transcription

Answer 27

the first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase (DNA -> mRNA)

Question 28

Translation

Answer 28

the process in which cellular ribosomes create proteins. It is part of the process of gene expression. In translation, messenger RNA (mRNA) produced by transcription is decoded by a ribosome complex to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein.

Question 29

Cytokinesis

Answer 29

(from the Greek cyto- “cell” (cf. cytology) and kinesis “motion, movement”) is the process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells.

Question 30

Apoptosis

Answer 30

(from Ancient Greek apo, “away from” and ptōsis, “falling”) is the process of programmed cell death (PCD). Biochemical events lead to characteristic cell changes (morphology) and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation.

Question 31

Cellular respiration

Answer 31

the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.

Question 32

Glycolysis

Answer 32

(from glycose, an older term for glucose + -lysis degradation) is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+. The free energy released in this process is used to form the high-energy compounds ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide). Occurs in most organisms in the cytosol of the cell. The entire glycolysis pathway can be separated into two phases: 1. The Preparatory Phase – in which ATP is consumed and is hence also known as the investment phase, and 2. The Pay Off Phase – in which ATP is produced (4 -2= Net 2 ATP).

Question 33

Citric acid cycle

Answer 33

(also known as the tricarboxylic acid cycle (TCA cycle), or the Krebs cycle) a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats and proteins into carbon dioxide and chemical energy in the form of adenosine triphosphate (ATP). In addition, the cycle provides precursors of certain amino acids as well as the reducing agent NADH. In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion. In prokaryotic cells, such as bacteria which lack mitochondria, the TCA reaction sequence is performed in the cytosol with the proton gradient for ATP production being across the cell’s surface (plasma membrane) rather than the inner membrane of the mitochondrion.

Question 34

Electron transport chain

Answer 34

a series of compounds that transfer electrons from electron donors to electron acceptors via redox reactions, and couples this electron transfer with the transfer of protons (H+ ions) across a membrane. This creates an electrochemical proton gradient that drives ATP synthesis, or the generation of chemical energy in the form of adenosine triphosphate (ATP)

Question 35

Fermentation

Answer 35

a metabolic process that converts sugar to acids, gases and/or alcohol in the absence of oxygen (when the electron transport chain is unusable) and becomes the cell’s primary means of ATP (energy) production. It occurs in yeast and bacteria, but also in oxygen-starved muscle cells, as in the case of lactic acid fermentation.

Question 36

Oxidation-Reduction

Answer 36

“OIL-RIG” oxidation is loss, reduction is gain (of electron or Hydrogen atom)

Question 37

Phosphorylation

Answer 37

the addition of a phosphate (PO43−) group. ATP, the “high-energy” exchange medium in the cell, is synthesized in the mitochondrion by addition of a third phosphate group to ADP in a process referred to as oxidative phosphorylation. ATP is also synthesized by substrate-level phosphorylation during glycolysis. ATP is synthesized at the expense of solar energy by photophosphorylation in the chloroplasts of plant cells. Phosphorylation of sugars is often the first stage of their catabolism. It allows cells to accumulate sugars because the phosphate group prevents the molecules from diffusing back across their transporter.

Question 38

Photophosphorylation

Answer 38

the phosphorylation of ADP to form ATP using the energy of sunlight in photosynthesis

Question 39

Substrate phosphorylation

Answer 39

a type of metabolic reaction that results in the formation of adenosine triphosphate (ATP) or guanosine triphosphate (GTP) by the direct transfer and donation of a phosphoryl (PO3) group to adenosine diphosphate (ADP) or guanosine diphosphate (GDP) from a phosphorylated reactive intermediate. Note that the phosphate group does not have to come directly from the substrate. By convention, the phosphoryl group that is transferred is referred to as a phosphate group.

Question 40

Oxidative phosphorylation

Answer 40

the metabolic pathway in which the mitochondria in cells use their structure, enzymes, and energy released by the oxidation of nutrients to reform ATP. Almost all aerobic organisms carry out oxidative phosphorylation. This pathway is probably so pervasive because it is a highly efficient way of releasing energy, compared to alternative fermentation processes such as anaerobic glycolysis.

Question 41

Chemiosmosis

Answer 41

the movement of ions across a selectively permeable membrane, down their electrochemical gradient. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane during cellular respiration.

Question 42

Chloroplast

Answer 42

organelles, specialized subunits, in plant and algal cells. Their main role is to conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, and stores it in the energy storage molecules ATP and NADPH while freeing oxygen from water. They then use the ATP and NADPH to make organic molecules from carbon dioxide in a process known as the Calvin cycle. Chloroplasts carry out a number of other functions, including fatty acid synthesis, much amino acid synthesis, and the immune response in plants. They have their own DNA (much like mitochondria)

Question 43

Stroma

Answer 43

the fluid in between grana, where carbohydrate-formation reactions occur in the chloroplasts of plant cells photosynthesizing

Question 44

Thylakoid

Answer 44

a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. They consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana (singular: granum). Grana are connected by intergranal or stroma thylakoids, which join granum stacks together as a single functional compartment.

Question 45

Lumen

Answer 45

In biology, a lumen (Lat. lūmen, an opening or light) (pl. lumina) is the inside space of a tubular structure, such as an artery or intestine.[1] By extension, the term lumen is also used to describe the inside space of a cellular component or structure, such as the endoplasmic reticulum and thylakoid of plants.

Question 46

Photosystem II (P680)

Answer 46

is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem, enzymes capture photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol. The energized electrons are replaced by oxidizing water (oxidizing oxygen!) to form hydrogen ions and molecular oxygen.
By replenishing lost electrons with electrons from the splitting of water, photosystem II provides the electrons for all of photosynthesis to occur. The hydrogen ions (protons) generated by the oxidation of water help to create a proton gradient that is used by ATP synthase to generate ATP. The energized electrons transferred to plastoquinone are ultimately used to reduce NADP+
to NADPH or are used in cyclic photophosphorylation.

Question 47

Photosystem I (P700)

Answer 47

the second (discovered first) photosystem in the photosynthetic light reactions of algae, plants, and some bacteria. It is an integral membrane protein complex that uses light energy to mediate electron transfer from plastocyanin to ferredoxin. The PS I system comprises more than 110 co-factors, significantly more than photosystem II. These various components have a wide range of functions.
Photons of light photoexcite pigment molecules (Chlorophylls and carotenoids) in the antenna complex. Energy from each photon is transferred to an electron, causing an excited state. The antenna complex is composed of molecules of chlorophyll and carotenoids mounted on two proteins. These pigment molecules transmit the resonance energy from photons when they become photoexcited. Antenna molecules can absorb all wavelengths of light within the visible spectrum. 
The P700 reaction center is composed of modified chlorophyll a that best absorbs light at a wavelength of 700nm, with higher wavelengths causing bleaching.[13] P700 receives energy from antenna molecules and uses the energy from each photon to raise an electron to a higher energy level. These electrons are moved in pairs in an oxidation/reduction process from P700 to electron acceptors.

Question 48

Förster resonance energy transfer/ Fluorescence resonance energy transfer (FRET)

Answer 48

is a mechanism describing energy transfer between two light-sensitive molecules (chromophores).[1] A donor chromophore, initially in its electronic excited state, may transfer energy to an acceptor chromophore through nonradiative dipole–dipole coupling.[2] The efficiency of this energy transfer is inversely proportional to the sixth power of the distance between donor and acceptor, making FRET extremely sensitive to small changes in distance.[3]

Question 49

Chlorophyll

Answer 49

a green pigment found in cyanobacteria and the chloroplasts of algae and plants.[2] Its name is derived from the Greek words χλωρός, chloros (“green”) and φύλλον, phyllon (“leaf”).[3] Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to absorb energy from light. Chlorophyll absorbs light most strongly in the blue portion of the electromagnetic spectrum, followed by the red portion. Conversely, it is a poor absorber of green and near-green portions of the spectrum, hence the green color of chlorophyll-containing tissues.

Question 50

Chlorophyll a

Answer 50

a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light.[3] It also reflects green/yellow light, and as such contributes to the observed green color of most plants. This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and prochlorophytes because of its role as primary electron donor in the electron transport chain.[4] Chlorophyll a also transfers resonance energy in the antenna complex, ending in the reaction center where specific chlorophylls P680 and P700 are located.

Question 51

Light-independent reactions/Calvin Cycle

Answer 51

chemical reactions that convert carbon dioxide and other compounds into glucose. These reactions occur in the stroma, the fluid-filled area of a chloroplast outside of the thylakoid membranes. These reactions take the light-dependent reactions and perform further chemical processes on them. There are three phases to the light-independent reactions, collectively called the Calvin cycle: carbon fixation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.
Despite its name, this process occurs only when light is available. Plants do not carry out the Calvin cycle by night. They, instead, release sucrose into the phloem from their starch reserves. This process happens when light is available independent of the kind of photosynthesis (C3 carbon fixation, C4 carbon fixation, and Crassulacean Acid Metabolism); CAM plants store malic acid in their vacuoles every night and release it by day in order to make this process work.

Question 52

Carbon fixation

Answer 52

the conversion process of inorganic carbon (carbon dioxide) to organic compounds by living organisms. The most prominent example is photosynthesis, although chemosynthesis is another form of carbon fixation that can take place in the absence of sunlight. Organisms that grow by fixing carbon are called autotrophs. Autotrophs include photoautotrophs, which synthesize organic compounds using the energy of sunlight, and lithoautotrophs, which synthesize organic compounds using the energy of inorganic oxidation. Heterotrophs are organisms that grow using the carbon fixed by autotrophs. The organic compounds are used by heterotrophs to produce energy and to build body structures. “Fixed carbon”, “reduced carbon”, and “organic carbon” are equivalent terms for various organic compounds.

Question 53

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO)

Answer 53

an enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants to energy-rich molecules such as glucose. In chemical terms, it catalyzes the carboxylation of ribulose-1,5-bisphosphate (also known as RuBP). It is probably the most abundant protein on Earth.

Question 54

Photorespiration

Answer 54

(also known as the oxidative photosynthetic carbon cycle, or C2 photosynthesis) is a process in plant metabolism which attempts to ameliorate the consequences of a wasteful oxygenation reaction by the enzyme RuBisCO. The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin-Benson cycle, however approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), producing a product that cannot be used within the Calvin-Benson cycle. This process reduces efficiency of photosynthesis,

Question 55

C3 carbon fixation

Answer 55

converts carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) into 3-phosphoglycerate through the following reaction:

CO2 + RuBP → (2) 3-phosphoglycerate

This reaction occurs in all plants as the first step of the Calvin-Benson cycle.

Question 56

C4 carbon fixation

Answer 56

a biochemical mechanisms used in carbon fixation, and is believed to have evolved more recently to overcome the tendency of the enzyme RuBisCO to wastefully fix oxygen rather than carbon dioxide in what is called photorespiration. This is achieved by using a more efficient enzyme to fix CO2 in mesophyll cells and shuttling this fixed carbon via malate or aspartate to bundle-sheath cells. In these bundle-sheath cells, RuBisCO is isolated from atmospheric oxygen and saturated with the CO2 released by decarboxylation of the malate or oxaloacetate. These additional steps, however, require more energy in the form of ATP. Because of this extra energy requirement, C4 plants are able to more efficiently fix carbon in only certain conditions, with the more common C3 pathway being more efficient in other conditions.
It is named for the 4-carbon molecule present in the first product of carbon fixation in the small subset of plants known as C4 plants (in contrast to the 3-carbon molecule)

Question 57

Crassulacean acid metabolism

Answer 57

also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions.[1] In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide The CO2 is stored as the four-carbon acid malate, and then used during photosynthesis during the day. The pre-collected CO2 is concentrated around the enzyme RuBisCO, increasing photosynthetic efficiency.