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6.3/Energy in the Cell
Enzymes, cellular respiration, photosynthesis
27
Biology
10th Grade
05/30/2011

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Term
Enzymes
Definition
• Proteins that allow chemical reactions to take place
• Acts on a substrate that fits specifically into the enzyme’s active site
• Can break substrates into two products or merge two substrates into one
• Doesn’t get changed in the process—just a catalyst, speeds up reactions
• Lower activation energy of a reaction
Term
Substrate
Definition
• Acted on by enzymes by going into the active site
Term
Catalysis
Definition
• The process of speeding up reactions to a greater rate than they would happen normally
• Enzymes do this
Term
Reaction Coupling
Definition
• Couple energetically unfavorable reactions with energetically favorable ones
• Like a waterfall powering a turbine of a generator  do work
• Powers active transport, can make complex molecules
Term
Energy Carrier
Definition
• Molecules that can store a little energy
• ATP is the most important one for a cell
o Has energy in covalent bonds attached to phosphate groups
o When one of these bonds is broken  ADP and releases energy
• Some carry energy in extra electrons like NAD+  NADH; NADP+  NADPH; FAD  FADH2
• Energy is being carried in the second form and is released when the hydrogens are taken away
Term
Respiration
Definition
• Process where cells break down food and make it into usable energy
• Starts with glucose, produces ATP and CO2
• Glycolysis  citric acid cycle (Krebs cycle)  ETC  oxidative phosphorylation
• C6H12O6 + 6 O2  6 H2O + 6CO2 + energy
Term
Glycolysis
Definition
• First step of respiration
• glucose + 2 NAD+ + 2 ADP  2 NADH + 2 ATP + 2 pyruvate
• Three steps
o Cell puts in two ATP and glucose is rearranged into six-carbon sugar
o Cleavage: cell breaks six-carbon sugar into two three-carbon intermediate sugars
o Those molecules made into two pyruvate—two NAD+  NADH and 4 ATP made
• Only part of respiration that prokaryotic cells can do because it doesn’t require mitochondria
• Diagram page 84
Term
Pyruvate
Definition
• Product of glycolysis
• Has three carbons
• Converted to acetyl CoA before Krebs cycle
Term
Pyruvate to Acetyl CoA
Definition
• Has to happen for the Krebs cycle to work
• Three enzymes from mitochondria used, called pyruvate dehydrogenase complex
• Acetyl CoA is a two-carbon sugar attached to a coenzyme
• Pyruvate + NAD+ + coenzyme A  NADH + CO2 + acetyl CoA (twice per glucose)
• Acetyl CoA can also come from fat molecules
Term
Citric Acid Cycle (Krebs Cycle)
Definition
• Release energy from pyruvate molecules and release CO2
• The acetyl CoA attached to oxaloacetate  citrate  name of cycle
• Energy taken over 10 steps  original oxaloacetate  can start over with another acetyl CoA
• Acetyl CoA + 2 H2O + 2 NAD+ + FAD + GDP  2 CO2 + 2 NADH + FADH2 + GTP + coenzyme A
• Energy gains: 3 NAD+  3 NADH, 1 FAD  1 FADH2, 1 GDP  1 GTP
• End of this, all carbons from original glucose released as CO2
• Diagram page 86
Term
Coenzyme
Definition
• A nonprotein thing needed to make an enzyme function
Term
Oxidative Phosphorylation
Definition
• Energy stored in electron carriers NADH and FADH2 is converted to usable energy in ATP
• Concentration gradient of H+ created by ETC
• H+ travel through ATP synthase to fix gradient  energy makes ADP into ~30 ATP
• Relies on oxygen—that’s why we need oxygen
• Diagram page 87
Term
Electron Transport Chain
Definition
• Series of proteins embedded in inner membrane of mitochondria
• Transports electrons from NADH/FADH2 down chain, they end up on an oxygen  water
• Hydrogen protons H+ are transported to other side of membrane
Term
Fermentation
Definition
• Process where NAD+ is regenerated from NADH in anaerobic conditions—without oxygen
• Alcoholic and lactic acid fermentation are two most common
Term
Alcoholic Fermentation
Definition
• Pyruvate from glycolysis  2-carbon ethanol, makes two additional ATP and releases 1 CO2
• Regenerates two NAD+ from NADH so they can be used for glycolysis
• Yeast and bacteria do this
• Anaerobic
Term
Lactic Acid Fermentation
Definition
• Pyruvate from glycolysis  lactate, makes two additional ATP
• Regernates two NAD+ from NADH so they can be used for glycolysis
• Animals do this, lactate buildiup  cramp
• Anaerobic
Term
Photosynthesis
Definition
• Plants capture energy from sunlight, then use it to make a big sugar molecule to store energy
• Capture carbon dioxide and release oxygen
• 6 H2O + 6 CO2 + light energy  C6H12O6 + H2O
• Light reactions and dark reactions
Term
Autotrophs
Definition
• Organisms that can produce their own food (like plants with photosynthesis)
Term
Heterotrophs
Definition
• Organisms that have to have some sort of outside food source of organic molecules
Term
Light Reactions
Definition
• Parts of photosynthesis that rely on sunlight and use chlorophyll
• Light energy from sun  usable chemical energy
• Happen in thylakoid membranes of chloroplast
• Use energy of excited electrons through photosystems
Term
Chlorophyll
Definition
• Key molecule of light reactions
• Pigment in the chloroplast that gives leaves green color
• When hit by light, an electron gets excited and has more energy
• Accessory pigments—pass their excited electrons to cholorphyll
• Passes excited electrons to first step of ETC, primary electron acceptor
Term
Photosystems
Definition
• Series of electron transport chains that photosynthesis uses to harness energy from excited electrons
• Have proteins and pigments like chlorophyll
• Use cytochrome complex to pass electrons
• As electrons passed, water broken into oxygen/hydrogen and H+ concentration gradient builds  ATP
• Other elctron transport chain uses NADP+
• End of transport chains, NADP+ receives the electron  NADPH
Term
Dark Reactions
Definition
• Energy from light reactions harnessed  sugar molecules like glucose
• Happen in stroma of chloroplast
• Only rely on NADPH and ATP  don’t need sunlight  “dark” reactions
• Biggest part is Calvin Cycle
Term
Calvin Cycle
Definition
• Primary component of dark reactions
• Cyclical
• Takes carbon in  organic molecule, opposite of Krebs cycle
• Oxygen from CO2 combined with hydrogen to make water
• Diagram on page 91
• ATP and NADPH  NADP+ and glyceraldehyde-3-phosphate molecules
o Some help make glucose and such, some go back to the cycle to make more ribulose
• 3 CO2 + 9 ATP + 6 NADPH  glyceralhedyde-3-phosphate + 12 H2O
Term
Rubsico
Definition
• Protein that converts gaseous carbon into solid carbon
• Crucial part of Calvin cycle
• CO2  5-carbon ribulose biphosphate  6-carbon intermediate sugar  two 3-carbon sugars
• Has to do this three times for every three-carbon sugar from Calvin cycle
• Some plants use PEP carboxylase instead, which is more efficient
Term
CAM Plants
Definition
• Separate times when two reactions of photosynthesis take place
• Only open stroma at night so that they can take in CO2 without water evaporating
• Light reactions during the day  ATP and NADPH; dark reactions at night
Term
Anaerobic
Definition
• Conditions where there is no oxygen present
•  fermentation
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