Chapter 12

Question 1

Anabolism

Answer 1

Energy from catabolism is used for biosynthetic pathways
using a carbon source and inorganic molecules, organisms synthesize new organelles and cells
antibiotics inhibit anabolic pathways
a great deal of energy is needed for anabolism

Question 2

Anabolism 2

Answer 2

Turnover
continual degradation and resynthesis of cellular constituents by nongrowing cells
Metabolism is carefully regulated
for rate of turnover to be balanced by rate of biosynthesis
in response to organism’s environment

Question 3

Precurser metabolites

Answer 3

Generation of precursor metabolites is critical step in anabolism
Carbon skeletons are used as starting substrates for biosynthetic pathways
examples are intermediates of the central metabolic pathways
most are used for the biosynthesis of amino acids

Question 4

heterotrophs

Answer 4

exogenous organic source, or can sometimes synthesize it from other organic molecules

Question 5

autotrophs and chemolithotrophs

Answer 5

synthesize glucose from CO2 via the Calvin Cycle (or other)

Question 6

gluconeogensis

Answer 6

synthesis of glucose from other molecules
Synthesis of glucose from phosphoenolpyruvate
Phosphoenolpyruvate can be synthesized from oxaloacetate

Question 7

Calvin cycle

Answer 7

Used by most autotrophs to fix CO2
Also called the reductive pentose phosphate cycle
In eukaryotes, occurs in stroma of chloroplasts
In cyanobacteria, some nitrifying bacteria, and thiobacilli, may occur in carboxysomes
inclusion bodies that may be the site of CO2 fixation
Consists of 3 phases
the carboxylation phase
the reduction phase
the regeneration phase
Three ATPs and two NADPHs are used during the incorporation of one CO2
Takes a total of 18 ATP and 12 NADPH for one glucose

Question 8

Carboxylation phase

Answer 8

Catalyzed by the enzyme ribulose 1.5-bisphosphate carboxylase, also called ribulose bisphosphate carboxylase/oxygenase (rubisco)
Rubisco catalyzes addition of CO2 to ribulose-1,5-bisphosphate (RuBP), forming 2 molecules of 3-phosphoglycerate

Question 9

Reduction and Regeneration Phases

Answer 9

3-phospho-glycerate reduced to glyceraldehyde 3-phosphate
RuBP regenerated
Carbohydrates (e.g., fructose and glucose) are produced

Question 10

The hydroxypropionate bi-cycle

Answer 10

used by some archaeal genera and the green nonsulfur bacteria (also anoxygenic phototrophs)

Question 11

The 3-Hydroxypropionate/4-Hydroxybutyrate Pathway

Answer 11

First described in 2007 in an archeon
Uses 3-hydroxypropionate cycle
Uses unique reaction to produce 3-hydroxybutryate

Question 12

Gluconeogenesis

Answer 12

Synthesis of glucose and related sugars from nonglucose precursors
glucose, fructose, and mannose are gluconeogenic intermediates or made directly from them
galactose is synthesized with nucleoside diphosphate derivatives
bacteria and algae synthesize glycogen and starch from adenosine diphosphate glucose
Functional reversal of glycolysis, but the two pathways are not identical
7 enzymes shared
4 enzymes are unique to gluconeogenesis

Question 13

synthesis of monosaccharides

Answer 13

Several sugars are synthesized while attached to a nucleoside diphosphate such as uridine diphosphate glucose (UDPG)

Question 14

Synthesis of Polysaccharides

Answer 14

Also involves nucleoside diphosphate sugars
e.g., starch and glycogen synthesis

ATP + glucose 1-P  ADP-glucose + PPi

(glucose)n + ADP-glucose  (glucose)n+1 + ADP

Question 15

Amino acid biosynthesis

Answer 15

Carbon skeletons come from intermediates of glycolysis or citric acid cycle (slide 42)
The amino group typically comes from inorganic nitrogen source obtained from the environment (e.g., NH3) and is incorporated by glutamine dehydrogenase or glutamine synthetase

Question 16

Nitrogen assimilation

Answer 16

Nitrogen addition to carbon skeleton is an important step
potential sources of nitrogen: ammonia, nitrate, or nitrogen from the environment
most cells use ammonia or nitrate
ammonia nitrogen (universal source) easily incorporated into organic material because it is more reduced than other forms of inorganic nitrogen

Question 17

Ammonia Incorporation into Carbon Skeletons

Answer 17

Ammonia N can be directly assimilated by
transaminase activity from one aa to another
glutamate dehydrogenase
glutamine synthetase-glutamate synthase systems
Once incorporated, nitrogen can be transferred to other carbon skeletons by transaminases

Question 18

Assimilatory nitrate reduction

Answer 18

Used by bacteria to reduce nitrate to ammonia and then incorporate it into an organic form
Nitrate reduction to nitrite catalyzed by nitrate reductase
Reduction of nitrite to ammonia catalyzed by nitrite reductase

Question 19

nitrogen fixation

Answer 19

Reduction of atmospheric nitrogen to ammonia
Catalyzed by nitrogenase
found only in bacteria and archaea

Question 20

Mechanism of nitrogenase activity

Answer 20

Occurs in 3 steps to reduce N2 to 2 molecules of NH3
Requires large ATP expenditure
Once reduced, NH3 can be incorporated into organic compounds

Question 21

sulfar assimilation

Answer 21

Sulfur needed for
synthesis of amino acids cysteine and methionine
synthesis of several coenzymes
Sulfur obtained from
external sources
intracellular amino acid reserves (-SH)

sulfate = main (universal) inorganic sulfur source
assimilatory sulfate reduction
sulfate reduced to H2S and then used to synthesize cysteine
cysteine can then be used to form sulfur containing organic compounds

Question 22

purines

Answer 22

cyclic nitrogenous bases consisting of 2 joined rings

adenine and guanine

Question 23

pyrimidines

Answer 23

cyclic nitrogenous bases consisting of single ring

uracil, cytosine, and thymine

Question 24

nucleoside

Answer 24

nitrogenase base pentose sugar

Question 25

nucelotide

Answer 25

nucleoside phosphate

Question 26

phosphorus assimilation

Answer 26

Phosphorus found in nucleic acids as well as proteins, phospholipids, ATP, and some coenzymes
Most common phosphorus sources are inorganic phosphate (universal) and organic phosphate esters .
Inorganic phosphate (Pi)
incorporated through the formation of ATP by
photophosphorylation
oxidative phosphorylation
substrate-level phosphorylation
Organic phosphate esters
present in environment in dissolved or particulate form
hydrolyzed by phosphatases, releasing Pi

Question 27

Purine biosynthesis

Answer 27

Complex pathway in which several different molecules contribute parts to the final purine skeleton
Initial products are ribonucleotides
Deoxyribonucleotides formed by reduction of nucleoside diphosphates or nucleoside triphosphates

Question 28

pyrimidine biosynthesis

Answer 28

Begins with aspartic acid and high energy carbamoyl phosphate
Ribonucleotides are initial products
Deoxy forms of U and C nucleotides formed by reduction of ribose to deoxyribose

Question 29

lipid synthesis

Answer 29

Lipids
major required component in cell membranes
most bacterial and eukaryal lipids contain fatty acids

Question 30

fatty acids

Answer 30

Synthesized from acetyl-CoA, malonyl-CoA, and NADPH by fatty acid synthase system
During synthesis the intermediates are attached to the acyl carrier protein
Double bonds can be added in two different ways

Question 31

triglycerols and phspholipids

Answer 31

Eukaryotic microbe and a few gram-positive bacteria can store carbon and energy as triacylglycerol
Made from fatty acids and glycerol phosphate
Phosphatidic acid is an important intermediate in this pathway

Question 32

phospholipids

Answer 32

Synthesized from phosphatidic acid by forming CDP-diacylglycerol, then adding an amino acid