CHAPTER 4 A&P: CELLULAR METABOLISM

metabolism

sum of all chemical reactions in the body

cellular metabolism

sum of all chemical reactions occurring in a cell; metabolic reactions usually occur in pathways or cycles

what are the 2 types of metabolic reactions?

anabolism and catabolism

anabolism

small molecules are built into larger ones; requires energy

catabolism

larger molecules are broken down in to smaller ones; releases energy

what occurs in anabolism?

• provides materials for maintenance, cellular growth and repair

• requires ATP made during catabolism

• ex. dehydration synthesis

• smaller molecules are bound together to form larger ones

• water is produced in the process

• used to produce polysaccharides, proteins, and triglycerides

what occurs in catabolism?

• breaks down larger molecules into smaller molecules

• ATP is produced

• ex. hydrolysis

• used to decompose carbohydrates, proteins, and lipids

• uses water to split the substances

• reverse of dehydration synthesis

what is the purpose of enzymes?

• control rates of both catabolic and anabolic reactions

• greatly increase reaction rates

enzymes (protein catalysts)

• globular proteins that catalyze specific reactions

• increases rates of chemical reactions

• lower the activation energy necessary to start reactions

• not consumed in the reaction, so they are used repeatedly

• each is specific to a specific substrate

• ability to recognize substrate depends on shape of active site of enzymes

• many enzymes are named after substrate, with “ase”

what are metabolic pathways?

• series of enzyme-controlled reactions leading to formation of a product

• each new substrate is the product of the previous reaction

• each step of a pathway is catalyzed by a different enzyme

what do rate limiting enzymes do?

• a regulatory enzyme that catalyzes one step of pathway typically sets rat for entire reaction sequence

• number of molecules of this enzyme is limited

• often the enzyme in the reaction sequence

• in some pathways, end product inhibits rate-limiting enzymes; this is an example of negative feedback

what are three factors that alter enzymes?

cofactor, coenzymes and denaturation

cofactor

• non-protein substance that combines with the enzymes to activate it

• some help fold active site into proper conformation

• some help bind enzymes to substrate

• can be ion, element, or small organic molecules (coenzymes)

coenzymes

• organic molecule that acts as cofactor

• most are vitamins, which are essential organic molecules that humans must get from their diet

denaturation

• inactivation of an enzyme (or any other protein), due to an irreversible change in its conformation

• results in enzyme being unable to bind to substrate

• can be caused by radiation, excess heat exposure, extreme pH values, electricity, and particular chemicals

energy

• capacity to change something, or the ability to do work

• common forms of energy: heat, light, sound, electrical energy, mechanical energy, chemical energy

• energy cannot be created or destroyed, but can be changed from one form to another

cellular respiration

• process that transfers energy from molecules, and makes it available for cellular use

• most metabolic reactions use chemical energy

how is energy released?

energy is held in chemical bonds, and released when bonds are broken

what is the distribution of energy transferred in ATP?

• 40% is released as chemical energy

• 60% is released as heat; maintains body temperature

ATP molecules

• molecules that carries energy in a form the cell can use

• main energy-carrying molecule in the cell; energy from ATP breakdown is used for cellular work

• consists of 3 portions: adenine, ribose (a sugar), and 3 phosphates in a chain

• second and third phosphate are attached by high-energy bonds; energy can be quickly transferred to other molecules

ADP molecules

when ATP loses terminal phosphate, it becomes Adenosine Diphosphate (ADP)

phosphorylation

• ADP can be converted back into ATP by attaching a third phosphate

• requires energy from cellular respiration

• ATP and ADP cycle back and forth between cellular respiration and energy-utilizing reactions

what processes are a part of cellular respiration?

• glycolysis (anaerobic)

• citric acid cycle (aerobic)

• electron transport chain/ oxidative phosphorylation (aerobic)

• glycolysis and ETC are stepwise reaction sequences

• citric acid cycles occur in a metabolic cycle in which the final product reacts to replenish original substrate

what occurs in cellular respiration?

• cellular respiration of glucose requires a supply of glucose and O2.

• the final products of cellular respiration are carbon dioxide, water, ATP (chemical energy, 40%) and heat (60%)

• anerobic reactions: do no require o2 and make little ATP

• aerobic reactions: require O2, and make most of ATP

glycolysis

• first reaction sequence of glucose breakdown

• series of 10 reactions

• breaks down glucose (6-carbon) into 2 pyruvic acid (3-carbon) molecules

• occurs in cytosol

• anaerobic phase of cellular respiration

• yield 2 ATP molecules per glucose molecule broken down

• 3 phases: phosphorylation of glucose; splitting/cleavage of glucose into two 3-carbon molecules; production of NADH, ATP, and 2 molecule of pyruvic acid

what occurs in anaerobic reactions?

• in presence of O2, NADH and H+ deliver hydrogen atoms to the electron transport chain, with oxygen as final electron acceptor

• in absence of O2, there is no electron acceptor

• NADH and H+ deliver electrons ad H+ back to pyruvic acid, to form lactic acid

• buildup of lactic acid inhibits glycolysis

• ATP production is decreased

• glycolysis produces much less ATP than aerobic respiration

• there is net gain of 2 ATP per molecules of glucose broken down

what occurs in aerobic reactions?

• in presence of O2, pyruvic acid enters aerobic pathways

• includes synthesis of acetyl coenzyme A, citric acid cycle, and electron transport chain

• begins with pyruvic acid moving from cytosol to mitochondria

• pyruvic acid is used to produce Acetyl CoA

• end products are CO2, H2O, and up to 36 ATP per molecule of glucose

what occurs in the citric acid cycle?

• begins when acetyl CoA combines with oxaloacetic acid to produce citric acid

• citric acid is changed into oxaloacetic acid through a series of reactions

• cycle repeats as long as pyruvic and O2 are available

• for each citric acid molecule: 1 ATP is produced, 8 hydrogens atoms are transferred to NAD+ and FAD, 2 CO2 are produced, enters blood and is exhaled

what occurs in the electron transport chain?

• NADH and FADH2 carry hydrogen and high-energy electrons

• ETC is a series of enzyme complexes (electron carriers) located in the inner membrane of mitochondria

• energy from electrons is transferred to the enzyme ATP synthase

• ATP synthase used energy to catalyze phosphorylation of ADP to ATP

• H2O is formed (oxygen is in the final electron “carrier”)

• summary of ATP production in complete oxidation of glucose: 2 ATP produced in glycolysis, 2 ATP in citric acid cycle, and 28 in electron transport chain

where are carbohydrate stored?

• carbohydrate molecules from food can: enter catabolic pathways for energy production and enter anabolic pathways for storage

• react to form some amino acids

• excess glucose can be converted into stores as:

• glycogen: most cells, but liver and muscle cells store the most

• fat: for storage in adipose tissue

DNA (deoxyribonucleic acid)

• the genetic material

• molecule that stores information on its sequence of nucleotides, that instructs a cell to how synthesize certain proteins

• the proteins coded for on DNA function as: enzymes, blood proteins, structural proteins of muscle and connective tissue, antibodies, and cell membrane components

genetic information

instructions to tell cells how to construct proteins; stored in DNA sequence

gene

sequence of DNA that contains information for making 1 protein

genome

complete set of genetic information in a cell

exome

small portion of the genome that codes for proteins

gene expression

control of which proteins are produced in each cell type, in what amount, and under which circumstances

what is the structure of DNA composed of?

double helix:

- double stranded molecule, consisting of 2 chains of nucleotides

-dna resembles ladder twisted into a spiral

-backbone of each strand is a sugar-phosphate chain

bases from the 2 complementary strands are linked together by hydrogen bonds: CGAT

nucleotides:

-are building blocks of DNA, consists of a 5-carbon sugar deoxyribose, phosphate group, a nitrogenous base (adenine, cytosine, guanine, or thymine)

DNA replication

process that produces an exact copy of DNA molecule; occurs during interphase

what are the steps in DNA replication?

• hydrogen bonds break between base pairs

• strands unwind and separate

• new nucleotides pair with exposed bases, under directions of DNA polymerase

• other enzymes connect new sugar-phosphate backbone

protein synthesis

• a sequence of 3 DNA nucleotides provide template for complimentary RNA

• each unit of 3 RNA nucleotides represents genetic code

• sequence of bases in a gene determines the amino acid sequences in a polypeptide

• each sequence of 3 nucleotides either represents an amino acid or signals to begin or end protein synthesis

• there are 20 amino acids that are used to synthesize our proteins

• protein synthesis involves the enzyme-catalyzed processes of transcription and translations

RNA molecules

RNA differs from DNA in following ways:

-single strand of nucleotides instead of double helix

-contains the sugar, ribose, instead of deoxyribose

-one of the nucleotide bases is different: RNA contains Uracil, but the other 3 bases are the came (A, G, and C)

-much shorter than DNA

-there are different types of RNA: messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA)

what occurs in transcription?

• DNA (deoxyribonucleic acid) stores master copy of genetic code, and remains in the nucleus

• protein synthesis occurs in cytoplasm

• RNA (ribonucleic acid) copies and transfers information from DNA to cytoplasm

• transcription: process of copying a specific DNA sequence onto an RNA sequence

• Messenger RNA (mRNA): the type of RNA that carries genetic code from DNA to ribosomes in cytoplasm

• RNA polymerase: enzyme that catalyzes the formation of mRNA from the proper strand of DNA

what are the steps in transcription?

• RNA polymerase recognizes correct strand of DNA to copy

• RNA polymerase binds to Promoter, the DNA sequence that signals beginning of a gene

• a section of DNA unwinds to expose the gene coding for the particular proteins

• complementary mRNA nucleotides pair with the DNA bases

• termination signal indicates end of gene

• new mRNA strand is released, and DNA rewinds into double helix

• the mRNA new leaves the nucleus through a nuclear pore, and attaches to a ribosomes in the cytoplasm

what occurs in translation?

• each amino acid is specified by a sequence of 3 bases in DNA, called codons

• protein synthesis occurs in cytoplasm

• mRNA leaves nucleus and binds to ribosome, to act as template for protein synthesis

• at the ribosome, the genetic code, carried by mRNA, is used to synthesize a protein

• translation: process of converting the genetic code, carried by mRNA, into a sequence of amino acids that becomes a protein

what are the steps in translation?

• protein synthesis requires that amnio acids are added to growing polypeptide chain in proper sequence

• Transfer RNA (tRNA) aligns amnio acids during translation, along the mRNA strand on the ribosome

• tRNA binds to its amino acid, transport it to a ribosome, binds to the mRNA according to its sequence, and adds its amino acid to the growing polypeptide chain

• each tRNA contains a sequence of 3 nucleotide bases, the anticodons, which binds to the complementary codon on the mRNA strand

• as the ribosome moves down mRNA, each tRNA bring in its amino acid to be added to the growing protein

ribosomes in translation

• organelles composed of ribosomal RNA (rRNA) and protein molecules

• composed of 2 unequal subunits

• binding to tRNA and mRNA occurs in association with a ribosome

• ribosomes moves down mRNA molecule, bringing in tRNAs carrying the proper amino acids to add to the growing protein chain

• amino acids are joined by peptide bonds

• when ribosome reaches a “stop” codon, the protein is released

• ribosomes, mRNA, and rRNA can be used repeatedly

what causes change in genetic information?

• 99.9% of human genome sequences are the same among all people

• 0.1% of the genome that varies among people includes: DNA sequences that affect health, appearance, and base variations that have no observable effects

mutations

changes in the DNA sequence due to errors in DNA replication

when doe mutations occur?

-occurs when bases are changed, added or deleted

-spontaneous: due to insertion of unstable base into DNA sequence

-induced: due to exposure to mutagen's, chemicals or radiation that cause mutation