Cellular Metabolism: Anabolism, Catabolism, and DNA

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.

Anabolism

Small molecules are built into larger ones; requires energy

Catabolism

Larger molecules are broken down into smaller ones; releases energy

Dehydration synthesis

Smaller molecules are bound together to form larger ones; H2O produced in the process; used to produce polysaccharides, proteins, triglycerides.

Hydrolysis

Used to decompose carbohydrates, proteins, lipids; uses H2O to split the substances; reverse of dehydration synthesis.

Control of Metabolic Reactions

Rates of catabolism and anabolism must be carefully controlled; breakdown/energy-releasing reactions must occur at rates that balance with build-up/energy-utilizing reactions.

Enzymes

Globular proteins that catalyze specific reactions; increase rates of chemical reactions; lower the activation energy necessary to start reactions.

Enzyme Action

Not consumed in the reaction, so are used repeatedly; each enzyme is specific to a particular substrate.

Active site

Shape of active site of enzyme determines the ability to recognize substrate.

Rate-limiting enzyme

A regulatory enzyme that catalyzes one step of pathway typically sets rate for entire reaction sequence; number of molecules of this enzyme is limited.

Negative feedback

In some pathways, end product inhibits rate-limiting enzyme.

Metabolic Pathways

Series of enzyme-controlled reactions leading to formation of a product; each new substrate is the product of the previous reaction.

Specificity of Enzymes

Many enzymes are named after substrate, with "-ase" as suffix; example: "lipase" breaks down lipids.

Imbalances in reaction rates

Can damage or kill a cell.

Enzyme-catalyzed reactions

Each step of a pathway is catalyzed by a different enzyme.

Energy production in Catabolism

A T P is produced.

Energy requirement in Anabolism

Requires A T P made during catabolism.

Cofactor

Non-protein substance that combines with the enzyme to activate it

Coenzyme

Organic molecule that acts as cofactor

Denaturation

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

Energy

Capacity to change something, or the ability to do work

Common forms of energy

Heat, light, sound, electrical energy, mechanical energy, chemical energy

Cellular respiration

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

Chemical energy

Energy stored in chemical bonds, released when bonds are broken

Oxidation

Releases energy from glucose and other molecules, via loss of hydrogen atoms and their electrons

ATP (Adenosine Triphosphate)

Molecule that carries energy in a form the cell can use

ATP breakdown

Energy from ATP breakdown is used for cellular work

Glycogen

Excess glucose can be converted into and stored as glycogen; most cells, but liver and muscle cells store the most

Fat

Excess glucose can be converted into and stored as fat for storage in adipose tissue

Energy transfer to ATP

40% is released as chemical energy; 60% is released as heat; maintains body temperature

ATP structure

Consists of 3 portions: Adenine, Ribose (a sugar), 3 phosphates in a chain

High-energy bonds in ATP

Second and third phosphates are attached by high-energy bonds; energy can be quickly transferred to other molecules

Metabolic reactions

Most metabolic reactions use chemical energy

Enzymes in cellular respiration

In cells, enzymes lower activation energy needed for oxidation in reactions of cellular respiration

Catabolic pathways

Carbohydrate molecules from foods can enter catabolic pathways for energy production

Anabolic pathways

Carbohydrate molecules from foods can enter anabolic pathways for storage

Amino acids formation

Carbohydrate molecules from foods can react to form some amino acids

DNA (Deoxyribonucleic Acid)

The genetic material that stores information on its sequence of nucleotides, that instructs a cell on how to synthesize certain proteins.

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.

Double helix

Double-stranded molecule, consisting of 2 chains of nucleotides that resembles a ladder twisted into a spiral.

Backbone of DNA

Each strand is a sugar-phosphate chain.

Complementary Base Pairing

Bases pair only with specific pairs: A ̶ T and C ̶ G.

Nucleotides

Building blocks of DNA, consisting of a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, cytosine, guanine, or thymine).

Antiparallel

The 2 nucleotide chains of the double helix point in opposite directions.

Purines

A and G are purines.

Pyrimidines

C and T are pyrimidines.

Histone proteins

DNA wraps around histone proteins to give the double helix a compact form in chromatin and chromosomes.

Hydrogen bonds in DNA

Bases from the 2 complementary strands are linked together by hydrogen bonds: C ̶ G, A ̶ T.

Structural proteins

Proteins coded for on DNA that function as structural proteins of muscle and connective tissue.

Antibodies

Proteins coded for on DNA that function as antibodies.

Cell membrane components

Proteins coded for on DNA that function as components of cell membranes.

Protein Synthesis

A sequence of 3 nucleotides provides template for complementary RNA.

Genetic Code

Each unit of 3 RNA nucleotides represents genetic code.

Gene Sequence

Sequence of bases in a gene determines the amino acid sequence in a polypeptide.

Nucleotide Sequence

Each sequence of 3 nucleotides either represents an amino acid or signals to start or stop protein synthesis.

Transcription

Process of copying DNA sequence onto an RNA sequence.

DNA

Stores master copy of genetic code, and remains in the nucleus.

RNA

Copies and transfers information from DNA to the cytoplasm.

Messenger RNA (mRNA)

The type of RNA that carries genetic code from DNA to ribosome in cytoplasm.

RNA Polymerase

Enzyme that catalyzes the formation of mRNA from the proper strand of DNA.

Codons

Each amino acid is specified by a sequence of 3 bases in DNA, called codons.

Ribosome

Organelles composed of Ribosomal RNA (rRNA) and protein molecules.

Transfer RNA (tRNA)

Aligns amino acids during translation, along the mRNA strand on the ribosome.

Anticodon

Each tRNA contains a sequence of 3 nucleotide bases, the anticodon, which binds to the complementary codon on the mRNA strand.

Amino Acids

There are 20 types of amino acids.

mRNA Codons

There are 64 possible codons (3-base sequences) on mRNA.

Initiation Codon

The Initiation codon, AUG, codes for Methionine and signals the start of a protein.

Stop Codons

3 codons are Stop codons, signaling the end of a protein; these do not have corresponding tRNAs.

Peptide Bonds

Amino acids are joined by peptide bonds.

Ribosome Function

Ribosome moves down mRNA molecule, bringing in tRNAs carrying the proper amino acid to add to the growing protein chain.

Reusability of Ribosomes

Ribosomes, mRNA, and rRNA can be used repeatedly.