CELL CHEMISTRY IVProteins & Nucleic Acids

Plasma proteins that you must knowDeoxyribonucleic acid (DNA)

Ribonucleic acids (RNAs)

Significance of Proteins in Physiology

• They are responsible for the unique structure and specific functions of cells

• They function as– Enzymes– Chemical messengers (hormones & neurotransmitters)– Carriers/Transporters (in blood and in cells) – Channels (in cell membranes)– Receptors for hormones & neurotransmitters – Immunity (vaccination)

Know These Proteins and Their Respective Function!

• Hemoglobin:– Transports O2; Inside red blood cells; binds O2 reversibly

• Lactase:– Catalyzes hydrolysis of lactose into --- (what products?)

• Carbonic anhydrase:– Catalyzes synthesis of H2CO3 from CO2 and H2O

• Actin and Myosin:– For muscle contraction and relaxation; Interaction between these two generates forces that

cause movement• Albumin:

– Most abundant protein in plasma; Major role in plasma oncotic (or osmotic pressure)• Immunoglobulins (Ig) G, E

– Also called antibodies; Immunity (as in vaccination) and allergic reaction (IgE)• Keratin:

– Structural protein in cells, nails, hair• Ferritin:

– Intracellular storage of iron

Some Facts on Proteins

• They are polymers of amino acids that are joined by peptide bonds.

• Each protein has a specific or unique amino acid sequence (AAS)

• The AAS determines the 3D structure and the function/s of a protein

• Questions– Peptide bonds are formed by what type of chemical

reaction ---?– What enzyme catalyzes the synthesis of peptide bonds?– What organelle has this enzyme?

More Facts About Proteins

• 3D structure that is maintained by hydrogen bonds and ionic bonds

• Function/s depend on 3D structure• Can be denatured (Denaturation) by

– A) extremes of pH– B) heat

• Questions:– Would denaturation affect the properties, structure and function

of a protein?– An example of denaturation in your kitchen?

Hemoglobin: 3D Structure

• Notice 4 proteins interact to form a single structure (a quarternary structure).

• Hemoglobin is a multimeric protein

• What type of bonds stabilize the “globular” shape of hemoglobin?

Some More Facts About Proteins

• There are thousands of proteins inside a cell• To synthesize proteins, cells need information

from a gene (genetic information)• A Gene is a sequence of nucleotides that has

information for the synthesis of a functional RNA or for a protein. in DNA molecule.

• The nucleotide sequence in a gene dictates the amino acid sequence of the protein or nucleotide sequence of functional RNA encoded in the gene

Protein SynthesisStudy/Review Guyton Ch. 3

• To synthesize proteins, cells need:– Genetic information (Gene)– mRNA, tRNA– Ribosomes– Amino acids (20 different)– Energy

• The key events that you MUST review in any textbook of biology or college Anat & Physiol or in Guyton:1. Transcription (RNA synthesis)2. Translation (protein synthesis)3. Replication (DNA synthesis)

Flow of Genetic information(Guyton Ch. 3)

• In all cells, the flow of genetic information is from: – Gene --> mRNA --> Protein

• Transcription– The enzyme RNA polymeraze catalyzes the synthesis of

phosphodiester bond between ribonucleotides.– The enzyme uses one of the two DNA strands as a template– Notice that DNA IS NOT CONVERTED TO RNA

• Questions• Given the nucleotide sequence: …-T A C G A A C C G A T-…

1. Write the sequence of the complementary strand?2. These two strands would be held together by what bonds?3. Assuming that the bottom strand (answer to #1 is the gene), write

the sequence of the transcribed mRNA?

Nucleic Acids

Some Facts plus Some Illustrations

Nucleic Acids• The nucleic acids are DNA and RNA• DNA is found in the nucleus and mitochondria• RNA is found in the cytoplasm• There are several types of RNA

– mRNA (m = messenger)– rRNA (r = ribosomal)– tRNA (t = transfer)

• They are all Polymers of nucleotides joined by ---? formed by what type of reaction?

Composition of Nucleotide

RNAs: Function of Each

• mRNA is a copy of the information in the gene.• tRNAs, in collaboration with ribosomes, translate

the message in the mRNA. Notice that during protein synthesis, a sequence of ribonucleotides is translated into a sequence of amino acids.– Each codon (a set of 3 consecutive ribonucleotides) of

the mRNA is a code for one amino acid in the protein. • rRNAs are structural component of ribosomes. They

function as enzymes (ribozymes) that catalyze the formation of peptide bonds.

Be Able to Distinguish Amino Acid from Nucleotide

DNA: Composition & Structure (1)

DNA vs RNA (1)

• DNA– Found in the nucleus and mitochondria– Double stranded and shaped as twisted ladder– Contains the pentose deoxyribose– Contains the nucleotides A, T, G, C– In the double strand, A is structurally

complementary to T and G is complementary to C (A:::T, G:::C)

– RNA

DNA: Composition & Structure (2)

RNA vs DNA (2)

• RNA – Found in cytoplasm (cytosol, ribosomes)– Is single stranded– Contains the pentose ribose– Contains the nucleotides A, U, G, C– During transcription, DNA strand serves as

template for RNA synthesis and A is complementary to U, G is complementary to C. (A:::U, G:::C)

Some Questions ??• Given the ….-5’-ACGTCACTCAGTGGATCA-….

1. Write the sequence of the complementary strand

• Assume that the 3’- strand (answer to 1 above) is the gene.

1. What is the sequence of the mRNA from that gene?2. How many codons are there in that (#2) mRNA?3. Write each codon on a separate line in your notes and for each

codon, write the sequence of the corresponding anticodon4. Which RNA has anticodons?5. What is the function of these RNAs (answer to #5) RNAs 6. According to the genetic code (consult Guyton Table 3.1), what is the

amino acid sequence of the peptide from that gene?