The Structure and Func.on of Macromolecules Nucleic Acids

The Structure and Func.on of Macromolecules Nucleic Acids

The FOUR Classes of Large Biomolecules All living things are made up of four classes of large biological molecules: Carbohydrates Lipids Protein Nucleic Acids Macromolecules are large molecules composed of thousands of covalently bonded atoms Molecular structure and function are inseparable 2

A C G T A T G A C C A T G

KP2: Nucleic acids store gene4c material for organisms Monomer: Nucleotide Use: On its own, nothing. EX: Adenine, thymine, Polymer: Nucleic acid Use: Nucleic acids store, transmit, and help express hereditary information and make up genes EX: DNA and RNA 4

Two Types of Nucleic Acids There are two types of nucleic acids Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) DNA provides directions for its own replication DNA directs synthesis of messenger RNA (mrna) and, through mrna, controls protein synthesis Protein synthesis occurs on ribosomes 5

Figure 5.25-1 DNA 1 Synthesis of mrna mrna NUCLEUS CYTOPLASM

Figure 5.25-2 DNA 1 Synthesis of mrna mrna NUCLEUS CYTOPLASM 2 Movement of mrna into cytoplasm mrna

Figure 5.25-3 DNA 1 Synthesis of mrna mrna NUCLEUS CYTOPLASM 2 3 Movement of mrna into cytoplasm Synthesis of protein mrna Ribosome Polypeptide Amino acids

When does a cell copy DNA? When in the life of a cell does DNA have to be copied? cell reproduction mitosis gamete production meiosis

DNA replication It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. James Watson Francis Crick 1953

Watson and Crick and others 1953 1962

Maurice Wilkins and 1953 1962

Rosalind Franklin (1920-1958)

The Components of Nucleic Acids Each nucleic acid is made of monomers called nucleotides Each nucleotide consists of a nitrogenous base, a pentose sugar, and one or more phosphate groups 14

Figure 5.26ab 5ʹ end Sugar-phosphate backbone 5ʹC 3ʹC Nucleoside Nitrogenous base 5ʹC 5ʹC 3ʹC 3ʹ end (a) Polynucleotide, or nucleic acid Phosphate group (b) Nucleotide 3ʹC Sugar (pentose) 1ʹC

Figure 5.26c Nitrogenous bases Pyrimidines Cytosine (C) Thymine (T, in DNA) Uracil (U, in RNA) Purines Sugars Adenine (A) Guanine (G) Deoxyribose (in DNA) Ribose (in RNA) (c) Nucleoside components

The Devil is in the Details There are two families of nitrogenous bases Pyrimidines (cytosine, thymine, and uracil) have a single six-membered ring Purines (adenine and guanine) have a sixmembered ring fused to a five-membered ring In DNA, the sugar is deoxyribose; in RNA, the sugar is ribose 18

The Devil is in the Details Adjacent nucleotides are joined by covalent bonds that form between the OH group on the 3ʹ carbon of one nucleotide and the phosphate on the 5ʹ carbon on the next These links create a backbone of sugar-phosphate units with nitrogenous bases as appendages The sequence of bases along a DNA or mrna polymer is unique for each gene 19

Nucleic Acids Are Informational Macromolecules Nucleotides bond in condensation reactions to form phosphodiester bonds. The linkage is between the #5 carbon of one ribose and the #3 carbon of the next ribose. Nucleic acids grow in the 5 to 3 direction.

Linking Nucleotides Together

Nucleic Acids Are Informational Macromolecules Oligonucleotides have up to 20 monomers. Example: small RNA molecules important for DNA replication and gene expression. DNA and RNA are polynucleotides, the longest polymers in the living world.

The Devil is in the Details RNA molecules usually exist as single polypeptide chains DNA molecules have two polynucleotides spiraling around an imaginary axis, forming a double helix In the DNA double helix, the two backbones run in opposite 5ʹ 3ʹ directions from each other, an arrangement referred to as antiparallel One DNA molecule includes many genes 23

The Devil is in the Details The nitrogenous bases in DNA pair up and form hydrogen bonds: adenine (A) always with thymine (T), and guanine (G) always with cytosine (C) Called complementary base pairing Complementary pairing can also occur between two RNA molecules or between parts of the same molecule In RNA, thymine is replaced by uracil (U) so A and U pair 24

Complementary base pairing:

Base pairs are linked by hydrogen bonds, favored by the arrangement of polar bonds in the bases. There are so many hydrogen bonds in DNA and RNA that they form a fairly strong attraction, but not as strong as covalent bonds. Thus, base pairs can be separated with only a small amount of energy.

In RNA, the base pairs are A U and C G. RNA is usually single-stranded, but may be folded into 3-D structures by hydrogen bonding. Folding occurs by complementary base pairing, so structure is determined by the order of bases.

RNA The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

5ʹ 3ʹ Sugar-phosphate backbones The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. Hydrogen bonds Base pair joined by hydrogen bonding 3ʹ (a) DNA 5ʹ Base pair joined by hydrogen bonding (b) Transfer RNA

DNA is usually double stranded. Two polynucleotide strands form a ladder that twists into a double helix. Sugar-phosphate groups form the sides of the ladder, the hydrogen-bonded bases form the rungs.

Figure 3.4 DNA

Interes4ng note Ra4o of A-T:G-C affects stability of DNA molecule 2 H bonds vs. 3 H bonds biotech procedures more G-C = need higher T to separate strands high T organisms many G-C parasites many A-T (don t know why)

Another interes4ng note ATP Adenosine triphosphate u modified nucleo.de adenine (AMP) + P i + P i + +

The two strands are antiparallel (running in opposite directions), and the double helix is right-handed.

DNA s information is encoded in the sequence of bases. DNA has two functions: Replication Information is copied to RNA and used to specify amino acid sequences in proteins.

DNA replication and transcription depend on base pairing: 5 -TCAGCA-3 3 -AGTCGT-5 transcribes to RNA with the sequence 5 -UCAGCA-3.

DNA replication: the entire molecule must be replicated completely so that each new cell receives a complete set of DNA. Genome complete set of DNA in a living organism Genes DNA sequences that encode specific proteins and are transcribed into RNA

Gene expression: transcription and translation of a specific gene. Not all genes are transcribed in all cells of an organism.

DNA Replication and Transcription

DNA base sequences reveal evolutionary relationships. Closely related living species should have more similar base sequences than species that are more distantly related. Scientists are now able to determine and compare entire genomes of organisms to study evolutionary relationships.

Link to Evolu4on The linear sequences of nucleotides in DNA molecules are passed from parents to offspring Two closely related species are more similar in DNA than are more distantly related species Molecular biology can be used to assess evolutionary kinship 42

Polymers and their linkages 43

Guide Prac4ce PoL GR Ac4ve Learning Exercise McMillan Ac4ve learning Exercise 44