Anatomy and Physiology 12 - DNA, Protein Synthesis

Anatomy and Physiology 12 UNIT 3: DNA, Protein synthesis, Metabolism and Enzymes  UNIT A Chapter 4: DNA Structure and Gene Expression Section 4.1 DNA Structure Determining that DNA is the genetic material was accomplished through decades of...

Anatomy and Physiology 12 UNIT 3: DNA, Protein synthesis, Metabolism and Enzymes  UNIT A Chapter 4: DNA Structure and Gene Expression Section 4.1 DNA Structure Determining that DNA is the genetic material was accomplished through decades of research by many scientists. In the late 1920s, Frederick Griffith’s studies identified a transforming substance that could change nonlethal bacteria to lethal bacteria. gr-12-button.jpg TO PREVIOUS Figure 4.1 Griffith’s experiment. SLIDE  UNIT A Chapter 4: DNA Structure and Gene Expression Section 4.1 The Nature of Genetic Material In the early 1950s, Hershey and Chase firmly established DNA as the genetic material. They used a virus (T phage) that infects bacteria, where it makes new copies of itself. In one experiment, they used virus with radioactive DNA and identified where the radioactivity went after infection gr-12-button.jpg Figure 4.2a Hershey-Chase experiments. TO PREVIOUS SLIDE  UNIT A Chapter 4: DNA Structure and Gene Expression Section 4.1 In another experiment, they used a virus with radioactive protein and identified where the radioactivity went after infection. They discovered that radioactivity entered the bacterial cells when virus with radioactive DNA was added, but not virus with radioactive protein. Therefore, the hereditary material is DNA Figure 4.2b Hershey-Chase experiments. What is DNA? DNA stands for Deoxyribonucleic acid DNA is the genetic material and the control molecule of life. DNA has three major functions: 1. DNA CONTROLS CELLULAR ACTIVITIES, including reproduction. – DNA carries a CODE. Genetic instructions are encoded in the sequence of bases strung together in DNA. – DNA from male and DNA from female together become the genetic information of offspring in sexual reproduction. 2. DNA MAKES EXACT COPIES OF ITSELF to pass onto other cells. – DNA does this through a process called “replication.” 3. DNA UNDERGOES MUTATIONS – mutations and re-combinations in the structure and number of DNA molecules are the source of life's diversity. – Evolution, in essence, proceeds from the level of DNA. Different combinations of DNA sequences due to mutations and sexual reproduction explain the existence of all the different species that have lived on this Earth. DNA is the source of the unity of life Life began as a nucleic acid. (recall that there are TWO Types of Nucleic acids: DNA & RNA). The first form of life on this planet is thought by many biologists to be a self-replicating strand of RNA.  UNIT A Chapter 4: DNA Structure and Gene Expression Section 4.1 Structure of DNA DNA is a chain of nucleotides Each nucleotide consists of a phosphate group, a deoxyribose sugar, and a nitrogen-containing base There are four bases: two purines, adenine (A) and guanine(G), and two pyrimidines, cytosine (C) and thymine (T) gr-12-button.jpg TO PREVIOUS Figure 4.3c Overview of DNA structure. SLIDE  UNIT A Chapter 4: DNA Structure and Gene Expression Section 4.1 Structure of DNA A DNA strand has a backbone of alternating phosphate and sugar molecules Two DNA strands twist about each other, forming a double helix Purines and pyrimidines on opposite strands form hydrogen bonds in complementary base pairing (A-T, G-C) gr-12-button.jpg TO PREVIOUS Figure 4.3a and b Overview of DNA structure. SLIDE DNA strands are extremely long Each one containing millions of atoms. Every human cell contains about one meter of these twisted strands (this amounts to about 4 billion pairs of bases). Only about 3 million base pairs are responsible for the differences among us — which is only one tenth of 1% of our DNA. Yet these DNA base sequence variations influence most of our physical differences and many of our other characteristics, as well. GENES AND CHROMOSOMES GENES are the units of inheritance that control characteristics or capabilities of an organism. Genes are located on the chromosomes of the cell nucleus and consist of segments of DNA molecules. A gene consists of a sequence of about 1000 DNA base-pairs (though there is considerable variation in this length). About 175,000 genes compose the DNA molecule of a single human chromosome. The genes act in pairs that dictate traits. Genes control cellular chemical reactions, by directing the formation of enzymes. Genes always occur in pairs. Half of each person's genes come from the mother and half from the father. Most ordinary characteristics like height and eye color are determined by combinations of several different genes Numbers of Chromosomes Karyotyping Sex chromosome - XY CHROMOSOME Y ☺  UNIT A Chapter 4: DNA Structure and Gene Expression Section 4.2 DNA Replication When cells divide, each new cell requires a copy of the DNA. DNA replication Is the copying of one double helix into two identical double helices, which are also identical to the original Is semi-conservative (each new double helix has one original strand and one newly synthesized strand) gr-12-button.jpg TO PREVIOUS Figure 4.4 Overview of DNA Replication SLIDE  UNIT A Chapter 4: DNA Structure and Gene Expression Section 4.2 Replication at the Molecular Level 1. DNA helicase enzyme separates the DNA strands by breaking the hydrogen bonds between bases. 2. DNA polymerase enzyme catalyzes incorporation of new nucleotides by complementary base pairing. 3. DNA polymerase can only add nucleotides to one end of the growing chain. Therefore, replication is different for each strand. Leading strand synthesis follows the helicase enzyme. Lagging strand synthesis results in formation of Okazaki fragments. 4. DNA ligase connects the Okazaki fragments and seals any breaks in the sugar-phosphate backbone. gr-12-button.jpg TO PREVIOUS SLIDE UNIT A Chapter 4: DNA Structure and Gene Expression Section 4.2 Replication at the Molecular Level Figure 4.5 Molecular mechanisms of DNA replication. The major enzymes gr-12-button.jpg involved in DNA replication. Note that the synthesis of the new DNA molecules occurs in opposite directions due to the orientation of the original DNA strands. TO PREVIOUS SLIDE RNA: RIBONUCLEIC ACID: how DNA communicates its message. RNA is the genetic material of some viruses and is necessary in all organisms for protein synthesis to occur. RNA could have been the “original” nucleic acid when life first arose on Earth some 3.8 billion years ago. RNA Differences between DNA & RNA 1. Uracil used instead of Thymine 2. Sugar in RNA is RIBOSE (not deoxyribose) H3C O H N H 2 O N 5' O O- P O CH2 O O- H H H H 3' OH H 3. RNA is SINGLE-STRANDED, unlike DNA which is double stranded. RNA, therefore, is not a double helix. RNA is much shorter than DNA. 4. RNA is made from DNA through a process called Transcription. Comparison of DNA and RNA