DNA - The Code of Life 2024 PDF

# DNA - The Code of Life ## Introduction Nucleic acids are the "molecules of life." They have the ability to store important information which controls cellular activity so that organisms are able to carry out all the basic processes of life. How do they do this? By controlling the synthesis of pr...

# DNA - The Code of Life ## Introduction Nucleic acids are the "molecules of life." They have the ability to store important information which controls cellular activity so that organisms are able to carry out all the basic processes of life. How do they do this? By controlling the synthesis of proteins. There are two different nucleic acids: 1. DNA (deoxyribonucleic acid) 2. RNA (ribonucleic acid) ## Recap Structure of Nucleus The nucleus is a large, round structure that is usually visible in the center of the cell. It is surrounded by a double membrane called the nuclear envelope. The nucleus contains the cell's genetic material, which is organized into chromosomes. The chromosomes are made up of DNA and protein. The DNA molecule contains the instructions for building and maintaining the cell. ## Structure of Nucleic Acids DNA & RNA are referred to as nucleic acids. - Monomers (smallest unit) is called nucleotides - Each nucleotide is made up of: - Nitrogenous base - Sugar portion - Phosphate group ## DNA ### DNA Structure - Deoxyribonucleic acid - DNA in the nucleus --> nuclear DNA - Wrapped around histones (proteins) - DNA outside the nucleus --> extranuclear DNA - Chloroplast --> chloroplastic DNA - Mitochondria --> mitochondrial DNA ### Functions of DNA - Nuclear DNA controls the synthesis of proteins - Enzymes (modified proteins) control metabolic activities in a cell --> DNA controls the structure & functioning of cells - Nuclear DNA transmits hereditary characteristics from parents to offspring. ### Structure of DNA - Made up of nucleotides (monomers) - Sugar - Phosphate - Nitrogenous base - The sugar molecule of DNA is deoxyribose - 2 groups of nitrogenous bases: - Purines (adenine and guanine) - bigger - Pyrimidines (cytosine and thymine) - smaller - The sugar molecule of a nucleotide attaches to the phosphate ion of another by sugar-phosphate bonds --> forming a long chain of sugars and phosphates. - Another chain of nucleotides comes to lie next to this one in such a manner that: - Cytosine always pairs with guanine with 3 H-bonds - Adenine always pairs with thymine with 2 H-bonds - Double-stranded ladder-like DNA structure twists so that 1 strand coils around the other forming a double helix. ### History of the Discovery of DNA - Rosalind Franklin proposed the double helix structure from X-ray diffraction images - Her partner Maurice Wilkins showed these images to James Watson & Francis Crick - Watson & Crick found that DNA contained similar amounts of cytosine and guanine and similar amounts of adenine and thymine: - Complementary base pairs - Allows DNA to make exact copies of itself - Watson & Crick put forward their model of double-helix DNA - James Watson, Francis Crick & Maurice Wilkins --> Nobel Prize ## DNA Replication - Process where DNA makes an exact copy of itself - Occurs during interphase - Significance: - During mitosis, the nucleus can split into 2 and each cell will have the same number of chromosomes - Each cell will be identical to each other and the parent cell ### How DNA Replication Takes Place 1. The double DNA helix unwinds 2. Weak H-bonds between nitrogenous bases break and the 2 strands of DNA unzip/separate 3. Each original DNA strand serves as a template to form a new strand 4. By attaching to free nucleotides from the nucleoplasm. 5. This forms complementary strands (A to T and C to G) 6. Each DNA molecule consists of 1 original strand and 1 new strand. 7. The result is 2 genetically identical DNA molecules. ## DNA Profiling - Each cell in a person's body has DNA and this DNA is identical in every cell of that person and it can’t be altered. - DNA profiles are a pattern of black bars left on X-ray film when an extract of DNA is put through a special process. - DNA profiling --> a method of identifying an individual by comparing his/her profile with another known DNA fingerprint. ### Uses: - Proof of paternity - Tracing missing persons - Identification of genetic disorders - Establishing family relations - Matching tissues for organ transplants - Identifying dead persons/animals ## RNA - Ribonucleic acid - 3 types: - Ribosomal RNA - Makes up the ribosomes in the cytoplasm - Catalyse the assembly of amino acids to form proteins - Messenger RNA - Found in the nucleus - Moves out of the nucleus and attaches to the ribosomes in the cytoplasm - Transfer RNA - Found in the cytoplasm ### Function - All 3 types play an important role in protein synthesis. ### Structure of RNA - Similar to DNA except: - Single-stranded - Not coiled - Sugar is ribose - Uracil instead of thymine - Short chain ### Similarities - Both contain sugar alternating with a phosphate - Both contain adenine, guanine & cytosine - Both play a role in protein synthesis ### Differences | DNA | RNA | |--------------------------------------------------------------|----------------------------------------------------------------------------------| | Found in nucleus, chloroplast & mitochondria | Found in nucleus and cytoplasm | | Long molecule | Short molecule | | Double-stranded molecule | Single-stranded molecule | | Contains sugar deoxyribose | Contains sugar ribose | | Contains nitrogenous base thymine | Contains nitrogenous base uracil | ## Protein Synthesis - Amino acids are the monomers that make up proteins. - Smallest building blocks - When amino acids combine, water is released --> dehydration synthesis - 2 AA --> dipeptide - 3/more AA --> polypeptide - 20 different amino acids - The order of the amino acids determines what protein will be formed - The sequence of nitrogenous bases in the DNA determines the sequence in which amino acids combine ### The Process of Protein Synthesis: 3 Stages: 1. Transcription 2. Movement of mRNA out of the nucleus 3. Translation ### Transcription: - The double helix DNA unwinds. - The double-stranded DNA unzips/weak hydrogen bonds break to form two separate strands. - One strand is used as a template to form mRNA using free RNA nucleotides from the nucleoplasm. - The mRNA is complementary to the DNA. - mRNA now has the coded message for protein synthesis. ### Translation: - Each tRNA carries a specific amino acid. - When the anticodon on the tRNA matches the codon on the mRNA - Then tRNA brings the required amino acid to the ribosome. - Amino acids become attached to each other by peptide bonds to form the required protein. ## The Genetic Code - The sequence of nitrogenous bases on DNA determines the sequence of bases on mRNA - The sequence of bases on mRNA determines the order in which the tRNAs are going to be attached to the mRNA - The sequence of tRNAs determine the order in which AAs are going to combine - The sequence in which AAs combine determines which protein is formed - ...DNA carries the genetic code to determine which proteins are going to be formed. | DNA | mRNA | Base triplet in DNA template | Amino acid | |---------|---------|------------------------------|----------------------------------| | GAA | CUU | GAA | Leu (leucine) | | GTA | CAU | GTA | His (histidine) | | TTT | AAA | TTT | Lys (lysine) | | GGG | CCC | GGG | Pro (proline) | | CGA | GCU | CGA | Ala (alanine) | | ACC | UGG | ACC | Trp (tryptophan) | | AAA | UUU | AAA | Phe (phenylalanine) | | CCT | GGA | CCT | Gly (glycine) |