Nucleic acids and protein synthesis


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A Slideshow for Gr 12 Life Sciences students, focussing on aspects of nucleic acids and protein synthesis. It contains helpful information on DNA, RNA, DNA replication, transcription, translation, the importance of nucleic acids and genetic fingerprinting.

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Nucleic acids and protein synthesis

  1. 1. Module Three: Life at a Molecular, Cellular and Tissue Level Life Sciences Matric Syllabus Mind Action Series: Life Sciences Textbook and Workbook
  2. 2. • They are called ‘the molecules of life’ as they are able to store the information that controls cellular activity and the development of an organism.• They control the synthesis of proteins, which is the first step in making an entire organism.• Proteins are NB. Enzymes, which control chemical processes inside cells, are proteins. Thus, they control the structure and functions of all living organisms.• The two nucleic acids found inside cells are: – Deoxyribonucleic acid (DNA) – Ribonucleic acid (RNA) 3.1) Nucleic Acids and Protein Synthesis
  3. 3. • Located mainly in the nucleus of a cell. It forms an important part of all the chromosomes that make up the chromatin network.• The chromatin network is made up of long, thin, intertwined chromosomes. Each chromosome is made up of a thread of DNA wound around a core of proteins, known as histones.• The DNA molecule is coiled so that these long structures can fit inside the nucleus. There are nearly 2 metres of DNA in each human cell.• DNA is also found in mitochondria and in chloroplasts. 3.1) Nucleic Acids and Protein Synthesis
  4. 4. • DNA looks like a long, twisted ladder. Two strands, connected by nitrogenous bases, twist to form a stable double helix.• The DNA molecule is a long chain (polymer) made up of small units (monomers) i.e. building blocks called nucleotides. Each nucleotide is made up of the following: – A sugar molecule called deoxyribose (S) – A phosphate molecule (P) – Nitrogenous base which may be • Adenine (A) • Thyamine (T) • Guanine (G) • Cytosine (C)• These four bases are the foundation of the genetic code. They instruct cells on how to synthesise proteins and other enzymes. 3.1) Nucleic Acids and Protein Synthesis
  5. 5. • As there are four different nitrogenous bases, there are four different nucleotides.Sugar - Deoxyribose Nitrogenous base (thyamine) S T One Thyamine nucleotide P Phosphate 3.1) Nucleic Acids and Protein Synthesis
  6. 6. • The outer two strands of the ladder are formed by a chain of alternating sugar/phosphate links. The bonds between the sugar and phosphate links are strong.• The rungs are formed by pairs of bases which are linked by weak hydrogen bonds.• The base pairs are attached to the sugar molecule.• There are two groups of nitrogenous bases – purines and pyramidines. – Purines are made up of two fused rings of nitrogen, carbon and hydrogen atoms. They are larger. E.g. guanine and adenine. – Pyridmidines are made up of one fused ring of nitrogen, carbon and hydrogen atoms. They are smaller than purines. E.g. thyamine, cytosine and uracil (in RNA). 3.1) Nucleic Acids and Protein Synthesis
  7. 7. • The four base pairs have different shapes and sizes. Therefore, they link up in the following way: – Adenine will only bond with thyamine or uracil by means of two hydrogen bonds e.g. A=T, A=U – Cytosine will only bond with guanine by means of three hydrogen bonds, e.g. G≡C – A base pair will always be made up of one purine and one pyramidine. 3.1) Nucleic Acids and Protein Synthesis
  8. 8. • The four nucleotides are the same in all plants and animals. For example, an adenine nucleotide of a human is the same as the adenine nucleotide of a frog.• The difference is determined by the sequence in which the nucleotides are strung together. Different sequences have different ‘messages’, so to speak. Every human being will have a different sequence in certain sections of DNA (except for identical twins).• Thus, the SEQUENCE of nucleotides will determine the genetic code of an organism. 3.1) Nucleic Acids and Protein Synthesis
  9. 9. DNA controls all activities of the cell.•It carries coded genetic information in each cell.•It can replicate, i.e. it makes a copy of itself.•It indirectly initiates the manufacture of proteins. 3.1) Nucleic Acids and Protein Synthesis
  10. 10. • Replication is the process of using an existing DNA molecule to make an identical DNA molecule.• It takes place during the interphase (in between cell divisions) in the life cycle of a cell.• It is necessary because the DNA needs to produce another molecule, exactly the same as itself, to ensure that the genetic code is passed on to each new daughter cell formed during cell division. 3.1) Nucleic Acids and Protein Synthesis
  11. 11. • The process is catalysed by the enzyme DNA polymerase.• The double helix unwinds.• The weak hydrogen bonds holding the base pairs together break, allowing two strands to part. Each single chain of bases is exposed. 3.1) Nucleic Acids and Protein Synthesis
  12. 12. • Free nucleotides in the cytoplasm become attached to their matching, exposed base partners. 3.1) Nucleic Acids and Protein Synthesis
  13. 13. • The fact that only A will bond with T and C only with G, ensures that the sequence in the daughter cell will be EXACTLY the same as in the parent DNA. 3.1) Nucleic Acids and Protein Synthesis
  14. 14. • RNA is made in the nucleus by DNA. It is involved in protein synthesis.• The RNA is structured as such: – Like DNA, it is a polymer made up of nucleotides. – Unlike DNA, it consists of a single strand. – It is shorter than DNA. – The sugar is ribose, not deoxyribose.• The function of RNA is to carry instructions from DNA in the nucleus to the ribosomes in the cytoplasm of a cell where it controls the synthesis of proteins from amino acids. 3.1) Nucleic Acids and Protein Synthesis
  15. 15. RNA DNASingle - stranded 2 strandsMuch shorter than DNA Long moleculeNot double helix Double HelixContains uracil Contains ThyamineContains ribose Contains deoxyriboseFunction: Transcription Functions: Contains genetic information Replication 3.1) Nucleic Acids and Protein Synthesis
  16. 16. • Proteins are responsible for a number of reactions which occur around the body: they are enzymes, hormones, antibodies, collagen, haemoglobin, fibrin, actin and myosin, as well as hoof, nails and hair.• Proteins are created via protein synthesis, a process which will be explained in two main stages: 1) Transcription and 2) Translation. Translation is the actual process of protein synthesis. transcription translation DN mR p ro te i in nucleus in ribosomes A NA n 3.1) Nucleic Acids and Protein Synthesis
  17. 17. • There are three different types of RNA: – Messenger RNA (mRNA) – Transfer RNA (tRNA) – Ribosomal RNA (rRNA) 3.1) Nucleic Acids and Protein Synthesis
  18. 18. • mRNA is formed in the nucleus, in a similar way to the replication of DNA. The coded message in DNA is carried across – transcribed – into the new mRNA molecule, which carries it to the ribosomes.• Transcription takes place in the following way: – A small piece of DNA, a gene, unwinds and the two strands separate. – New nucleotides pair up with the complementary bases on one of the DNA strands. This strand is the template as it carries the code. – The nucleotides join and form a strand of mRNA. – A completed strand of mRNA breaks away from the DNA. The DNA then rezips. – mRNA moves through the pores of the nuclear membrane and carries the genetic code to the ribosomes which are the sites of protein synthesis. 3.1) Nucleic Acids and Protein Synthesis
  19. 19. • The mRNA, with its codons, moves through the pores of the nuclear membrane into the cytoplasm where it binds with a ribosome.• The tRNA with it’s anti-codons links up with a specific amino acid in the cytoplasm.• tRNA brings its amino acid to the ribosome where the anti-codon links up with the complimentary codon.• The amino acid is released an links up with the adjacent amino acid by means of a peptide bond. The tRNA molecule is also released. The rRNA moves along the mRNA stand, reading the code.• When the end is reached, a completed polypeptide chain is formed, built according to the code which was originally copied from the DNA code in the nucleus. 3.1) Nucleic Acids and Protein Synthesis
  20. 20. • Just as each person’s fingerprint is unique, the DNA coding for every individual is unique – except for identical twins.• Most of the 3 billion nucleotides we inherit, are identical among all humans.• Certain parts of the non-coding DNA vary among individuals. These parts differ due to changes taking place in the structure or position of the nucleotides (gene mutations) and they are used in making a genetic fingerprint.• Each of our cells carries an identical set of unique DNA. If two genetic fingerprints show identical banding patterns, it is virtually certain that they come from the same person.• Relatives will have some consistency in certain parts of their DNA. 3.1) Nucleic Acids and Protein Synthesis
  21. 21. Genetic fingerprinting can be used to:•Solve crimes•Diagnose inherited disorders in unborn and newborn babies•Establish paternity•Identify casualties 3.1) Nucleic Acids and Protein Synthesis