Nucleic Acids and Protein Synthesis

1. Nucleic Acids and Protein Synthesis Chapter 10

2. DNA or Deoxyribonucleic acid job is to store and transmit the genetic information that tells cells which proteins to make and when to make them • Proteins in turn form the structural units of cells and help control chemical processes within the cell. • DNA is the most important part of our body, it controls everything. DNA

3. DNA is made up of nucleotides. A nucleotide has three parts • 1) A sugar called deoxyribose • 2) A phosphate group • 3) a nitrogen containing base • There are 4 nitrogen containing bases • Adenine - A • Thymine - T • Cytosine - C • Guanine - G Structure of DNA

4. The nucleotides have different structures • Purines – like adenine and guanine have 2 rings of carbon and nitrogen atoms. • Pyrimidines- like cytosine and thymine have one ring of Carbon and Nitrogen atoms. Structure of DNA cont.

6. DNA is composed of two nucleotide chains that wrap around each other to form a double spiral. This spiral is called a Double Helix • The double helix was discovered by James Watson and Francis Crick in 1953. • They used a photograph taken by Rosalind Franklin. • The sides of the helix are an alternating sugar phosphate backbone and the rungs of the helix are the nitrogen containing bases. The Double Helix

8. The nitrogen bases pair up. • Adenine bonds to Thymine (A-T) • Cytosine bonds to Guanine (C-G) • These are called complementary base pairs. • The rules are called base-pairing rules • The base pairs are connected by hydrogen bonds. • These base pairs allow DNA to easily copy itself. Complementary Base Pairing

9. The copying of DNA is called Replication. • The first step is to separate the two chains of DNA. • This is done at the replication fork. • The chains are separated by enzymes called helicases. • The helicases break the hydrogen bonds. • Then enzymes called DNA polymerase move along the chains and new chains are created. Replication of DNA

10. It is easy for DNA to copy itself because of its base pair rule. • A ALWAYS BINDS to T • C ALWAYS BINDS to G • A complementary strand of DNA is created to each other half. DNA Replication cont.

11. There is about one error for every 10,000 paired nucleotides. • A change in DNA is called a mutation . • A mutation can have serious side effect to the human body. • The base pair rule makes it hard for errors to occur. • DNA also proofreads itself to prevent mutations. • Mutations can occur randomly or can be influenced by the environment. Accuracy and Repair

12. The nucleic acid called RNA or Ribonucleic acid is responsible for the movement of genetic information from the DNA in the nucleus to the site of protein synthesis in the cytosol. • RNA is responsible for making proteins that our body needs to live. RNA : Section 2

13. RNA is also made up of nucleotides but differs in structure from DNA • The sugar molecule in every molecule of RNA is ribose • Thymine Is rarely found in RNA instead the nitrogen base that is used is uracil. • Therefore A binds with U and C binds with G • A-U • C-G Structure of RNA

14. Messenger RNA (mRNA) consists of RNA nucleotides in the form of a single uncoiled chain. mRNA carries the genetic information from the DNA in the Nucleus to the cytosol. • Transfer RNA (tRNA) consists of a single chain of about 80 nucleotides folded into a hairpin shape that binds to specific amino acids. • Ribosomal RNA (rRNA) is the most abundant RNA and consists of nucleotides in a globular form. rRNA makes up the ribosomes where proteins are made. Types of RNA

15. The process by which genetic information is copied from DNA to RNA is called Transcription. • RNA polymerase synthesizes RNA copies of a specific sequence of DNA. It does this by binding to specific regions of DNA called Promoters. • The promoter marks the beginning of the DNA strand to be transcribed. • This then separates the DNA chain. Transcription

16. Only one of the separated DNA chains is used for transcription, this is called the template. • The base pair rule is then used and a strand of RNA is formed. • Remember A-U and C-G • Transcription then continues until it reaches the termination signal. • All three types of RNA are formed this way. Transcription cont.

17. The products are called transcripts. • And they are the three types of RNA • mRNA, tRNA and rRNA • All three are used in the synthesis of proteins. • After Transcription mRNA moves through pores of the nuclear membrane into the cytosol where it directs the synthesis of proteins. Products of Transcription

18. The production of proteins is also called protein synthesis. • The amount and kind of proteins that are produced in a cell determine the structure and function of the cell. • Proteins carry out the genetic instructions encoded in an organisms DNA Protein Synthesis: Section 3

19. Proteins are polymers and they are made up of polypeptides. • Each polypeptide consists of amino acids linked together by peptide bonds. • There are 20 different amino acids and a protein can be made up of thousands of amino acids. • The sequence of amino acids determine the structure of the protein. • The function depends on the proteins ability to bind with other molecules in the cell. Protein structure

20. A correlation between a nucleotide sequence and an amino acid sequence is called the genetic code, this code is used by most organisms to translate mRNA transcripts into proteins. • The combination of three mRNA nucleotides is called a codon. • Each codon codes for a specific amino acid. • There are 64 codons. The genetic code

21. Several codons code for each amino acid. • Codons are different by the third nucleotide. • The start codon AUG engages ribosomes to start translating mRNA • The stop codons UAA, UAG, UGA cause ribosomes to stop translating mRNA The genetic code cont.

22. The process of assembling polypeptides from information encoded in mRNA is called translation. • This begins when mRNA leaves the nucleus. • The mRNA then finds a ribosome in the cytosol, which is the site of protein synthesis. Translation

23. Amino acids floating freely in the cytosol are transported to the ribosomes by tRNA • tRNA has a region that bonds to a specific amino acid. • The loop opposite the site of amino acid attachment has a sequence of three nucleotides called and anticodon. • The anticodon is complementary to and pairs with its complementary mRNA codon tRNA and Anticodons

24. Ribosomes are composed of rRNA and proteins are usually both free in the cytosol and attached to the endoplasmic reticulum. • Proteins used with in the cell are made on the unattached ribosomes. • Proteins to be used outside the cell are made on the attached ribosomes. Ribosomes

25. The assembly of a polypeptide begins when a ribosome attaches to the start codon of an mRNA transcript. Protein Assembly