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The Chemistry of DNA and Molecular Genetics

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1 The Chemistry of DNA and Molecular Genetics
CST Review PowerPoint The Chemistry of DNA and Molecular Genetics

2 Introducing…DNA -DNA is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. -The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

3 Important! The DNA molecule has two important properties:
It can make copies of itself. If you pull the two strands apart, each can be used to make the other one (and a new DNA molecule). It can carry information. The order of the bases along a strand is a code - a code for making proteins.

4 Strands go 5’ to 3’ one way and 3’ to 5’ the other way…
Structure of DNA -Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by bonds. -These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. Strands go 5’ to 3’ one way and 3’ to 5’ the other way…

5 DNA vs. RNA DNA RNA Number of Strands 2 1 Sugar present Deoxyribose
Bases A, G, C, T A, G, C, U Location Nucleus Nucleus and Cytoplasm

6 DNA and Chromosomes -DNA molecules are tightly packed around proteins called histones to make structures called chromosomes. Q: Do you remember how many chromosomes are present in a human diploid cell (somatic cells)? Gametes? What is significant about this tight packaging?

7 DNA Replication -Every time a cell divides, DNA must be able to make a copy of itself. -To make a copy of itself, the twisted, compacted double helix of DNA has to unwind and separate its two strands. Each strand becomes a pattern, or template, for making a new strand, so the two new DNA molecules have one new strand and one old strand. -A host of enzymes, DNA polymerase, helicase, ligases, play a part in the complicated steps involved in DNA synthesis.

8 Salient points… -Complementary Base Pairing- A bonds with T & C bonds with G. -DNA polymerase can only act in the 5’ to 3’ direction (so nucleotide synthesis proceeds at two different direction at the replication fork). -A replication fork forms at the site where DNA synthesis is occurring at the exposed parent strands.

9 Continuous and Discontinuous Synthesis
The direction of replication is 5’  3’. Replication is continuous when at the 3’-5’ parent strand and discontinuous at the 5’-3’ parent strand. Okazaki fragments form where synthesis is discontinuous.

10 Central Dogma The central dogma of molecular biology explains how information flows from DNA to RNA to proteins. Protein synthesis involve two stages: Transcription and Translation.

11 Transcription -is RNA synthesis.
-mRNA is created inside the nucleus using a parent DNA template. -RNA polymerase is involved. -Before the mRNA transcript leaves the nucleus, it is processed. -Question: Quiz: Transcribe RNA from a strand of DNA “A G C T G T A C A.” [Remember: there is no Thymine in RNA].

12 Translation -is the actual manufacture of proteins using mRNA.
-each ‘trio’ of bases on RNA serves as a code (codon) for an amino acid. This code is universal. -ribosomes are involved and the site of synthesis is in the cytoplasm. -tRNA’s carry specific amino acids to the ribosomes.

13 Ribosomes come in two sizes: a small sub-unit and a large sub-unit.
Key Players tRNA Ribosomes come in two sizes: a small sub-unit and a large sub-unit. The anticodon site of tRNA binds to the codons of mRNA. The anticodon is complementary to the mRNA codons.

14 Ready for the practice questions?
Animated movie: Watch the steps at: Ready for the practice questions?

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