CST Review PowerPointThe Chemistry of DNA and Molecular Genetics

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.

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.

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…

DNA vs. RNA

DNA RNA

Number of Strands

2 1

Sugar present Deoxyribose Ribose

Bases A, G, C, T A, G, C, U

Location NucleusNucleus and Cytoplasm

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?

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.

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.

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.

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.

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].

Translation

-ribosomes are involved and the site of synthesis is in the cytoplasm.

-tRNA’s carry specific amino acids to the ribosomes.

-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.

Key PlayerstRNA

The anticodon site of tRNA binds to the codons of mRNA. The

anticodon is complementary to the mRNA codons.

Ribosomes come in two sizes: a small sub-unit and a large sub-

unit.

Watch the steps at: http://www.aboutkidshealth.ca/HowTheBodyWorks/Steps-of-Translation.aspx?articleID=10190&categoryID=XG-nh4-05a

Animated movie:

Ready for the practice

questions?