CST Review PowerPoint

1
CST Review PowerPoint

• The Chemistry of DNA and Molecular Genetics

2
IntroducingDNA

• -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
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 Ribose
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?

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.
• -tRNAs carry specific amino acids to the
  ribosomes.

13
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
Animated movie

• Watch the steps at http//www.aboutkidshealth.ca/
  HowTheBodyWorks/Steps-of-Translation.aspx?articleI
  D10190categoryIDXG-nh4-05a

Ready for the practice questions?