DNAStructure, replication, transcription

DNA is composed of nucleotides- which contain a phosphate group, a sugar (deoxyribose), and a nitrogen containing base

Structure of DNA

There are four Nitrogen-containing bases of DNA: adenine, guanine (purines- double ring) and thymine, cytosine (pyrimidines- single ring)

Structure of DNA

When bases pair up to form a DNA molecule, thymine always pairs with adenine, and guanine always pairs with cytosine

A-T G-C The base pairs areheld together by hydrogen bonds

Structure of DNA

1. A DNA molecule unzips (helicase enzyme) as nucleotide base pairs separate. Replication begins on both strands of the molecule at the same time

2. Each existing strand of the DNA molecule is a template for a new strand. Free floating nucleotides pair up with the exposed bases on each template strand. DNA polymerases bond these nucleotides together to form the new strands.

3. Two identical DNA molecules result from replication.

DNA replication

DNA Replication

1. A large transcription complex made of RNA polymerase and other proteins recognizes the start of a gene and begins to unwind the segment of DNA.

2. RNA polymerase uses one strand of the DNA as a template. RNA nucleotides form complementary base pairs with the DNA template. A-U (uracil) and G-C

The growing RNA strand hangs freely as it is transcribed. Then the DNA strand closes back together.

3. The completed RNA strand separates from the DNA template and the transcription complex falls apart.

Transcription- DNA to RNA

http://sepuplhs.org/high/sgi/teachers/genetics_act16_sim.html

Transcription produces three major types of RNA molecules

1. messenger RNA - intermediate message that is translated to form proteins

2. ribosomal RNA -forms part of ribosomes 3. transfer RNA –brings amino acids from

the cytoplasm to the ribosome

Transcription