Chapter 7 The Blueprint of life, from DNA to Protein Flashcards
Genetics
The science of heredity
Molecular Biology
- The science dealing with DNA and protein synthesis
- Total DNA contained in the cell - Genome (Consists of the chromosomes and any plasmids)
DNA
Macromolecule made of genes
Each nucleotide in DNA has:
1) Nitrogenous Base (A, T, G, C)
- A with T (2 hydrogen bonds)
- G with C (3 hydrogen bonds)
2) Sugar (deoxyribose) – Numbered 1’ to 5’
3) A phosphate
Double Helix (DNA)
- Two strands are held together by hydrogen bonds between bases
- Strands of DNA are complementary (Sequence of one strand determines sequence of other)
- Nucleotides are linked by covalent phosphodiester bonds
- 5’ Carbon joins to 3’ with a phosphate between
- DNA is read from 5’ to 3’ direction
- Two strands of DNA run antiparallel
The Flow of Genetic Information
1) DNA is copied before the cell division - Replication
2) DNA is used to make proteins - Gene Expression
3) DNA can flow between 2 different bacterial cells - Recombination
DNA Replication
- One parental double stranded DNA molecule is used to make 2 identical double stranded DNA molecules
- Because the stands are complementary:
One strand can serve as a template for synthesis of the other strand
DNA polymerase reads the order of nucleotides in the template strand to make a complementary new strand
First Step of DNA Replication
A small segment of the DNA un-winds and the strands are separated
- Forms the replication fork
- Each separated strand serves as template for synthesis of a complementary strand
- A short RNA primer is produced by the enzyme: Primase
- Serves as starting site for nucleotides to form new strand of DNA
Second Step of DNA replication
Synthesis of the Leading Strand
- DNA pol can only synthesize DNA in one direction = 5’ - 3’
- Template must be read in the 3’ to 5’ direction
- Follows the replication fork
- Synthesis of the leading strand is continuous in the 5’ to 3’ direction
Third Step of DNA Replication
Synthesis of the Lagging Strand
-DNA polymerase can only make DNA in 5’ to 3’ direction
- But the second strand must be made in the opposite direction
- DNA polymerase synthesizes small fragments of DNA: Okazaki Fragments
Made in the 5’ to 3’ direction
Afterwards, the RNA primers are removed and the fragments are joined together by enzyme DNA ligase
Gene Expression
1) Transcription - Information stored in DNA is copied into RNA
2) Translation - Information in RNA is decoded to make protein
Transcription
- Synthesis of RNA from a DNA template
- Sequence is complementary to a gene – Except it contains U instead of T
Three Types of RNA
1) Messenger RNA (mRNA) - Carries information for making specific protein
2) Ribosomal RNA (rRNA) - forms part of the ribosome
3) Transfer RNA (tRNA) - transports specific amino acids for protein synthesis
Initiation (1 Transcription)
- RNA polymerase binds to the gene at specific site called the promoter
- Separates (melts) the two strands
- Only one DNA strand is copied - the template
- The template is read in the 3’ - 5’ direction so that RNA can be made in the 5’ - 3’ direction
Elongation (2 Transcription)
- RNA polymerase moves along the templates synthesizing new RNA
- Allows the DNA to rewind behind it
