Transcript Structure & Function of DNA

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1. How is all life connected?
2. What creates diversity?
Structure & Function of DNA
History
Structure of DNA
Polymer: Nucleic Acid
Monomer: Nucleotides(has three sub units)
1. Deoxyribose (sugar)
2. Phosphate
3. Nitrogen Base: four kinds
• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)
Structure of DNA
• Phosphates of one
nucleotide binds to
the sugar of another
to make the sugarphosphate backbone
DNA has 2 backbones and the bases pair up to connect
the two backbones together
** This results in the “Double Helix” structure of DNA**
Complimentary Base Pairing
Base pairing:
• A-T, T-A
• C-G, G-C.
All Living things have DNA with this basic
structure with these nucleotides and the 4
nitrogen bases.
Variation among all living things is due to the
different sequences and lengths of ATCG
in their DNA
DNA Function
Used to make more DNA or all proteins in
cell. Three processes involving DNA;
Replication, transcription, and translation
1) Replication: DNA  DNA
- Happens in S phase of Cell Cycle.
Resulting in sister chromatids.
DNA Function: Protein
synthesis
1. Transcription: DNA  RNA; Takes
place in the nucleus
• DNA cannot leave the nucleus (double
stranded = too big)
• Where is protein made; what organelle?
• Need to get the code in the DNA to the
ribososmes in the cytoplasm so they
make the right protein.
• RNA is also a nucleic acid, but different
from DNA
Differences between DNA &
RNA
• Single Stranded (can leave the nucleus)
• Different sugar in nucleotide (Ribose)
• Has Uracil (U) instead of (T)
A-U,U-A
Steps to Transcription
1) Unzipping of the DNA
2) Complimentary base paring new
Ribonucleotides to the DNA bases
Three Kinds of RNA
• mRNA= messenger RNA (has codons)
• tRNA= transfer RNA (has anticodons and amino
acids)
• rRNA= ribosomal RNA
These 3 types of RNA are needed to perform
translation.
2. Translation: RNA  Protein
When protein is made in ribosomes (the
cytoplasm or on E.R.)
All proteins are made from only 20 amino
acids
A code from the base combinations on the
mRNA makes the 20 Amino Acids=Codon
Codons are universal; all organisms share
the same code for the same 20 amino
acids. (pg 303)
Start codon
Translation
Process
1) mRNA leaves the nucleus and attaches to
a ribosome
2)tRNA carries a specific amino acid to the
ribosome and base pairs its anti-codon to
the mRNA’s codon
3)The ribosome can fit three tRNA
molecules, and their specific amino acids
form peptide bonds between each other.
Phenylalanine
tRNA
Methionine
Ribosome
mRNA
Start codon
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Lysine
Translation
Process (Cont’d)
4) The ribosome moves down the mRNA
molecule leaving behind a chain of amino
acids linked together (a protein).
Lysine
tRNA
Translation direction
mRNA
Ribosome
Copyright Pearson Prentice Hall
Polypeptide
Ribosome
tRNA
mRNA
Copyright Pearson Prentice Hall
Application Problems
Steps:
1) ID coding strand of DNA
2) Make complimentary strand (or visa
versa)
3) Transcribe: Make the mRNA, find start
and stop codons
4) Translate: Base pair the tRNA to mRNA
5) Translate: Write down the amino acids
associated to each tRNA molecule.