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Chapter 4 Section 3

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Chapter 4 Section 3
DNA
What is DNA?
• Stands for deoxyribonucleic
acid
• Structure was first discovered
by Rosalind Franklin
• Later modeled by Watson and
Crick (they are given most credit
for discovering the structure)
Nitrogenous bases
• DNA consists of nitrogenous
bases•
•
•
•
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
A always pairs
with T
C always pairs
with G
DNA replication
•
Copy these three steps to DNA replication
RNA
• DNA cannot leave the nucleus.
• RNA is ribonucleic acid
• Molecule that leaves the nucleus to go
to the ribosomes
• Codes for making proteins
• Leaves through nuclear pores
DNA
vs
• Double stranded
• Contains A, T, G,
and C
RNA
• Single stranded
• Instead of
Thymine (T) it
has a very
similar molecule
called Urasil (U)
Therefore, in RNA, adenine pairs with Urasil
Types of RNA
• Messanger
RNA (mRNA)
• Ribosomal
RNA (rRNA)
• Transfer RNA
(tRNA)
•
Types of RNA
(continued)
• Messanger RNA
• Leaves the nucleus as a single
strand of genetic code (with Urasil
instead of Thymine)
• Ribosomal RNA
• Makes ribosomes
• Transfer RNA
• Bring amino acids to the ribosome
• Many amino acids put together make
proteins
Terms to know
• Transcription (think to “transcribe” a
letter) is copying the DNA in the
nucleus to make single stranded
RNA.
• Translation (think to “translate” a language)
is changing the mRNA to a
string of amino acids (proteins)
Mutations
• Mistakes that happen when the
DNA is being copied
• Permanent change in the DNA
sequence of a gene or
chromosome
Mutations (continued)
• Outside factors can cause:
• X Rays,
• Sunlight,
• Some chemicals
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