Transcript Transcription

BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 10
Molecular Biology of the Gene
Modules 10.6 – 10.16
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
THE FLOW OF GENETIC INFORMATION
FROM DNA TO RNA TO PROTEIN
• DNA is our genetic material: it contains the information
coded by our genotypes
• RNA contains the instructions for making proteins
• Proteins are necessary for all life functions
• DNA  RNA  Protein is the central dogma of molecular
biology
• Transcription is the process of making RNA from DNA
• Translation is the process of making proteins from RNA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• DNA is transcribed (goes through
transcription) to become RNA which is then
translated (goes through translation) to
become protein.
DNA
TRANSCRIPTION
RNA
TRANSLATION
Protein
Figure 10.6A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
10.7 Codons
• A codon is a 3 nucleotide sequence that specifies a
specific amino acid (building block of protein).
• For example, in DNA you might have: ACG
• After transcription, the RNA codon would be: UGC
• After translation, the amino acid that matches that
codon is cysteine.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
10.8 The genetic code
• There are 64 possible
triplet combinations
that match up with
specific amino acids
(there are 20 different
amino acids)
• AUG codes for the start
of a polypeptide chain
• UAA, UAG, and UGA
code for stop
Figure 10.8A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Bacteria, plants and animals all have DNA and
go through the same process to make protein
Transcribed strand
DNA
Transcription
RNA
Start
codon
Polypeptide
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Translation
Stop
codon
Figure 10.8B
• Transcription occurs in the nucleus
• 1. DNA unzips
• 2. RNA nucleotides match up in triplets called mRNA
(messenger RNA) *remember, C with G and A with U (not
T)*
• 3. RNA polymerase links up these nucleotides
• 4. A promoter tells the RNA polymerase where to copy the
nucleotides, and a terminator tells it when to stop
• 5. The new RNA strand elongates and then peels away from
the DNA
Figure 10.9B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
10.10 Eukaryotic RNA is processed before leaving
the nucleus
• Before the mRNA leaves
the nucleus, a cap (made
of one G) and a tail (made
of lots of As) is added.
• Introns (non-coding
regions) are removed and
exons (coding regions)
are joined.
• This process is called
RNA splicing.
• mRNA now goes into the
cytoplasm
Figure 10.10
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Exon Intron
Exon
Intron
Exon
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
NUCLEUS
CYTOPLASM
10.11 Translation
• Translation (RNA to protein) occurs in the cytoplasm and in
ribosomes
• Transfer RNA (tRNA) matches up the mRNA codons with
amino acids
• 1. Each mRNA codon matches up with one end of a tRNA
(called the anti-codon).
• 2. The other end of the tRNA then attaches to the amino acid
that the anti-codon tells it to.
• 3. The tRNA then line up the amino acids in order to form a
protein. *this occurs in a RIBOSOME*
Figure 10.11A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• tRNA
Amino acid
attachment
site
Anticodon
Figure 10.11B, C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Proteins are assembled in ribosomes.
• Ribosomes are made of 2 subunits.
• They are made of rRNA (ribosomal RNA, the most
abundant kind of RNA)
Large
ribosomal
subunit
Initiator tRNA
P site
A site
Start
codon
mRNA
Small ribosomal
subunit
1
Figure 10.13B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
2
10.16 Mutations can change the meaning of genes
• Mutations are changes in the DNA base sequence
– These are caused by errors in DNA replication or by
mutagens (a physical or chemical agent such as UV
light, x-rays, chemicals)
– Mutagenesis is the creation of mutations
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings