CH. 12.3 : DNA, RNA, and Protein

1
CH. 12.3 DNA, RNA, and Protein

• Section Objectives
• Relate the concept of the gene to the sequence
  of nucleotides in DNA.
• Sequence the steps involved in protein synthesis.
• Explain the different types of RNA involved in
  protein synthesis

2
Genes and Proteins

• The sequence of nucleotides in DNA contain
  information.
• This information is put to work through the
  production of proteins.
• Proteins fold into complex, three-
  dimensional shapes to become key cell
  structures and regulators of cell functions.
• Thus, by encoding the instructions for making
  proteins, DNA controls cells.

3
Genes and Proteins

• You learned earlier that proteins are polymers
  of amino acids.
• The sequence of nucleotides in each gene
  contains information for assembling the string
  of amino acids that make up a single protein.

4
DNA ? Proteins ? Cells ? Bodies

• DNA has the information to build proteins
• genes

proteins
cells
DNA gets all the glory,Proteins do all the work
bodies
5
Cell organization

• DNA
• DNA is in the nucleus
• genes instructions for making proteins
• want to keep it there protected
• locked in the vault

cytoplasm
nucleus
6
Cell organization

• Proteins
• chains of amino acids
• made by a protein factory in cytoplasm
• protein factory ribosome

cytoplasm
buildproteins
ribosome
7
Passing on DNA information need RNA

• RNA like DNA, is a nucleic acid
• RNA structure differs from DNA structure in three
  ways.
• 1. Has ribose sugar instead of deoxyribose (DNA)
• 2. Replaces thymine (T) with uracil (U)
• 3. Single stranded as opposed to double stranded
  DNA

Nitrogenous base(A, G, C, or U)
Phosphategroup
Uracil (U)
Sugar(ribose)
8
RNA

• RNA has a different function than DNA
• Whereas DNA provides the instructions for protein
  synthesis, RNA does the actual work of protein
  synthesis.
• RNAs take from DNA the instructions on how the
  protein should be assembled, thenamino acid by
  amino acidRNAs assemble the protein.

9
RNA

• 3 types of RNA
• 1. Messenger RNA (mRNA), single, uncoiled strand
  which brings instructions from DNA in the nucleus
  to the site of protein synthesis.
• 2. Ribosomal RNA (rRNA), globular form, makes up
  the ribosome the construction site of proteins
  binds (site of protein synthesis) binds to the
  mRNA and uses the instructions to assemble the
  amino acids in the correct order.
• 3. Transfer RNA (tRNA) single, folded strand that
  delivers the proper amino acid to the site at the
  right time

10
Passing on DNA information

• Need to get DNA gene information from nucleus to
  cytoplasm
• need a copy of DNA
• messenger RNA

cytoplasm
buildproteins
mRNA
ribosome
11
Protein Synthesis 2 step process1.
Transcription 2. translation

• 1.Transcription DNA -gt mRNA
• In the nucleus, enzymes make an RNA copy of a
  portion of a DNA strand
• The main difference between transcription and
  DNA replication is that transcription results in
  the formation of one single-stranded RNA molecule
  rather than a double-stranded DNA molecule.
• 2. Translation mRNA -gt Protein
• process of converting the information in a
  sequence of nitrogenous bases in mRNA into a
  sequence of amino acids in protein

12
From nucleus to cytoplasm
transcription
protein
mRNA
DNA
translation
trait
nucleus
cytoplasm
13
Transcription

• Making mRNA from DNA
• DNA strand is the template (pattern)
• match bases
• U A
• G C
• Enzyme
• RNA polymerase

14
Matching bases of DNA RNA

• Double stranded DNA unzips

A
G
G
G
G
G
G
T
T
A
C
A
C
T
T
T
T
T
C
C
C
C
A
A
15
Matching bases of DNA RNA

• Double stranded DNA unzips

A
G
G
G
G
G
G
T
T
A
C
A
C
T
T
T
T
T
C
C
C
C
A
A
16
Matching bases of DNA RNA
A

• Match RNA bases to DNA bases on one of the DNA
  strands

C
U
G
A
G
G
U
C
U
U
G
C
A
C
A
U
A
G
A
C
U
A
G
A
C
C
A
G
G
G
G
G
G
T
T
A
C
A
C
T
T
T
T
T
C
C
C
C
A
A
17
Matching bases of DNA RNA

• U instead of T is matched to A

TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCC
mRNA
18
RNA Processing

• Not all the nucleotides in the DNA of eukaryotic
  cells carry instructionsor codefor making
  proteins.
• Genes usually contain many long noncoding
  nucleotide sequences, called introns, that are
  scattered among the coding sequences.
• Regions that contain information are called exons
  because they are expressed.
• When mRNA is transcribed from DNA, both introns
  and exons are copied.
• The introns must be removed from the mRNA before
  it can function to make a protein.
• Enzymes in the nucleus cut out the intron
  segments and paste the mRNA back together.
• The mRNA then leaves the nucleus and travels to
  the ribosome.

19
RNA Processingsimplified

• Noncoding segments called introns are spliced out
  ( coding segment exons)

20
Genetic information written in codons is
translated into amino acid sequences

• Transfer of DNA to mRNA uses language of
  nucleotides
• Letters nitrogen bases of nucleotides
  (A,T,G,C)
• Words codons triplets of bases
• ( ex. AGC)
• Sentences polypeptide chain
• The codons in a gene specify the amino acid
  sequence of a polypeptide

21
The Genetic Code

• The nucleotide sequence transcribed from DNA to a
  strand of messenger RNA acts as a genetic
  message, the complete information for the
  building of a protein..
• Virtually all organisms share the same genetic
  code

22
Translation From mRNA to Protein

• takes place at the ribosomes in the cytoplasm.
• Involves 3 types of RNA
• 1. Messenger RNA (mRNA) carries
• the blueprint for construction of a protein
• 2. Ribosomal RNA (rRNA)
• the construction site where the protein is
  made
• 3. Transfer RNA (tRNA)
• the truck delivering the proper amino acid
  to the site at the right time

23
Transfer RNA molecules serve as interpreters
during translation

• In the cytoplasm, a ribosome attaches to the mRNA
  and translates its message into a polypeptide
• The process is aided by transfer RNAs
• Each tRNA molecule has a triplet anticodon on one
  end and an amino acid attachment site on the
  other
• Anticodon base pairs with codon of mRNA

24
cytoplasm
protein
nucleus
trait
25
How does mRNA code for proteins

• mRNA leaves nucleus
• mRNA goes to ribosomes in cytoplasm
• Proteins built from instructions on mRNA

How?
26
How does mRNA code for proteins?

• How can you code for 20 amino acids withonly 4
  DNA bases (A,U,G,C)?

27
mRNA codes for proteins in triplets

• Codon block of 3 mRNA bases

28
The Genetic code

• For ALL life!
• strongest support for a common origin for all
  life
• Code has duplicates
• several codons for each amino acid
• mutation insurance!

• Start codon
• AUG
• methionine
• Stop codons
• UGA, UAA, UAG

29
How are the codons matched to amino acids?
TACGCACATTTACGTACGCGG
DNA
AUGCGUGUAAAUGCAUGCGCC
mRNA
codon
anti-codon
aminoacid

• Anti-codon block of 3 tRNA bases

30
mRNA to protein Translation

• The working instructions ? mRNA
• The reader ? ribosome
• The transporter ? transfer RNA (tRNA)

C
31
From gene to protein
transcription
translation
protein
mRNA
DNA
trait
nucleus
cytoplasm
32
cytoplasm
protein
transcription
translation
nucleus
trait
33
From gene to protein
protein
transcription
translation