Molecular Biology Chapter 17 Outline

Front 1

Gene Expression

Back 1

Process by which information encoded in DNA directs the synthesis of proteins.

Front 2

Archibald Garrod (1902)

Back 2

genes dictate phenotypes through enzymes that catalyze specific chemical reactions; inherited diseases result from a person’s inability to make a specific enzyme. Example: alkaptonuria

Front 3

Beadle & Tatum (1920’s)

Back 3

through a series of experiments determined that for every enzyme, a specific gene exists (one gene – one enzyme hypothesis). Example: bread mold

Front 4

Transcription

Back 4

Synthesis of RNA using a DNA template (DNA making copies of RNA).

Front 5

mRNA (messenger)

Back 5

Attaches to ribosomes in the cytoplasm and specifies the primary structure of protein (enzyme).

Front 6

DNA RNA subunits: Nucleotides

Back 6

Sugar (deoxyribose or ribose)
Phosphate
Nitrogenous base (A,C, G, T, or U)

Front 7

Nitrogenous bases

Back 7

Pyrimidines (C, T, or U)
Purines (A, G)
i

Front 8

Complementary base-pairing

Back 8

A-T (DNA) or A-U (RNA)
C-G (DNA and RNA)

Front 9

Translation

Back 9

Synthesis of a protein using genetic information encoded in a mRNA molecule (translating nucleic acids into amino acids).

Front 10

Ribosome

Back 10

Site of protein synthesis; complex of rRNA and protein molecules.

Front 11

Transcription occurs in the

Back 11

nucleus, and mRNA is transported to the cytoplasm where translation occurs.

Front 12

The Genetic Code

Back 12

Four nucleotide bases code for 20 amino acids.
Each amino acid is represented by a combination of three nucleotide bases.

Front 13

Triplet code

Back 13

Genetic information system in which a set of 3-nucleotide base sequences specify the amino acids for proteins. 1 codon = 1 Amino Acid
a) DNA → RNA → Protein

Front 14

Template strand

Back 14

DNA strand that provides a pattern or blueprint for building the complementary sequence of nucleotides in an RNA transcript.

Front 15

An mRNA molecule is complementary to its DNA template because RNA bases are assembled to the same base-pairing rules used in DNA replication.

Back 15

a) DNA: A – T and C – G
b) RNA: A – U and C – G

Front 16

Codon

Back 16

Three nucleotide sequence of DNA or mRNA that specifies a specific protein or
termination signal; basic unit of the genetic code. Start & Stop codon are not Amino Acids.

Front 17

Marshall Nirenberg (1961)

Back 17

deciphered the first genetic code (UUU → phenylalanine). All 64 genetic codes were deciphered by the mid-1960’s
61 of the 64 codons code for amino acids (the other three codons are stop codons).
A single amino acid may have more than one codon, but those codons code for no other amino acids

Front 18

Molecular Components

Back 18

RNA polymerase
Promoter
Terminator
Transcription unit

Front 19

RNA polymerase

Back 19

Enzyme that links ribonucleotides into an elongating RNA chain during RNA transcription; complementary base-pairing on a DNA template .Hit it & quit it.

Front 20

Promoter

Back 20

DNA sequence where RNA polymerase attaches and initiates transcription.

Front 21

Terminator

Back 21

DNA sequence that signals an end to transcription.

Front 22

Transcription unit

Back 22

Stretch of DNA that is transcribed into an RNA molecule.

Front 23

Synthesis of RNA Transcript

Back 23

Stage 1: Initiation
Stage 2: Elongation
Stage 3: Termination

Front 24

Stage 1: Initiation

Back 24

After RNA polymerase binds to the promoter, the DNA strands unwind and the polymerase initiates RNA synthesis at the start point.

Front 25

transcription factor

Back 25

Regulatory protein that binds to DNA and affects the transcription of specific genes (TF).

Front 26

transcription initiation complex

Back 26

Completed assembly of TF and RNA polymerase bound to the promoter.

Front 27

Stage 2: Elongation

Back 27

A. RNA polymerase moves downstream, un-winding DNA, elongating the RNA transcript (5’–3’); in the wake of transcription, the DNA strands reform the double helix.
B. Progresses at a rate of approximately 40 nucleotides/second.
C. Can be accomplished with multiple RNA polymerases working simultaneously.

Front 28

Stage 3: Termination

Back 28

a) Eventually, the RNA transcript is released and RNA polymerase detaches from the DNA.
b) 10 – 35 nucleotides downstream from the terminator signal, proteins cut the RNA transcript
(pre-mRNA) free from RNA polymerase. Like a buffer

Front 29

Alteration of mRNA Ends- RNA processing

Back 29

Modification of RNA primary transcripts.
a) 5’ cap: Modified guanine (G) nucleotide.
b) poly-A tail: Addition of adenine (A) nucleotide.
c) purpose
i. Facilitate the export of mRNA from the nucleus.
ii. Protect mRNA from enzymatic degradation.
iii. Facilitate ribosomal attachment to mRNA.

Front 30

RNA splicing

Back 30

Removal of portions of the RNA transcript (introns) that will not be included in the mRNA; and the joining together of the remaining portions (exons).

Front 31

intron (intervening sequences)

Back 31

Noncoding segments of nucleic acids that lie between coding segments; segments that will be removed.(in between; GO OUT)

Front 32

exon (expressed sequences)

Back 32

Coding segments of nucleic acids that will eventually be expressed as amino acids; segments that remain. Stay in; EXPRESSED

Front 33

snRNP’s (small nuclear ribonucleoproteins)

Back 33

RNA and protein molecules capable of recognizing
short nucleotide sequences at the end of each intron.

Front 34

Spliceosome

Back 34

Large complex composed of proteins + snRNPs that interacts with an intron, releasing the intron, and joining the two adjacent exons.

Front 35

Ribozymes

Back 35

RNA molecule that functions as an enzyme – an intron that catalyzes its own removal during RNA splicing.
i. Ribozymes can possess a specific 3D shape.
ii. Some bases can participate in catalysis.
iii. H-bonding adds specificity to catalytic activity.

Front 36

Molecular Components

Back 36

1. tRNA (transfer)
2. Codon
3. Anticodon
4. Aminoacyl-tRNA synthetase
5. Wobble
6. Ribosomes

Front 37

tRNA (transfer)

Back 37

Functions as a translator between nucleic acid and protein languages; carries specific amino acids to the ribosome where they are assembled into proteins. All 20 amino acids are found in the cytoplasm

Front 38

Codon

Back 38

3 nucleotide sequence that specifies a particular amino acid or termination signal in DNA or mRNA; basic unit of genetic code.

Front 39

Anticodon

Back 39

3 nucleotide sequence at one end of a tRNA molecule that recognizes a specific complementary codon on an mRNA molecule.

Front 40

Aminoacyl-tRNA synthetase

Back 40

An enzyme that joins each amino acid to the appropriate tRNA.
a) Specificity for each amino acid (20 amino-acyl-tRNA synthetases: 20 amino acids).

Front 41

Wobble

Back 41

Flexibility of the base-pairing rules in which the nucleotide at the 5’ end of a tRNA anticodon
can form H-bonds with more than one kind of base in the third position of a codon. 3 letter codon reads
1st 2, the 3rd one has the wiggle (wobble) room.
a) No specificity for each amino acid codon (61 amino acid codons: 45 tRNA’s)

Front 42

Ribosomes

Back 42

Complex of rRNA and protein molecules that function as a site of protein synthesis in the cytoplasm.
a) Composed of two subunits: large and small.

Front 43

rRNA (ribosomal)

Back 43

Molecules that, together with proteins, make up ribosomes; the most abundant type of RNA.
P site: Holds the tRNA carrying the growing polypeptide chain (protein).
A site: Holds the tRNA carrying the next amino acid to be added to the growing chain.
E site: Site from which empty tRNA’s exit.

Front 44

Building a Polypeptide

Back 44

Stage 1: Initiation
Stage 2: Elongation
Stage 3: Termination

Front 45

Stage 1: Initiation

Back 45

a) Small ribosomal subunit binds to mRNA.
b) Initiator tRNA base pairs with the start codon.
c) Large ribosomal subunit binds to form the ribosome.
d) The initiator tRNA waits in the P site for the next tRNA to occupy the A site.

Front 46

Initiation factors

Back 46

Protein factors that bring together all components for initiating protein synthesis.

Front 47

Translation initiation complex

Back 47

Completed assembly of mRNA, initiator tRNA, a small ribosomal subunit, and a large ribosomal subunit

Front 48

Stage 2: Elongation

Back 48

a) tRNA binds to a complementary mRNA in the A site.
b) A peptide bond is formed between the amino acid in the A site with the amino acid in the P site.
c) The tRNA in the P site is translocated to the E site and released while the tRNA in the A site is translocated to the P site.

Front 49

Elongation factors

Back 49

Proteins that assist in the addition of amino acids, one by one.

Front 50

Stage 3: Termination

Back 50

a) When a ribosome reaches stop codon on mRNA, the A site accepts a release factor.
b) Release factor promotes hydrolysis of the bond between tRNA in the P site and the last amino acid of the polypeptide.
c) All the components of the ribosomal assembly dissociate.

Front 51

Release factor

Back 51

Protein that binds directly to the stop codon (UAG, UAA, or UGA) adding a water molecule instead of an amino acid, hydrolyzing the bond between the completed protein and the tRNA in the P site

Front 52

Mutation

Back 52

Change in the nucleotide sequence of an organism’s DNA.
a) Usually due to radiation, chemicals, viruses

Front 53

Point mutation

Back 53

Change in a single nucleotide pair of a gene. Sickle-cell anemia
a) If it occurs in gametes, can be passed on to off-spring.
b) If it occurs in phenotype – genetic or hereditary disorder.

Front 54

Base-pair substitution

Back 54

Replacement of one nucleotide base pr. in the complementary DNA strand by
another pr. of nucleotides

Front 55

Silent mutation

Back 55

Change in nucleotide pr. may transform one codon into another, but for same amino acid

Front 56

Missense mutation

Back 56

Base pair substitution that results in a codon coding for a different amino acid

Front 57

Nonsense mutation

Back 57

Changes an amino acid codon to one of the stop codons, resulting in a shorter and usually nonfunctional protein

Front 58

Insertions/deletions

Back 58

Additions or losses of nucleotide pairs of genes.

Front 59

Frameshift mutations

Back 59

Occurs when the number of nucleotides inserted or deleted is not a multiple of three; realigns nucleotides into new codons. Proteins are usually not functional.

Front 60

Mutagen

Back 60

Chemical or physical agent that interacts with DNA and causes mutations.
examples: Chemicals, radiation, viruses.