Biology 10 Lecture
Chapter 25 - Molecular Basis of Inheritance
Roles of DNA & RNA
I.
Overview
A. DNA Structure & Replication
B. Gene Expression (DNA to RNA to Protein)
C. Control of Gene Expression
D. Gene Mutations
II. DNA Structure & Replication
A. _______ were known to be hereditary material in chromosomes in the cell nucleus by
the mid-1900s.
B. This hereditary material was found to be ______ (deoxyribonucleic acid) by Hershey
& Chase’s experiment:
1. Labeled some T2 virus _______ coats with radioactive 35S.
2. Labeled other T2 virus ______ with radioactive 32P.
3. Incubated labeled viruses with ___________ cells.
4. Found that the labeled _____, not the protein, entered the bacteria and produced
more viruses.
C. Structure of ______
1. DNA is composed of ___________ (phosphate, deoxyribose sugar, and a nitrogen
2.
3.
base)
DNA nitrogenous ________ include:
a. ____________ have a double ring structure and include adenine (__) and
guanine (__)
b. ____________ have a single ring and include thymine (__) and cytosine (__)
c. Chargaff found an equal amount of __________ and ____________ in DNA.
d. Amount of A =__ and amount of G =___.
Rosalind Franklin’s X-ray diffraction photograph showed that the DNA molecule
was a double ________.
D. Watson & Crick model of DNA
1. DNA consists of two strands of nucleotides, twisted together in a double
2.
3.
_________, like a twisted ladder.
Sugar-phosphate molecules make up the sides of the ladder, nitrogen ________
form the rungs.
Base pairs are _______________:
a. Purine Adenine (__) pairs with pyrimidine Thymine (__).
2
b.
4.
5.
Purine Guanine (__) pairs with pyrimidine Cytosine (__).
Weak ____________ bonds hold base pairs together.
Linear ____________ of bases can be in any order, providing great genetic
variability.
E. DNA ______________ - unzipping and recoupling bases
1. During ___ stage of interphase, DNA unwinds & “unzips.”
2. Helicase unwinds DNA & breaks the ____________ bonds between base pairs.
3. _____________ in nucleoplasm are joined to complementary bases of separated,
4.
5.
single DNA strands by DNA _________.
Two _____________ DNA double helices result.
Called semiconservative replication because each resulting double helix has one
_________ strand and one ____ strand.
III. _______ Expression (Protein Synthesis)
A. Overview (DNA  mRNA  tRNA + A.A.  Protein)
1.
2.
3.
4.
DNA in the nucleus is like a cookbook containing _______ “recipes” for
__________.
DNA unwinds at a gene and the “recipe” is rewritten (______________) as
messenger RNA (_____).
mRNA moves from nucleus to cytoplasm and is “clamped” onto the E. R. protein
assembly line by __________ (rRNA).
Transfer RNA (_____) then brings appropriate amino acid “ingredients” to
mRNA (___________) to make the protein.
B. Structure of _____
1. Mostly ____________-stranded, not helical.
2. Composed of nucleotides, but has ________ sugar instead of deoxyribose.
3. Thymine of DNA is replaced by _________ in RNA, thus adenine pairs with
uracil in RNA.
C. Three types of ______ in Protein Synthesis:
1.
_____ - carries coded sequence of bases in 3 base ______ from DNA in
nucleus to ribosomes in cytoplasm.
2.
______ - major component of ribosomes produced in the ________;
ribosomes bind mRNA during protein synthesis
3.
______ - carries an amino acid specific for its 3 base _____________ to a
complementary mRNA codon.
D. The Genetic Code
1.
The order of DNA bases ultimately codes for the order of _____ ________ in
proteins.
3
2.
The _________ code of four bases supplies 43=64 triplets, more than enough for the
___ amino acids.
3.
4.
A _______ is a “3 letter” unit of 3 nucleotides in ______.
5.
61 codons correspond to particular ______ _____ (usually more than one codon per
amino acid)
6.
7.
Three are _______ codons (UAA, UAG, UGA).
All 64 mRNA _____ have been determined, as to which ______ _______ will be
brought to them (see chart)
One codon (_____) for methionine is a _______ codon to begin protein synthesis.
E. _______________ - first stage in protein synthesis: DNA is “transcribed” to mRNA;
occurs in the ____________
1.
2.
A portion of DNA (________) unwinds and unzips.
3.
4.
RNA _________ pairs with DNA adenine.
5.
Processed mRNA exits nucleus through nuclear membrane pores to ____________ in
cytoplasm.
Complementary ______ nucleotides pair with DNA nucleotides of the sense strand,
via RNA ____________.
Resulting mRNA is processed by RNA ribozymes to remove ________ and leave
________ that will be expressed.
F. _____________ - second stage in protein synthesis in which the sequence of mRNA
nucleotide codons is “translated” into a specific sequence of amino acids brought by
tRNA (in the ______)
1.
2.
Initiation - ______ binds to a ribosome on the E. R.
Elongation
a. tRNAs with __________ complementary to mRNA _______ bring specific
______________ one at a time in the sequence dictated by mRNA.
b.
Each new amino acid forms a ___________ bond with the previous amino acid to
form the _______________ chain.
3.
Termination - Translation ends when tRNA binds to _______ codon on mRNA;
ribosomes dissociate from mRNA.
4.
______________ are several ribosomes that move along mRNA at one time, for
several polypeptides made at once.
G. ____________ of Gene Expression
1. DNA in the nucleus contains a ________ code; each group of 3 bases corresponds to
a specific amino acid
2.
During ______________, a segment (gene) of DNA serves as a template for the
formation of _______ (DNA  mRNA)
3.
mRNA carries its sequence of ________ to ribosomes in the cytoplasm
4
4.
During ____________, ______ with anticodons complementary to the mRNA codons
bring specific ___________ to the mRNA
5.
The linear sequence of the ______ codons determines the order of amino acids in the
resulting polypeptide.
IV. ___________ of Gene Expression
A. All cells receive the same DNA with the same _______, but cells differ as to which genes
they __________ (e.g.: Muscle cells have different genes “turned on” than nerve cells)
B. In __________ cells, several mechanisms regulate gene ________ from transcription to
protein activity. These mechanisms include
1.
In the ____________:
a.
Transcriptional control mechanisms during ______ transcription include the
organization of chromatin and the use of transcription _________ that initiate
transcription.
b.
Posttranscriptional control mechanisms after mRNA is formed include how
mRNA is ____________ before it leaves the nucleus and the speed at which it
leaves.
2. In the _____________:
a.
Translational control occurs before the ________ is formed; some mRNA
molecules survive longer than others, thus less protein is formed.
b.
Posttranslational control occurs after protein synthesis; the protein may have to
undergo additional _________ before it is functional.
C. ______________ Control in Eukaryotes involves the organization of chromatin and
regulatory proteins called transcription factors
1.
2.
Organization of ____________
a. Chromosomes must ____________ before a gene can be transcribed
b.
In ____________ chromosomes of vertebrate egg embryos, mRNA is synthesized
rapidly
c.
As the larvae develop, first one, then another region of the chromosomes bulge
out, forming chromosome _______, where the chromosome is decondensing
d.
This allows RNA _________ to attach to the section of DNA
Transcription factors are DNA binding __________
a.
Different cell types contain different transcription ________; a specific
combination is thought to regulate the activity of a particular gene
b.
After the right combination of transcription factors binds to DNA, an RNA
___________ attaches to the DNA and begins transcription
c.
As cells mature, they become ____________, determined by which ______ are
active and by which transcription _______ are present
5
d.
Signals received from outside and inside the cell may turn __ or ____ genes for
particular transcription factors
IV. Effects of Gene _____________ on Protein Synthesis
A.
B.
C.
Gene Mutation - change in the _________ sequence of a gene.
_______________ Mutation
1. One or more nucleotides is ________ or _______ from DNA.
2.
___________ frame (sequence of mRNA codons) is shifted (e.g., THE CAT ATE
THE RAT changed to THE ATA TET HER AT when C in CAT is deleted).
3.
4.
Shifted mRNA ______ sequence leads to incorrect amino acid sequence.
Usually results in nonfunctional ___________.
__________ Mutation
1.
2.
Change in one ________, results in a change in one ______.
May have one of three ___________:
a.
__________ Mutation - codon is changed to codon for the _______ amino
acid; no effect on protein.
b.
___________ Mutation - codon is changed to a premature ______ codon;
protein is too short and nonfunctional.
c.
_____________ Mutation - codon is changed to codon for a different
_______ _____; may or may not affect protein, depending on the properties of
the respective amino acids (e.g., change from polar __________ to nonpolar
______ in hemoglobin results in sickle-cell anemia)
D. Cause & Repair of Mutations
1. Mutations due to DNA replication errors are very rare because DNA ___________
“proofreads” and corrects the new strand
2.
__________ are environmental influences that cause mutations, such as radiation and
organic chemicals
3.
If mutagens cause a mutation in the ____________, then the organism’s offspring
may be affected
4.
If the mutation occurs in the individual’s body cells, _________ may result.