Transcript Molecular Basis of Heredity DNA Instructions are inherited (passed) from parent to offspring in the form of a genetic code known as genes DNA:

Molecular Basis of Heredity
DNA
Instructions are inherited (passed) from parent
to offspring in the form of a genetic code
known as genes
DNA: Molecules that carry the genetic code.
The code is used to make PROTEINS
The proteins become cell parts and carry out
most functions of the cell.
DNA Molecule
Genes are made up of molecules of DNA:
“Deoxyribonucleic acid”
Found in nucleus.
Controls manufacture of enzymes, proteins
Made up of repeating subunits known as
nucleotide subunits.
The nucleotide is made of 3 “parts”
1. Phosphate group
(“sides” of the ladder)
2. A sugar, called “deoxyribose”
3. Nitrogenous base (the “rungs of the ladder”)
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The double helix
Nucleotides - DNA
Nitrogenous base:
Adenine “A” (always pairs with “T”)
Thymine “T” (always pairs with “A”)
Guanine “G” (always pairs with “C”)
Cytosine “C” (always pairs with “G”)
Forms the “rung” of the ladder
DNA Replication
During reproduction DNA makes exact copies of itself
called REPLICATION.
Occurs in nucleus during both mitosis and meiosis.
DNA polymerase (an enzyme!) causes the two
strands (sides) to “unzip”: the bonds between the
base pairs break
TEMPLATE: Each side serves as a pattern or
template. Each base pair will attract the
complementary nucleotide A—T or G—C
The two DNA strands will be identical
Genetic Code
Genetic Code: Heredity information
--depends upon the order of the nucleotides
in the DNA molecule.
--determines which type of protein is made
Gene: the sequence of nucleotides that
make the protein
Triplet codes: group of three nucleotides that
is specific to each amino acid.
also known as a CODON
RNA and Protein Synthesis
DNA provides the instruction to make proteins
But . . . DNA is too large to pass through the
nuclear membrane (double strand too BIG) How
will it get the instructions out of the nucleus?
RNA!
RNA exists as a single strand which is small
enough to pass through nuclear membrane
Messenger “mRNA” is made in the
nucleus
They serve as “messengers” from DNA to
the ribosome.
RNA base pairing:
Cytosine—Guanine C—G
Adenine—Uracil
A—U (not T!!)
Really important!!
RNA- Ribonucleic acid
DNA
RNA
Sugar: deoxyribose
Sugar: ribose
Nitrogen bases: adenine,
thymine, cytosine,
guanine
Double-stranded
Nitrogen bases: adenine,
cytosine, guanine and
uracil instead of thymine
Single-stranded
Only one kind of DNA
Three kinds:
messenger RNA (mRNA),
ribosomal RNA (rRNA),
transfer RNA (tRNA)
Ribosomal RNA makes up the major
portion of the Ribosome (the site of protein
synthesis) Location: cytoplasm!
Transfer RNA transfers amino acids to the
ribosome during protein synthesis
Protein Synthesis
DNA
transcription
(nucleus)
mRNA
translation
(cytoplasm)
Protein
The order of the bases in the DNA specifies
the order of bases in the mRNA, and
The order of bases in the mRNA specifies
the order of amino acids in a protein.
Transcription
RNA polymerase (an enzyme!) binds to the DNA
and separates the DNA strands
One strand of the DNA acts as a template from
which nucleotides are assembled into a strand
of mRNA.
This strand is complementary to the DNA,
except that uracil binds to adenine not thymine!
(BTW, what happens to the other strand of DNA?)
Protein Synthesis
REMEMBER: The RNA is only single
stranded!
The mRNA may now pass through the
nuclear membrane into the cell and over to
the ribosome
Translation
During translation, the mRNA transported
to the cytoplasm is "de-coded" or
"translated" to produce the correct order of
amino acids in a protein
Nucleotides on mRNA are read "three at
a time" (3= codon) by the ribosome
The mRNA will bind with tRNA at the
codons
Translation
tRNA = transfer RNA; small RNA molecules that
carry a specific amino acid at one end and an
anticodon region that recognizes and binds to
the codon (mRNA) at the other end. The tRNA.
The codon of the mRNA determines what amino
acid is added to a protein chain.
The process continues, chaining the amino
acids together until the “stop” codon is reached
Codon – anti codon
Lysine
Methionine
Anti-codon
codon
Changing Chromosome Structure
Translocation: transfer of one section of a
chromosome
Addition: a portion of one chromosome is
attached to another chromosome
Deletion: a portion of a chromosome is taken
away from a chromosome
Inversion: a portion of a chromosome breaks off
and then becomes reattached to the same
chromosome in an inverted (upside down)
fashion