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DNA
"The Blueprint of Life"
DNA stands for...
DeoxyriboNucleic Acid
●established by
James Watson
and Francis Crick
●Shape of a double
helix
●codes for your genes (traits)
●made of repeating subunits called
nucleotides
What is the relationship between GENES and DNA?
What is a gene?
A section of DNA, with
many bases that codes for
a protein
Results in a
TRAIT
What is a nucleotide?
Has three parts:
PHOSPHATE
DEOXYRIBOSE (sugar)
BASE (A,T,G,C)
Phosphate
Base
Sugar
There are two types of Bases
Purines (double-ring) – Adenine and Guanine
Pyrimidines (single-ring) –
Thymine, Cytosine, and Uracil
Base-Pair Rule
Adenine <==> Thymine
Guanine <==> Cytosine
The sides of the DNA
ladder are phosphate
& sugar
held together
by hydrogen bonds
Base Pair Rule
One side:
Other side:
A T A
T C A
T G C
G G G
How the Code Works
The combination of A,T,G,C determines what
traits you might have.....
C A T C A T = purple hair
T A C T A C = yellow hair
Think of the bases of DNA like letters.
Letters form words....
Words form sentences....
*endless
combinations
Let's Review What We Know About DNA
1. DNA stands for: De _____ ribo ______ acid
2. What is the shape of DNA? ______________
3. Who established the structure of
DNA? ____________ and ______________
4. Adenine always pairs with _______________
5. The sides of the DNA ladder are deoxyribose
and _______________
6. Guanine always pairs with _____________
7. What is the complementary sequence:
C
A
T
T A G
8. The two sides of DNA are held together by
_______ bonds.
9. DNA is composed of repeating subunits called
______________________
10. What are the 4 bases that make up the rungs
of the DNA ladder? ____________________
RNA
RNA = ribonucleic acid.
RNA is similar to DNA except:
1. typically has one strand instead of two strands
(can be double-stranded – viruses)
2. has uracil instead of thymine
3. has ribose instead of deoxyribose
RNA
Central Dogma
There are 3 main processes that define the
Central Dogma.
1. Replication – DNA is copied
2. Transcription - RNA is made from DNA
3. Translation - Proteins are made from the
message on the RNA
There are two other parts of the
central dogma, which are important for
viruses
• Reverse transcription – The process of making
a double stranded DNA molecule from a single
stranded RNA template through the enzyme,
reverse transcriptase.
• RNA replication - RNA-dependent RNA
polymerase is an essential protein encoded in the
genomes of all RNA-containing viruses with no
DNA stage that have anti-sense RNA. It
catalyses (makes happen) synthesis of the RNA
strand complementary to a given RNA template.
Central Dogma
DNA REPLICATION
the process by which DNA makes a copy of itself
(cell division)
SEMI-CONSERVATIVE - half of the old strand is saved
DNA Synthesis
The synthesis of new DNA strands complementary
to both strands of the parental molecule posed an
important problem to understanding the
biochemistry of DNA replication. Since the two
strands of double-helical DNA run in opposite
(antiparallel) directions, continuous synthesis of two
new strands at the replication fork would require
that one strand be synthesized in the 5′ to 3′
direction while the other is synthesized in the
opposite (3′ to 5′) direction. DNA is replicated using
several enzymes (proteins that do stuff – names
usually end in –ase).
DNA 5’ to 3’
https://www.youtube.com/watch?v=p835L4HWH68
DNA Replication
1. DNA helicase unzips the two strands of DNA
2. DNA polymerase III attaches free DNA nucelotides together But DNA polymerase assembles DNA only in the 5′ to 3′
direction. The new 5’ to 3’ strand is known as the leading
strand. How, then, can the other strand of DNA be
synthesized?
3. RNA primase attaches a RNA primer to the lagging strand (3’
to 5’).
4. DNA polymerase III can then attach to the lagging strand and
copy a short fragment of DNA (Okazaki fragments)
5. The RNA primers are then replaced by DNA by DNA
polymerase I.
6. The fragments of DNA are joined together by DNA ligase
7. There are now two complete new strands of DNA
DNA Replication
https://www.youtube.com/watch?v=dKubyIRiN84
HOW PROTEINS ARE MADE
BY THE CELL
What is a protein
and why is it
important for living
systems?
Your body is made up of
trillions of cells, of all different
kinds: muscle cells, brain cells,
blood cells, and more. Inside
those cells, proteins are
allowing your body to do what
it does: break down food to
power your muscles, send
signals through your brain that
control the body, and transport
nutrients through your blood.
Proteins are building
blocks, they make up all
that you are.
How Proteins are made by the cell:
There are 4 kinds of RNA. 3 of these are
used in protein synthesis
1. Messenger RNA (mRNA) – carries an
RNA version of a gene to a ribosome in
order to make a protein.
RNA carries the
"message" to the
ribosomes, where
proteins are made
4 Types of RNA
2. Transfer RNA (tRNA) – carries amino acids to a
ribosome to build a protein. On one end, it has a
segment called an anticodon. Each tRNA has an
anticodon that matches a specific codon on the
mRNA. On the opposite end of the tRNA is an
amino acid. When tRNA is made, a specific
amino acid is attached depending on what
anticodon it has.
tRNA
4 Kinds of RNA
3. Ribosomal RNA (rRNA) forms part of the ribosome.
Molecules of rRNA are synthesized in the nucleolus,
which contains the genes that encode rRNA. The
encoded rRNAs are either large or small. In the
nucleolus, the large and small rRNAs combine with
ribosomal proteins to form the large and small
subunits of the ribosome (e.g., 50S and 30S,
respectively, in bacteria). Ribosomal proteins are
synthesized in the cytoplasm and transported to the
nucleus to be assembled into subunits in the
nucleolus. The subunits are then returned to the
cytoplasm for final assembly
rRNA cont
In eukaryotes, anywhere from 50 to 5,000 sets of
rRNA genes and as many as 10 million ribosomes
may be present in a single cell. In contrast,
prokaryotes generally have fewer sets of rRNA
genes and ribosomes per cell. For example, in the
bacterium Escherichia coli, seven copies of the
rRNA genes synthesize about 15,000 ribosomes
per cell. Differences in rRNA are used to determine
evolutionary relationships between bacteria,
archaea, and eukaryotes.
Ribosome Subunits
4 types of RNA
4. siRNA – Small interfering RNA – plays a large
role in gene expression
Transcription
1. One of the strands of DNA is
used as a template to create a
strand of mRNA
2. Requires the enzyme RNA
polymerase
3. Transcription always
starts at a region called
the promoter.
4. Introns are segments of DNA that do not contain genes.
Exons are segments that contain genes.
5. Each 3 bases on mRNA is a codon, it corresponds to an
amino acid (see codon chart)
Translation
1. Takes the message
on mRNA and converts
it into an amino acid
chain
2. Individual amino acids will join to form a
protein. Shapes and composition of protein
determine its functionality (hair, enzymes, skin,
muscles etc)
Label the image....
amino acids
DNA
tRNA
protein
anticodon
mRNA
Label the image....
codon
ribosome
Steps in Translation
1. The ribosome binds to mRNA at a specific area.
2. The ribosome starts matching tRNA anticodon
sequences to the mRNA codon sequence.
3. Each time a new tRNA comes into the ribosome,
the amino acid that it was carrying gets added to
the elongating polypeptide chain.
4. The ribosome continues until it hits a stop
sequence, then it releases the polypeptide and the
mRNA.
5. The polypeptide forms into its native shape and
starts acting as a functional protein in the cell.
The steps in translation