BBS1005 Case 1-6 Summary
By Grace Marshall and Nile Verleur
PBL Case 1- Age and reproducton
Learning Goals
- Structure of DNA and the basics of replicaton no notes!)
- 3’-5’, antparallel, nucleotdes, basic mitosis
- Different mutatons that can occur in DNA presentaton ready)
- Both DNA and Chromosomal level
- Repair mechanisms of mutatons
- Process of Meiosis, focus on when mutatons occur and their impacts
- Stages, difference to mitosis
- Gametogenesis- the difference between males and females
- Effect of age on gametogenesis and reproducton
- Higher chance of mutatons, tmeline for gametes, late stage fertlity
Revision of BBS1001 Case 2
The structure of DNA
A DNA molecule consists of two long antparallel polynucleotde chains composed of four types of
nucleotde subunits
- The nucleotde subunits consist of a phosphate group, a deoxyribose sugar and a nitrogenous
base
- Either the bulkier two ring purines Adenine and Guanine, or the smaller single ring
pyrimidines Cytosine and Thymine. There is complementary base pairing; A to T 2
hydrogen bonds), G to C 3 hydrogen bonds).
- The sugar and phosphate group form the backbone of the DNA. The phosphate group on C5 of
the deoxyribose sugar and the hydroxyl group on C3 on the sugar of a different nucleotde can
form phosphodiester bonds to create the backbone
- This gives the DNA strand a polarity- one backbone will have the phosphate on C5 at the
end, and thus, be referred to as the 5' end, whilst the other will have the hydroxyl group
on C3 and be the 3' end.
- The complementary base pairing gives rise to double helix 3D structure of DNA, as each pair of
, nucleotdes is the same width. The helix goes through one full rotaton every ten pairs.
- The structure of DNA lead to the theory of semi conservatve replicaton- as each strand was
exactly complementary to the other, they could both act as a template for a new daughter
strand.
,Semi Conservatve Replicaton
- Semi conservatve means one backbone is used as a template strand for each new molecule
a. The supercoil is removed by the enzyme topoisomerase.
- This is through the separaton and reconnecton of the sugar-phosphate
backbone
b. DNA gyrase moves in advance of helicase and relieves strains in the DNA molecule that
form when the double helix uncoils
c. Helicase uncoils the DNA double helix by breaking the weak hydrogen bonds at the
origin of replicaton TATA region)
- The strands are separated into two template strands, and kept apart with single
strand binding proteins
- This leads to the formaton of the replicaton fork
- Due to the antparallel structure of DNA, the strands have to be
replicated in different ways
- The Leading Strand is in the 5’-3’ directon, so is read and thus
replicated contnuously in the 3’-5’ directon
- This means the new strand is created is in the 5’-3’
directon
- The Lagging Strand is in the 3’-5’ directon so must be
discontnuously replicated in the 5’-3’ directon
d.
e. RNA Primase synthesizes primers of about 20 nucleotdes length consistng of RNA in 5’-
3’ directon
- This ataches to the helicase to form a primosome
- This primer will later be removed by 5’-3’ Exonuclease. Do not get it confused
with 3’-5’ exonuclease.
f. DNA Polymerase III polymerises free nucleotdes found in the nucleus in the 5’ to 3’
directon 3’ to 5’ on the template strand)
- in the directon of the replicaton fork for the leading strand
- On the lagging strand:
, - Fragments with primer-RNA and DNA called okazaki fragments form
- After the fragment is created, DNA Polymerase I replaces the RNA
Primer with DNA nucleotdes
- Once two fragments are ready, they are atached with phosphodiester
bonds by DNA Ligase
g. 3’-5’ exonuclease proofreads the new DNA in 3’-5’ directon for possible errors
DNA Topoisomerase prevents DNA tangling during replicaton. Topoisomerase I produces a single strand
break in the phosphodiester backbone, allowing the two sectons of DNA helix on either side of the nick
to rotate freely relatve to each other. Topoisomerase II can separate two interlocked DNA circles to
prevent severe DNA tangling problems.
Mutatons
Mutatons are heritable changes to the sequence of nucleotdes in DNA molecules. They
can occur in DNA during the replicaton and cell division process. Environmental factors that increase
the rate of mutaton are known as mutagens, and include the ultraviolet in the rays from the sun.
Gene mutatons can be classifed in two major ways:
- Hereditary germline) mutatons
- Inherited from a parent
- Present throughout a person’s life in virtually every cell in the body.
- Acquired or somatc) mutatons
- Occur at some tme during a person’s life
- Present only in certain cells, not in every cell in the body
- Caused by environmental factors such as ultraviolet radiaton from the sun, or can occur
if an error is made as DNA copies itself during cell division.
Within this, there are different classes of DNA mutatons:
- Missense mutaton
- A change in one DNA base pair that results in the substtuton of one AA for another in
the protein made by a gene.
By Grace Marshall and Nile Verleur
PBL Case 1- Age and reproducton
Learning Goals
- Structure of DNA and the basics of replicaton no notes!)
- 3’-5’, antparallel, nucleotdes, basic mitosis
- Different mutatons that can occur in DNA presentaton ready)
- Both DNA and Chromosomal level
- Repair mechanisms of mutatons
- Process of Meiosis, focus on when mutatons occur and their impacts
- Stages, difference to mitosis
- Gametogenesis- the difference between males and females
- Effect of age on gametogenesis and reproducton
- Higher chance of mutatons, tmeline for gametes, late stage fertlity
Revision of BBS1001 Case 2
The structure of DNA
A DNA molecule consists of two long antparallel polynucleotde chains composed of four types of
nucleotde subunits
- The nucleotde subunits consist of a phosphate group, a deoxyribose sugar and a nitrogenous
base
- Either the bulkier two ring purines Adenine and Guanine, or the smaller single ring
pyrimidines Cytosine and Thymine. There is complementary base pairing; A to T 2
hydrogen bonds), G to C 3 hydrogen bonds).
- The sugar and phosphate group form the backbone of the DNA. The phosphate group on C5 of
the deoxyribose sugar and the hydroxyl group on C3 on the sugar of a different nucleotde can
form phosphodiester bonds to create the backbone
- This gives the DNA strand a polarity- one backbone will have the phosphate on C5 at the
end, and thus, be referred to as the 5' end, whilst the other will have the hydroxyl group
on C3 and be the 3' end.
- The complementary base pairing gives rise to double helix 3D structure of DNA, as each pair of
, nucleotdes is the same width. The helix goes through one full rotaton every ten pairs.
- The structure of DNA lead to the theory of semi conservatve replicaton- as each strand was
exactly complementary to the other, they could both act as a template for a new daughter
strand.
,Semi Conservatve Replicaton
- Semi conservatve means one backbone is used as a template strand for each new molecule
a. The supercoil is removed by the enzyme topoisomerase.
- This is through the separaton and reconnecton of the sugar-phosphate
backbone
b. DNA gyrase moves in advance of helicase and relieves strains in the DNA molecule that
form when the double helix uncoils
c. Helicase uncoils the DNA double helix by breaking the weak hydrogen bonds at the
origin of replicaton TATA region)
- The strands are separated into two template strands, and kept apart with single
strand binding proteins
- This leads to the formaton of the replicaton fork
- Due to the antparallel structure of DNA, the strands have to be
replicated in different ways
- The Leading Strand is in the 5’-3’ directon, so is read and thus
replicated contnuously in the 3’-5’ directon
- This means the new strand is created is in the 5’-3’
directon
- The Lagging Strand is in the 3’-5’ directon so must be
discontnuously replicated in the 5’-3’ directon
d.
e. RNA Primase synthesizes primers of about 20 nucleotdes length consistng of RNA in 5’-
3’ directon
- This ataches to the helicase to form a primosome
- This primer will later be removed by 5’-3’ Exonuclease. Do not get it confused
with 3’-5’ exonuclease.
f. DNA Polymerase III polymerises free nucleotdes found in the nucleus in the 5’ to 3’
directon 3’ to 5’ on the template strand)
- in the directon of the replicaton fork for the leading strand
- On the lagging strand:
, - Fragments with primer-RNA and DNA called okazaki fragments form
- After the fragment is created, DNA Polymerase I replaces the RNA
Primer with DNA nucleotdes
- Once two fragments are ready, they are atached with phosphodiester
bonds by DNA Ligase
g. 3’-5’ exonuclease proofreads the new DNA in 3’-5’ directon for possible errors
DNA Topoisomerase prevents DNA tangling during replicaton. Topoisomerase I produces a single strand
break in the phosphodiester backbone, allowing the two sectons of DNA helix on either side of the nick
to rotate freely relatve to each other. Topoisomerase II can separate two interlocked DNA circles to
prevent severe DNA tangling problems.
Mutatons
Mutatons are heritable changes to the sequence of nucleotdes in DNA molecules. They
can occur in DNA during the replicaton and cell division process. Environmental factors that increase
the rate of mutaton are known as mutagens, and include the ultraviolet in the rays from the sun.
Gene mutatons can be classifed in two major ways:
- Hereditary germline) mutatons
- Inherited from a parent
- Present throughout a person’s life in virtually every cell in the body.
- Acquired or somatc) mutatons
- Occur at some tme during a person’s life
- Present only in certain cells, not in every cell in the body
- Caused by environmental factors such as ultraviolet radiaton from the sun, or can occur
if an error is made as DNA copies itself during cell division.
Within this, there are different classes of DNA mutatons:
- Missense mutaton
- A change in one DNA base pair that results in the substtuton of one AA for another in
the protein made by a gene.
