Download DNA Replication

Introduction
 We can use DNA and genetics to reconstruct
relationships with living and fossil ancestors
 It will show how we are related to other primates
 It will help us understand diseases and how they are
transmitted
The Cell
 Prokaryotes are one-celled organisms
 Eukaryotes are multi-celled organisms
 Also have a nucleus and cytoplasm
 Types of cells (important!!):
 Somatic cells: body cells, use mitosis
 Gametes: sex cells, sperm/egg, use meiosis
DNA Molecule
 Think of a cell
 Zoom into the middle, in the nucleus
 In the nucleus are chromosomes
 Inside the chromosomes are bundles of DNA
 DNA forms sequences or codes that give the body
instructions
 The complete set of genes in an individual is a genome
DNA and Chromosomes
 Chromosome number is species-specific!
 Examples:
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Camel: 70
Salamander: 24
Apple: 34
Algae: 148
Colobus Monkey: 44
Orangutan: 48
Human 46
Chromosomes
 A healthy human has 46 chromosomes, in 23 pairs.
Why are they in pairs?
 DNA is homoplasmic: every cell in the body has the
exact same, complete set of DNA
 Mitochrondrial DNA is different and used to trace
ancestry.
 Inherited 100% through mother’s line
 Heteroplasmic: it can differ within in body
Chromosome Types
 Chromosomes are homologous, meaning they are in
pairs, with the same information on the same
locations
 The first 22 (pairs of) chromosomes are autosomes
 The 23rd pair are sex chromosomes (XX or XY)
 All chromosomes lined up in order is a karyotype
DNA: Blueprint for Life
 DNA is the instruction manual for the body
 What shape does DNA have?
 The sides are made of sugar (deoxyribose) and
phosphate
 The “rungs” are made of 4 bases: adenine, thymine,
cytosine, guanine or A, T, C, G
 Complementary bases
 Specific pairing:
 A ALWAYS BONDS WITH T
 C ALWAYS BONDS WITH G
DNA Replication
 Cells must make more of themselves
 Makes identical copies if it is a somatic cell
 In order to do this, the FIRST STEP IN CELL DIVISION IS
ALWAYS DNA REPLICATION
 The bonds between A/T and C/G are broken and the
ladder unzips
 The lonely letters look for their complementary partner: A
for T and C for G
 When they attach to free floating letters, they have made
two identical ladders and have replicated
Hmmm…
 Now, if a cell has 46 chromosomes in it
 And we have done DNA replication,
 Then that cell will have double the number of
chromosomes…it will have 92
 Is this normal? How do we get it back to 46?
Mitosis
 Somatic cells have all 46 chromosomes. They are
diploid in number
 To make more, we use mitosis:
 After DNA replication, when the cell has 92
chromosomes, it pinches apart and becomes 2 cells,
each identical, each with 46 chromosomes
Gametes
 Gametes are different
 How much genetic information can you pass down
to your offspring?
 Therefore, gametes have HALF the number of
chromosomes: 23. They are haploid in number
Meiosis
 Gametes make new cells by meiosis
 The first step is still____________________!!!
 They now have 92 chromosomes
 They divide once (just like mitosis) and have 46
 But they MUST DIVIDE A SECOND TIME to end up
with 23 chromosomes in each cell (sperm or egg)
created
Variation
 During meiosis the body can try to add variation
 Crossing over and recombination are reshuffling of
the genetic material just before division
 Sometimes there can be errors
 Translocations rearrange chromosome information but
can insert or delete information
 Nondisjunction means that an even number of
chromosomes does not get divided into each cell
Trisomy 21
 Nondisjunction can create Trisomy 21, in which 3
chromosomes are created at the 21st spot
 This is known as Down Syndrome
Protein Synthesis
 DNA is also used in creating proteins, which help in
growth, function, and repair of tissues
 They are made of amino acids, half of which are
made in the body and half of which come from food
 Proteins can be structural: responsible for physical
features (hair, eye color, bone shape) or regulatory
(hormones, enzymes, antibodies)
Protein Synthesis
 Has two parts:
 I. Part I is Transcription
 II. Part II is Translation
Transcription
 Begins just like DNA replication
 Enzyme splits the bonds of A, T, C, G
 BUT, instead of bonding and replicating, one strand
bonds in a different way:
 C bonds with G but A bonds with U (uracil)
 If a U is involved, it is protein synthesis
 The U creates RNA, which is smaller than DNA
 mRNA (messenger) is the product formed in this
stage
Transcription
 The mRNA is small enough to leave the nucleus and
go to the ribosome
 It carries the message in the form of 3 letter codons
 Examples: AUG, GCC, AUA, UAC
Translation
 In the ribosome, the mRNA codons are met by tRNA
(transfer RNA) anticodons that match letters
 Example: mRNA codons
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tRNA anticodons
CCG, UAG, CUG
GGC, AUC, GAC
 These matchings “translate” the code until an stop
codon makes them stop (like a period in a sentence).
 These form amino acids in long chains
 The chains keep winding and coiling to form
proteins, which have unique 3D shapes
Regulation
 Other than Replication and Protein Synthesis, DNA’s
function is regulation
 These codons start or stop certain functions
 DNA has a high degree of stability
 Mutations do occur, but the error rate in replication
is 1 in 10 billion!
 A lot of our DNA is inactive: about 98% of our DNA is
not actively doing anything
Blood Type
 Blood is unique: it has 4 phenotypes but 6
genotypes:
 Phenotype
Genotype
 Type A
AA or AO
 Type B
BB or BO
 Type AB
AB
 Type O
OO
Blood Type
 You get your blood type from antigens
 Antibodies will attack foreign particles, so the letters
must match in blood donation or agglutination
occurs
 A and B are dominant and share dominance: they
are codominant
 O is recessive (it is neutral and has no antigens)
Blood Type
 To donate, letters must match!
 Type A can give/receive if it has an A (AA, AO), or O
(it is neutral)
 Type B can give/receive if it has a B (BB, BO), or O (it
is neutral)
 Type AB can receive from anyone (AA, BB,
AB AB, O is neutral) but can only give to itself
 Type O can give to anyone (O is neutral), but can
only receive itself
Blood Type
 Who is the universal donor?
 Who is the universal recipient?
Punnett Square Review
 For the trait for ‘handedness’ (right-handed or lefthanded), right-handed is dominant
 Mother is left-handed and father is homozygous for
right-handed. What is the chance their offspring will
be left-handed?
Punnett Square
 A regular punnett square has the same letter, just
uppercase or lowercase; for blood type, this is the
only time the square will have different letters
 Let’s do a problem with blood type
 Sharon just had a baby and doesn’t know who the
father is.
 Sharon: Type A
Guy 1: Type AB
 Baby: Type O
Guy 2: Type B
 Can we say who IS NOT the father?
 First, write out the possible genotypes:
 Sharon: AA or AO
 Guy 1: AB
 Guy 2: BB or BO
 Baby: OO
 Is there anyone who could not be the father?
 Yes, Guy 1 because both the mother and the father would
have to give the baby an “O”
 Using this, what is Sharon’s genotype?
 It has to be AO, to give the baby an “O”
 Now let’s see if Guy 2 could be the father:
 Punnett Square:
 Put Sharon’s alleles across the top and Guy 2’s down the
side:
A
O
B
AB
BO
O
AO
OO
 The last box show that there is a chance (1/4 or 25%) that
Sharon and Guy 2 gave the baby O alleles, so Guy 2 could be
the father
More Practice
 The Punnett Square and the letters you fill in are the
genotypes
 The end result that we can describe is the phenotype
 Example 2:
 Red is dominant in rose color
 A red rose (homozygous dominant) and a white rose
have what chance of producing white roses?
Answer
 Homozygous dominant (red) = RR
 Homozygous recessive (white) = rr
R
R
Rr
Rr
Rr
Rr
r
r
There is a 0% chance of making white (recessive) roses
because each box has at least one dominant (red) R
Questions
 Why are there two types of cell divisions (mitosis
and meiosis)?
 Why does mitosis use DNA and protein synthesis use
RNA? How are they different?
 What is the difference between a genotype and
phenotype?
 Who is the universal donor and recipient?