Transcript Chapter3

Chapter 3
Genetics: Cells and Molecules
Copyright © 2013 Pearson Education, Inc. All rights reserved.
Genetics
• The Study of Genetics
–Cellular and molecular genetics
–Classical and Mendelian genetics
–Population genetics
–Phylogenetics
–Behavioral genetics
Copyright © 2013 Pearson Education, Inc. All rights reserved.
The Cell
• The basic building
block of life
• Single celled
organisms
• Multicellular
organisms
• Prokaryotes
– No compartments for
genetic material
• Eukaryotes
– Separated genetic
material
Copyright © 2013 Pearson Education, Inc. All rights reserved.
Cell Anatomy (Eukaryotic)
• Nucleus
– Deoxyribonucleic Acid (DNA)
•
•
•
•
•
•
Gametes
Cytoplasm
Cell Membrane
Mitochondria
Ribosomes
Endoplasmic Reticulum
Copyright © 2013 Pearson Education, Inc. All rights reserved.
DNA Structure I: The Molecular
Level
• DNA Structure I: The Molecular Level
– Double Helix
– Nucleotide
• Sugar
• Phosphate
• Base
– Purines
» Adenine
» Guanine
– Pyrimidines
» Cytosine
» Thymine
Copyright © 2013 Pearson Education, Inc. All rights reserved.
DNA Function I: Replication
Separate Strands
Mutations
Enzymes
Proofreading and
Repair
Copyright © 2013 Pearson Education, Inc. All rights reserved.
The DNA Molecule

James Watson (left)
and Francis Crick in
1953 with their
model of the
structure of the DNA
molecule.
Part of a DNA Molecule
DNA Replication
The DNA Replication Process



Enzymes break the bonds between the DNA
molecule.
Two nucleotide chains serve as templates for the
formation of a new strand of nucleotides.
Unattached nucleotides pair with the appropriate
complementary nucleotide.
Protein Synthesis



Ribosomes help convert the genetic message from
the DNA into proteins.
Messenger RNA (mRNA) carries the genetic
message from the cell nucleus to the ribosome.
Transfer RNA (tRNA), found in the cytoplasm, binds
to one specific amino acid.
RNA and DNA
RNA differs from DNA in three important ways:
1. It’s usually single-stranded. (This is true of the forms
we discuss, but it’s not true for all.)
2. It contains a different type of sugar.
3. It contains the base uracil as a substitute for the
DNA base thymine. (Uracil is attracted to adenine,
just as thymine is.)
Messenger RNA (mRNA)


A form of RNA that’s assembled on a sequence of
DNA bases.
It carries the DNA code to the ribosome during
protein synthesis.
Codons

Triplets of messenger RNA bases that code for
specific amino acids during protein synthesis.
Transfer RNA (tRNA)

The type of RNA that binds to amino acids and
transports them to the ribosome during protein
synthesis.
Protein Synthesis: Transcription


The process of coding a genetic message for
proteins by formation of mRNA.
A portion of the DNA unwinds and serves as a
template for the formation of a mRNA strand.
Transcription
Transcription



The two DNA strands have partly separated.
Free messenger RNA (mRNA) nucleotides have been
drawn to the template strand, and a strand of
mRNA is being made.
Note that the mRNA strand will exactly complement
the DNA template strand, except that uracil (U)
replaces thymine (T).
Protein Synthesis: Translation




The mRNA travels through the nuclear membrane to
the ribosome.
tRNAs arrive at the ribosome carrying their specific
amino acids.
The base triplets on the tRNA match up with the
codons on the mRNA.
As each tRNA line up in the sequence of mRNA
codons their amino acids link to form a protein.
DNA Function II: Protein Synthesis
• Proteins
• Protein Synthesis
– Compose bone and
muscle
– Hormones
– Enzymes
– Cellular function
– Amino acids
– Dipeptides
– Polypeptide chains
Copyright © 2013 Pearson Education, Inc. All rights reserved.
DNA Function II: Protein Synthesis
(cont’d)
• Genetic Code
– Nucleotides
– Codons
– Genes
• Redundancy
• Transcription and
Translation
–
–
–
–
mRNA
tRNA
Introns
Exons
Copyright © 2013 Pearson Education, Inc. All rights reserved.
Cell Division


Cell division results in production of new cells.
During cell division:
 Cells
are involved with normal cellular and metabolic
processes.
 The cell’s DNA becomes tightly coiled.
 DNA is visible under a microscope as chromosomes.
Chromosomes
Scanning electron
micrograph of
human chromosomes
during cell division.
 Note that these
chromosomes are
composed of two
strands, or two DNA
molecules.

Chromosome Structure




A chromosome is composed of a DNA molecule and
associated proteins.
During normal cell functions, chromosomes exist as
single-stranded structures.
During cell division, chromosomes consist of two
strands of DNA joined at the centromere.
Since the DNA molecules have replicated, one
strand of a chromosome is an exact copy of the
other.
Chromosomes and Genetics

Each species is characterized by a specific number
of chromosomes.
 Humans

have 46 chromosomes.
Chromosome pairs are called homologus:
 They
carry genetic information that influences the same
traits.
 They are not genetically identical.
Types of Chromosomes


Autosomes - govern all physical characteristics
except sex determination.
Sex chromosomes - X and Y chromosome.
 Mammal
females have two X chromosomes.
 Mammal males have one X and one Y chromosome.
Mitosis



Mitosis is cell division in somatic cells.
Mitosis occurs during growth and
repair/replacement of tissues.
The result of mitosis is two identical daughter cells
that are genetically identical to the original cell.
Steps in Mitosis
1.
2.
3.
4.
The 46 chromosomes line up in the center of the
cell.
The chromosomes are pulled apart at the
centromere.
The strands separate and move to opposite ends
of the dividing cell.
The cell membrane pinches in and two new cells
exist.
Mitosis
The cell is involved in
metabolic activities.
 DNA replication
occurs, but
chromosomes are not
visible.

Mitosis

The nuclear
membrane
disappears, and
double-stranded
chromosomes are
visible.
Mitosis

The chromosomes
align themselves at
the center of the
cell.
Mitosis

The chromosomes
split at the
centromere, and the
strands separate
and move to
opposite ends of the
dividing cell.
Mitosis
The cell membrane
pinches in as the cell
continues to divide.
 The chromosomes
begin to uncoil (not
shown here).

Mitosis
After mitosis is
complete, there are
two identical
daughter cells.
 The nuclear
membrane is
present, and
chromosomes are no
longer visible.

Meiosis



Cell division in specialized cells in ovaries and
testes.
Meiosis involves two divisions and results in four
daughter cells, each containing only half the
original number of chromosomes.
These cells can develop into gametes.
Recombination

Sometimes called crossing over; the exchange of
genetic material between partner chromosomes
during meiosis.
Mitosis
Meiosis
•
•
Similar to the formal already present for the presentation of Mitosis
Meiosis is ultimately more important to understand, so it is even more
deserving of a detailed presentation
Evolutionary
Significance of Meiosis



Meiosis and sexual reproduction are highly
important evolutionary innovations.
Meiosis increases genetic variation at a faster rate
than mutation.
Offspring in sexually reproducing species represent
the combination of genetic information from two
parents.
Problems with Meiosis



In order for fetal development to occur normally,
the meiotic process needs to be exact
If chromosomes or chromosome strands do not
separate during either of the two divisions, serious
problems can develop
Failure to separate is called nondisjunction
DNA Structure II: Chromosomes
and Cell Division
• Chromatin State
• Chromosomes form
• Mitosis
– Centromere
– Diploid somatic cells
– Haploid sex cells
• Meiosis
– Somatic cell division
– Sex cell division
Copyright © 2013 Pearson Education, Inc. All rights reserved.
DNA Structure II: Chromosomes
and Cell Division (cont’d)
• Mitosis
–
–
–
–
–
Interphase
Prophase
Metaphase
Anaphase
Telophase
• Meiosis
–
–
–
–
–
Tetrad formation
Crossing over
Recombination
Reduction division
Second Meiotic Division
Copyright © 2013 Pearson Education, Inc. All rights reserved.
Chromosomal Abnormalities
• Nondisjunctive Errors: The failure of
homologous chromosomes to separate
properly during cell division
– Monosomy
• Turner Syndrome
– Trisomy
• Down’s Syndrome
Copyright © 2013 Pearson Education, Inc. All rights reserved.
Molecular Tools for
Bioanthropological Research
• Indirect Methods
– Immunological Methods
– DNA Hybridization
• Direct Methods
– DNA Sequencing
– Protein Sequencing
Copyright © 2013 Pearson Education, Inc. All rights reserved.
Molecular Tools for
Bioanthropological Research (cont’d)
• PCR
• Mitochondrial DNA (mtDNA)
• Ancient DNA
Copyright © 2013 Pearson Education, Inc. All rights reserved.
Molecular Tools for
Bioanthropological Research (cont’d)
• Polymerase Chain Reaction
– The polymerase chain reaction (PCR) is a method
for the amplification of minute quantities of DNA
– PCR makes possible the recovery of ancient DNA
from bone or fossil material, up to about 100,000
years old, provided that preservation conditions
were adequate
Copyright © 2013 Pearson Education, Inc. All rights reserved.