Download Hemoglobin: Structure

So, Just Where Are We?
Our course is concerned with US, where we
came from, why we look and behave the way
we do.
In order to explore these issues, one of the first
things that has to be done is to focus on us as
humans, distinct from the rest of the animal
world.
Thus, over the past two weeks, we have looked
at the pattern of human distinctiveness, in
biology, behavior and language. It is
necessary that we begin our investigations of
Humans as Biologically
Unique
• Two weeks ago, we
explored the biological
features that make us
unique, including our erect
posture, our large brains
and our lack of projecting
canine teeth.
• The chimpanzee film gives
you an idea of just how
different and similar we are
to each other and sets in
dramatic focus our
evolutionary relationships
with these African apes.
• Now, it is time to look at
what we represent as a
species.
Humans as a variable species
All modern humans are
part of a single species:
Homo sapiens (we can
all interbreed and
produce fertile
offspring). However, as
we have already seen,
we also differ in many
biological features.
Today, we begin our
second section, dealing
with variation: what is
the nature and causes
of human biological,
social and linguistic
variation?
Human Variation 1.
There are all sorts of differences amongst
humans, and we are all aware that people
vary in facial and body features. We also
know that these differences extend to the
genetic materials themselves.
Indeed, there are parts of the human
genome that are so hypervariable that
examination of these specific locales can
identify specific individuals with a 1 in 88,000
chance of mistaking one person with another.
Human variation I
Human Variation II
Human Population Variation
• All humans vary (except for identical twins, but that is a
specific case, and usually by adulthood, there are differences
resulting from environmental influences).
• This variation is the result of the complex interaction of genetic
and environmental influences, but also random forces.
• It is clear that biological features are NOT randomly distributed
across the human landscape but have specific geographic
distributions. This is the basis for the simplistic notions of race
that are used in social interactions.
• It is equally clear that most of the human variation that we
observe is the result of human evolution to meet the needs of
specific environmental demands, like climate, food, altitude
and many other variables.
Genetics: The source of
variability for evolution
The basis for much of the variability we see in
modern humans originates in our genetic
material.
Like all living things, humans possess a
genetic structure based on DNA and its ability
tocode for a huge class of functioning
molecules: Proteins.
Our genetic structure has been formed over
millions of years of evolutionary change.
Our focus today: how population survival
What does the genetic
material do, anyway?
• The genetic material has a number of crucial
functions:
1. Transmit genetic information from one
generation to the next (humans produce human
infants and not rats or elephants).
2. Since every cell in the body (with several
exceptions) has more or less the same genetic
material as the original cell (the fertilized egg), the
genetic material must be able to reproduce itself
when new cells are produced during growth and
development as well as normal body maintenance.
3. The genetic materials are organized around a
sequence of chemical ‘bases’ that encode for the
synthesis of proteins, a huge class of chemicals that
What determines cell structure
and function?
• Proteins that are
expressed
• Unique expression
by cell type
• How is this
controlled?
• Look to the cell
nucleus
Chromosomes
• Carries information as
part of their structure
• Name=colored bodies
when stained and seen
microscopically
• Species-specific
number in each cell
nucleus, with the
chromosome number
usually expressed in
pairs (the complexity of
the living thing is not
reflected in the
chromosome number
(chimps, for example,
have more
Human chromosomes
• Species specific
number=46
• 23 pairs of chromosomes
• Specifially:
• 22 pairs of autosomes
– or, homologous chromosomes
• 1 pair of sex chromosomes
– XX female
– XY male
• Question: Why are there
pairs of chromosomes?
Where do the chromosomes
come from?
• We are originally one
cell:
• 23 of maternal origin
– ova carry these
• 23 of paternal origin
– sperm carry these
• If every cell has 46, how
do these end up with
only 23 and why?
Meiosis
Mitosis
• Cell Division
• Chromosomal
Replication
What does the genetic material
do?
• While the functions of the genetic material located on
the chromosomes are numerous and complicated, for
our purposes, we can examine the major function: that
of the synthesis of proteins.
• Proteins are a very large class of molecules that
perform a huge array of functions in living things. It
has been estimated that there may be as many as
50,000 different proteins in the human body, only
about 1500 of which have been identified.
• Proteins differ from one another, and thus perform
differently, based on their organization and makeup.
Proteins: What are they?
Basic: You are what you eat!
The ultimate source of
your body’s protein is
from your diet.
•
Functions include:
– Structure
– Transport
– Immune
•
Function reflects their
structure
–
Proteins have 3
dimensional structure
– Folded chains
Differentiation
• Unique proteins in different
cell types
• Keep in mind that every cell
receives a complete set of
chromosomes and thus the
genetic materials.
• Thus, although every cell
has the ability to produce
every single protein in the
body, specific cells only
“turn on” very small
segments of the total
genetic material and only
synthesize a very few
proteins.
Proteins: what distinguishes
one from another?
1. Proteins are composed of
chains of amino acids
(Polypeptide chains).
2. Polypeptide chains have
variable lengths.
3. The sequence of amino acids
along the chains vary.
4. Proteins can be made up of
one or, more usually, two or
more chains of amino acids.
5. Proteins have a folded three
dimensional structure
Amino Acids: What are they and where do
they come from?
Glycine (gly)
Glutamic acid
(glu)
Alanine (ala)
Aspartic acid
(asp)
Valine (val)
Isoleucine (Ile)
Leucine (leu)
Serine (ser)
Threonine (thr)
Proline (pro)
Lysine (lys)
Arginine (arg)
Glutamine (gln) Aspargine (asn)
Methionine (met) Cysteine (cys)
Tryptophan(trp) Tyrosine (tyr)
Histidine (his)
Phenylalanine
(phe)
• Chemical group
based on their
composition: an
“amine” and an
“acid”
• Of the 20 common
amino acids:
– 12 the body can
make
– 8 must be eaten
be obtained from
foods (these are
the essential
amino acids)
Proteins: How they are made:
amino acids
• Polypeptide chains=aa
• Sequence of aa crucial
to structure, and thus
function
• Sequence determined
by series of nucleic
acids and the genetic
code
• Determined by a gene
met valhisleuthraspalaglulys
val alaala
ss
cys
leu
trp
gly
lys
val
asn
ser
asp
glu
What is a gene?
• A “recipe” for a protein, or
more accurately, for a single
polypeptide chain.
• Located at a specific region
(locus) on a specific
chromosome.
• A gene can have many
alternative versions of itself.
These are known as alleles.
• Implications:
– different chromosomes carry
different information
– Alleles are one of the major
sources of variation.
Diversity of form and function
• The basis of evolution is variation
• This variability in biological form
and function arises from genetic
mutations, compounded by the
random assorting of genetic
materials during the production of
eggs and sperm.
• There are two levels in evolution :
1. Microevolution: the
generation by generation
changes in a population.
2. Macroevolution: the
evolution of populations over long
periods of time, usually resulting
in the appearance of a new
species.
The origins of Variation I
• Random changes in the structure of the
genetic material (DNA), which are called
mutations, result in the appearance of
new variations. This is one of the
crucial pieces of information that Darwin
lacked, and thus prevented him from
actually directly addressing the name of
his book: The Origin of Species (1859).
• It was an ongoing criticism of Darwinian
evolution until the discoveries of how
genetic material can randomly change
provided the missing data.
The origins of Variation II
• The second major source of variation is
the recombination of genetic traits that
results from the transmission of genetic
traits from male and female parents.
• During the process of producing sex
cells, the genetic material carried in the
chromosomes randomly assorts so that
each offspring receives a random
selection of parent’s genetic materials.
• Thus, each offspring confronts the
environment with a slightly different set
of genetic materials.
Genetics and Evolution
A Darwinian View
• Thus, genetic mechanisms produce
random changes (mutations) in the
genes. The changes are not in any way
dictated by the environment or the
needs of the animal.
• These mutations are acted upon by
natural selection via behavior.
• In time, the changes may come to
characterize the entire population.
Evolutionary Mechanisms
• Evolutionary Mechanisms effect the
frequency of genetic variations (alleles)
in a population, and thus represent the
way by which evolution operates.
• There are four evolutionary
mechanisms:
1. Mutation
2. Natural Selection
3. Gene Flow (Migration)
4. Stochastic Forces (random genetic
drift).
Evolutionary Mechanisms
1. Natural Selection:
reduces variation
2. Mutation:
increases variation
3. Gene Flow (Migration):
can reduce or increase variation
4. Stochastic Forces (Genetic Drift):
reduce variation
Action of Evolutionary Forces
• These evolutionary forces do not work
on individuals, but rather on
populations.
• Individuals do not evolve, and in
evolution, the only role played by
individual animals is to receive genetic
materials from parents and pass them
on to offspring.
• Evolution is differential reproduction,
and not necessarily survival .
Human Variation and Adaptation
• Human variation is very often related to the
evolutionary adaptation of a population to its
environment.
• But, it is important to keep in mind that mutations are
random events that do NOT appear as the result of
some need that a population has to adapt.
• As a result, variations are NOT adaptive all of the time
and in all places but are very much related to specific
environmental conditions. When conditions change, it
is often difficult for a species to modify to fit the new
environmental conditions and they will often become
extinct.
The Basis for Human Variation
• Finally in this context, it should be kept in mind that
there are variations that may not have an adaptive
basis. It is possible that in small populations,
variations have become part of the biology by random
changes in the genetic material. This process, known
as genetic drift, can result in the appearance of
features that are not part of an adaptive system.
These random, or stochastic (means random)
processes add a measure of uncertainty and
complexity to the study of human variation.
• For example, when a particular trait is examined (hair
color), should we always assume that the variations
are adaptive and look for an environmental cause?
Human Variation
There are all sorts of differences amongst
humans, and we are all aware that people
vary in facial and body features. We also
know that these differences extend to the
genetic materials themselves.
We will see from our examination of the human
fossil record that during our evolution,
humans became established in environments
with differing conditions.
Thus, the origins of many of our biological
variation appear to be directly related to our
evolution as a geographically diverse species
occupying a wide range of environments.
The Nature of Variation
Keep in mind the following:
• The similarity of humans across all populations is very
high, with numerous studies documenting that genetic
variability within major geographic areas (i.e. Africa or
Europe) is greater than the genetic variation between
geographic areas.
• All modern humans share the unique attributes of the
species, and thus are identical for this suite of features.
• What we can examine are those biological features, like
skin color, which do vary amongst geographical
populations, and which have often been used to
characterize ‘races’.
The study of human variability:
Description and process
• Populations vs individuals
• Nature vs nurture
• Stochastic vs adaptive
Variability in form and
function in adults is the
result of the interaction of
biocultural complexes
and reflects evolutionary
scenarios:
• Genetic
mechanisms
–
–
–
–
mutation
drift
selection
flow
• Development
• Environmental
variables
The Interaction of genes and
environment
In the development of an individual, a complex
interplay of the genetic materials and
environmental (which of course includes
culture) factors is responsible for the outcome:
a functioning (and reproducing) adult:
GENES
+
(Genotype)
interaction with ENVIRONMENT = ADULT Form
(Phenotype)
Adaptation: The interplay of
genotype and phenotype
• Genotype is the underlying framework
– Environment molds and channels genotype
into the final phenotype
– In humans, culture and the resultant
complex behavior are a unique basis for
the environment to influence and shape
final phenotype.
(This represents a complex interplay that
few other animals have.)
Adaptation
– Changes or modifications that enable a
person or group to survive in a given
environment
This can be accomplished by means of:
– Biological mechanisms
• Genetics
• Physiology
• Development
– Cultural, behavioral mechanisms
Environmental challenges
Human variation is related to
environmental variation, with many
biological complexes reacting to
variations such as:
• Disease
• Temperature
• Altitude
• Nutrition
Adaptation:
The basis of
body shape
and size?
Human
variability:
populations
vs individuals
The variable human species: Homo sapiens,
The product of evolution and adaptation