Transcript The Living Cell - Carnegie Institution for Science

The Living Cell
Lecture 11
UNIV301 – Great Ideas of Science
Great Idea: Life is based on chemistry,
and chemistry takes place in cells
Cells
 All living things are made of cells, which
are like chemical factories
 Every cell has an “inside” and an outside,
separated by a cell membrane
 Every cell uses raw materials and energy to
produce new chemicals
 Every cell must contain information on how
to operate and how to make new cells
Observing Cells:
The Microscope
Observing Cells:
The Microscope
The Cell Theory
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Robert Hooke (1635-1702)
Cells are like small compartments
Matthais Scheiden – plants, 1838
Theodor Schwann – animals, 1839
The Cell Theory, 1839
 All living things are composed of cells
 The cell is the fundamental unit of life
 All cells arise from previous cells
Two Kinds of Cells
 Prokaryotes (“before nucleus”)
 Eukaryotes (“true nucleus”)
Cellular Architecture
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Organelle: Any specialized cell structure
Cell membrane (cell wall in plants)
Nucleus
Mitochondria and chloroplasts (power plants)
Plant Cells
Animal Cells
Lipids
Cell Membranes
 Cell Membranes
 Isolate the cell
 Separate cell parts
 Transport
 Individual molecules
 Channels for specific
materials
 Receptors
 Bind molecules
 Encapsulate
 Cell Wall (plants)
The Nucleus
 Nucleus
Nucleus
 Contains DNA
 Prokaryotes
 No nucleus
 Eukaryotes
 Nucleus
 The nucleus has a double membrane.
Why?
Cytoskeleton
 Cytoskeleton
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Gives cell shape
Anchors
Allows movement
Transport system
within cell
 Structure
 Strong filaments
 Complex web
How Is Energy Obtained?
Plants – make sugar in the presence of the
Sun by the process of photosynthesis
Energy (light) + CO2 + H2O  Glucose + O2
Carbohydrates (sugars)
Carbon
Hydrogen
Oxygen
Cellulose and Starch
How Is Energy Obtained?
Plants and animals convert sugar
into small energy-rich molecules
by the process of glycolysis.
Glucose  2 Pyruvic Acids + ATP
ATP  ADP + PO4 + energy
ATP: The Cell’s Energy
Currency
 Adenosine triphosphate (ATP)
 Provides energy
 Structure
 3 phosphate groups
 Sugar molecule: ribose
 adenine
 Function
 Removal of phosphate group provides energy
How Is Energy Obtained?
Some animals obtain
energy by the process of
respiration:
Glucose + O2 
Energy + CO2 + H2O
The Final Stages of Respiration
 Glucose is broken down
 CO2 is produced
 ATP is produced to serve as
energy-carrying molecules
 Result: 36-38 ATP
How Is Energy Obtained?
Many organisms obtain
additional energy from
pyruvic acid by the
process of fermentation:
Pyruvic Acid 
small molecules + ATP
Vinegar, alcohol, carbonic acid
The Energy Organelles:
Chloroplasts and
Mitochondria
 Chloroplasts
 Plant cells only
 Energy transformation
 chlorophyll
 Double membrane
 Mitochondria
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Plants and Animals
Produces the cell’s ATP
Double membrane
Has its own DNA
Mitochondria
Where ATP is manufactured
Mitochondria (mtDNA) = maternally inherited
Unaltered from your mother
Genetic material from common ancestor
Genetic anthropology
Genetics: The Genetic Code
 KEY IDEA: All living things share the
same genetic code
 Classical genetics – the observation
of organisms
 Cellular genetics – the observation of
cell division and chromosomes
 Molecular genetics – the study of DNA
and RNA
Two great mysteries of life
1. Like begets like
2. You begin life as a single cell
Three Stages
of Genetics Research
1. Classical Genetics
2. Cellular Genetics
3. Molecular Genetics
Gregor Mendel (1822-1884)
 Pea plant – breeding experiments
 Two-characteristic variations
 Established pure-breeding stocks
 Studied cross breeding
 Offspring’s traits are derived
from parents
Classical Genetics
 Gregor Mendel’s Laws
 Pea plant experiments
 Purebred
 Hybrid
 Results
 First generation all hybrid tall
If you cross a pure bred tall pea plant
with a pure bred short pea plant, all
offspring are tall.
T
T
t
tT
tT
t
tT
tT
Classical Genetics
 Gregor Mendel’s Laws
 Pea plant experiments
 Purebred
 Hybrid
 Results
 First generation all hybrid tall.
 Cross breed those hybrids.
 Second generation is ¾ tall
and ¼ short!
If you cross two hybrid pea plants,
¾ will be tall and ¼ will be short.
T
t
T
TT
Tt
t
tT
tt
Classical Genetics
Mendel Laws
1.Genes exist (“atoms of inheritance”)
2.Each parent contributes half.
3.Some are dominant and some are
recessive.
If you cross a pure bred tall pea plant
with a hybrid pea plant, what would the
first generation of offspring look like?
T
T
T
TT
TT
t
tT
tT
Gregor Mendel’s
Three Laws of Heredity
1. There exist “atoms of inheritance”
or genes
2. Each parent contributes half
3. Some genes are dominant, others
are recessive
4. Genes are expressed independently
of each other (WRONG)
Cellular Genetics
 Use microscope to observe cells dividing
 Chromosomes – elongated colored objects
Cellular Genetics
 Use microscope to observe cells dividing
 Chromosomes – elongated colored object
 Mitosis (one cell becomes two)
 Most cellular division in your body
 Humans 23 pairs (before division 46 pairs)
 2 daughter cells same as parent
 Meiosis (one becomes 4 gametes)
 Crossing-Over (reshuffle = end of meiosis)
 Recombination yields different mix of genes
Mitosis
 Mitosis is cell division
(Not sexual reproduction)
 Observe chromosomes
 Multi-step Process
1. Copy chromosomes
2. Spindle fibers
3. Migration of chromosomes
4. Nuclear membrane reforms
Mitosis
Meiosis
Meiosis is sexual reproduction
1 cell forms 4 gametes
Gametes are genetically unique
Multi-step process
1. Copy chromosomes
2. Crossing over
Meiosis
Meiosis is sexual reproduction
1 cell forms 4 gametes
Gametes are genetically unique
Multi-step process
1. Copy chromosomes
2. Crossing over
3. Segregation
4. Segregation again
Result: 4 daughter cells, each
with ½ normal number of
chromosomes. Each
chromosome is unique!
Molecular Genetics
 What chemical carries the genetic
message?
 How is that molecular message
translated into the chemicals of
life?
The Discovery of DNA
Oswald Avery (1877-1955)
DNA is composed of deoxyribose (5carbon sugar), phosphate, and one of
four bases (ATGC).
A = T; G = C
Sugar=Phosphate=Base (1:1:1 ratio)
Nucleotides: The Building
Blocks of Nucleic Acids
Nucleotides are made
of three molecules
1. Sugar
DNA: deoxyribose
RNA: ribose
2. Phosphate ion
3. Base
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
DNA’s Double Helix
Nucleotide:
Building blocks in
nucleic acids
(A phosphate linked to
a sugar linked to a
base)
DNA Structure
 Join nucleotides by
alternating phosphate
and sugar
 DNA
 2 strands of nucleotides
 Joined by base pairs
 Bonding pattern
 Adenine:Thymine
 Cytosine:Guanine
DNA Base Pairing
Adenine:Thymine
Cytosine:Guanine
The Replication of DNA
DNA replication occurs
before mitosis & meiosis
Process
1. DNA double helix splits
2. New bases bond to
exposed bases
3. Results in two identical
DNA strands
Proteins – Enzymes
Amino Acids
 Amino group
 Carboxyl group
 Side-group (20
different things)
Protein – sequence of
amino acids
 Primary – chain of
amino acids
 Secondary – folding of
chain
 Tertiary
 Quaternary
How Does DNA Make Protein?
1. Chromosomes (DNA) carry the
genetic message
2. Messenger RNA copies the genetic
message
3. Transfer RNA holds an amino acid
4. Ribosomal RNA assembles a protein
RNA Structure
1. Single strand of
nucleotides
2. The sugar is ribose
3. Thymine is replaced
by uracil (U), which
bonds with adenine
DNA to Proteins
 Protein pulls apart DNA
 Make one Messenger RNA (mRNA)
 Single stranded molecule carries one gene
 64 combinations of bases
 Codons (3 DNA letters) copied to mRNA
 Transfer RNA (tRNA)
 Codon at top matches to mRNA codon
 Associated Amino Acid attached
 Ribosomes
 Machine that makes proteins
 Two units (small & large) – reads mRNA
 Attaches amino acids from tRNA (creates a protein)
From DNA to Protein
1.
2.
3.
4.
Transcription: Use DNA to make mRNA
Attach mRNA to ribosome
Translation: RNA to amino acids
Fold amino acids into protein