Transcript Standard 3: Cell Stucture

Supplemental Chapter Material
8.2, 8.3, 9.2 and 13.2
Standard 2: Cellular Structure
 B.2.1 – Describe features common to all cells that are
essential for growth and survival, and explain their
functions
 B.2.2 – Describe the structure of a cell membrane and
explain how it regulates the transport of materials into
and out of the cell and prevents harmful materials from
entering the cell.
 B.2.3 – Explain that most cells contain mitochondria, the
key sites of cellular respiration, where stored chemical
energy is converted into useable energy for the cell and
some cells, including many plant cells, contain
chloroplasts, the key sites of photosynthesis, where the
energy of light is captured for use in chemical work.
Standard 2: Cellular Structure
 B.2.4 – Explain that all cells contain ribosomes, the key
sites for protein synthesis, where genetic material is
decoded in order to form unique proteins.
 B.2.5 – Explain that cells use proteins to form structures,
including cilia and flagella, which allow them to carry
out specific functions, including movement, adhesion
and absorption.
 B.2.6 – Investigate a variety of different cell types and
relate the proportion of different organelles within
theses cells to their functions.
Chloroplasts pp. 231 and 233
Photosynthesis takes place inside organelles called
chloroplasts.
 Chloroplasts contain saclike photosynthetic
membranes called thylakoids, which are
interconnected and arranged in stacks known as
grana.

Chloroplasts

Pigments are located in the thylakoid membranes.

The fluid portion outside of the thylakoids is known
as the stroma.
Energy Collection pp. 235-237
Because light is a form of energy, any compound
that absorbs light absorbs energy. Chlorophyll absorbs
visible light especially well.
 When chlorophyll absorbs light, a large fraction of
the light energy is transferred to electrons. These highenergy electrons make photosynthesis work.

THINK ABOUT IT

Why do chloroplasts contain so many membranes?

When most pigments absorb light, they eventually lose most of that
energy as heat. Chloroplasts avoid such losses. Membranes are the
key to capturing light energy in the form of high-energy electrons.
The Light-Dependent Reactions:
Generating ATP and NADPH

Thylakoids contain clusters of chlorophyll and proteins known as
photosystems.

Photosystems absorb sunlight and generate high-energy electrons that
are then passed to a series of electron carriers embedded in the thylakoid
membrane.
Energy Totals pp. 256-259

In the presence of oxygen,
the complete breakdown of
glucose through cellular
respiration results in the
production of 36 ATP molecules.

This represents about 36
percent of the total energy of
glucose. The remaining 64
percent is released as heat.
Steps in Translation pp. 368-370

Messenger RNA is transcribed in the nucleus and
then enters the cytoplasm for translation.
Steps in Translation

Translation begins when a
ribosome attaches to an
mRNA molecule in the
cytoplasm.

As the ribosome reads
each codon of mRNA, it
directs tRNA to bring the
specified amino acid into the
ribosome.

One at a time, the
ribosome then attaches each
amino acid to the growing
chain.
Steps in Translation

Each tRNA molecule carries
just one kind of amino acid.

In addition, each tRNA
molecule has three unpaired
bases, collectively called the
anticodon—which is
complementary to one mRNA
codon.

The tRNA molecule for
methionine has the anticodon
UAC, which pairs with the
methionine codon, AUG.
Steps in Translation

The ribosome has a
second binding site for a
tRNA molecule for the
next codon.

If that next codon is
UUC, a tRNA molecule
with an AAG anticodon
brings the amino acid
phenylalanine into the
ribosome.
Steps in Translation

The ribosome helps
form a peptide bond
between the first and
second amino acids—
methionine and
phenylalanine.

At the same time, the
bond holding the first
tRNA molecule to its
amino acid is broken.
Steps in Translation

That tRNA then
moves into a third
binding site, from which
it exits the ribosome.

The ribosome then
moves to the third
codon, where tRNA
brings it the amino acid
specified by the third
codon.
Steps in Translation

The polypeptide chain
continues to grow until
the ribosome reaches a
“stop” codon on the
mRNA molecule.

When the ribosome
reaches a stop codon, it
releases both the newly
formed polypeptide and
the mRNA molecule,
completing the process
of translation.