BIO Exam 3

Photosynthesis is carried out in the

chloroplasts

Layers of leaves

1. Upper epidermis

2. Mesophyll (contains chloroplasts)

3. Lower epidermis

Light is a form of

electromagnetic energy

The electromagnetic spectrum is

the entire range of electromagnetic energy

Light travels in

waves

Wavelength

Distance between each crest

Light also behaves as

particles, called photons

Photons have

Energy

The amount of energy of photons is

inversely related to their wavelength

When light meets matter, it can be

reflected, transmitted, or absorbed

Light equals

Energy

If light is absorbed

photons can excite e-

Visible light spectrum

wavelengths that produce colors we can see (350-700 nanometers)

Color

The wavelength reflected or transmitted

Absorption spectrum

a graph plotting a pigment’s light absorption versus wavelength

Only 5% of light’s energy is converted to

chemical energy

Pigments are at the heart of

transforming light energy

Primary plant pigments

Chlorophyll A&B

Accessory pigments

pick up other wavelengths

Photosystem

Association of proteins holding a special pair of chlorophyll A molecules in a reaction center, surrounded by light harvesting complexes

Light harvesting complexes

Pigment molecules bound to proteins acting as a focusing antenna beaming energy toward reaction center

Light reactions are on the

thylakoid membrane in chloroplasts

First step of the light reaction

PSII absorbs light

PSII is also known as

P680

During the first step of the light reaction

Chlorophyll A absorbs light, passed e- to primary electron acceptor

Electrons come from

water (oxygen is produced)

Second step of the light reaction

Transport chain

During the second step of the light reaction

E- passed to ETC I, proteins pump H+ from stroma into thylakoids, e- passed to PSI

Third step of the light reaction

PSI

PSI is known as

PS700

During the third step of the light reaction

PSI accepts electrons from transport chain, PSI uses energy from the light to push e- to a higher energy level for use in next step

Fourth step of the light reaction

NADPH formation

During the fourth step of the light reaction

The electrons pass from PS1 to ferredoxin proteins and ETC 2, another enzyme brings about the reduction of NADP+ to NADPH

NADPH is found in the

stroma

Fifth step of the light reaction

Chemiosmosis

During the fifth step of the light reaction

H+ diffuse back to the stroma through ATP synthase this drives the phosphorylation of ADP to ATP

High concentration of H+ in the

thylakoid

Calvin cycle builds

sugar from smaller molecules by using ATP and the reducing power of NADPH

Calvin cycle is in the

stroma of the chloroplasts

Light induced pH changed in stroma activate

some enzymes

First step of the Calvin cycle

Carbon fixation

During the first step of the Calvin cycle

CO2 is added to 5 carbon RuBP and the resulting 6 carbon molecule splits into 2 3PG molecules

The first step of the Calvin cycle is catalyzed by

Rubisco

Rubisco is the

most abundant enzyme on earth

Second step of the Calvin cycle

Reduction

During the second step of the Calvin cycle

3PG is phosphorylated by ATP and reduced by NADPH to G3P, some G3P exits and will form glucose, the rest goes on to regenerate RuBP

Third step of the Calvin cycle

Regenerate RuBP

During the third step of the Calvin cycle

G3P is combined with other spare G3P to reform RuBP using ATP

It takes 3 turns of the cycle to form

1 G3P which can be exported to the cytosol to make glucose or kept in the chloroplast to form starch from glucose

To make 1 glucose molecule requires

6 turns of the cycle and a total of 18 ATP and 12 NADPH

Dehydration is a problem for

plants

Stomata close on hot days which

conserves water, but also limits photosynthesis

Stomata closing

reduces access to CO2 and O2 builds up

Photorespiration

O2 combines with RuBP which leads to the oxidation of RuBP producing 1 G3P and 1 2-carbon molecule which causes a 25% deduction in photosynthesis

C4 photosynthesis

Initially have the carbon in a 4 carbon chain

C4 plants

minimize water loss and photorespiration by fixing CO2 in mesophyll and then transporting it to bundle Sheath cells to undergo the Calvin cycle

C4 synthesis steps

1. Carbon fixation to form oxaloacetate

2. Oxaloacetate forms pyruvate and CO2

3. CO2 enters the Calvin cycle

CAM (crassulacean acid metabolism)

CO2 is initially fixed into oxaloacetate, just as in C4, but there is no physical separation between initial fixation and the Calvin cycle

Time is the barrier between

fixation and Calvin cycle

DNA

two polynucleotide strands connected by hydrogen bonds

DNA is made from

nucleotides

Nucleotides

sugar + phosphate + nitrogenous base

DNA sugar is

deoxyribose

DNA bonds

phosphodiester bonds

DNA strands are

antiparallel and complementary

Information of DNA is stored in the

order of paired nitrogenous bases (A-T, G-C)

Purines

Adenine and Guanine

Pyrimidines

Thymine and Cytosine

A-T

2 H bonds

G-C

3 H bonds

Nucleosome

made up of DNA wrapped around balls of protein

Chromatin

organized compacted nucleosomes

Chromosomes

Long pieces of DNA that contain many genes

DNA exists as

chromosomes inside the cell

DNA in prokaryotes

loop of DNA

DNA in eukaryotes

linear and supercoiled during division

Humans have

46 chromosomes in 23 identical pairs

Diploid

2 sets of chromosomes (2n)

Haploid

1 set of chromosomes (n)

Gene

a section of DNA that encodes for a protein

Alleles

Different forms of the same gene

Locus

A location along a chromosome

Gene families

Groups of closely related genes

Genome

The collection of DNA found across all chromosomes in any given organism

Genomes of prokaryotes are

smaller

1869 Johann Friedrich

Swiss chemist who separated cell nuclei and found acidic material, which he termed “nuclein”.

1920s-1940s Griffith and Avery

Experiments using Streptococcus suggested DNA was an information carrying molecule, but many scientists still thought that protein contained hereditary information

1952 Hershey and Chase

Demonstrate that DNA stored hereditary information by following radioactively labeled DNA injected into cells by viruses

1950s Chargaff publishes DNA composition study showing 2 rules

1. The amount of A=T and G=C

2. The ratio for G-C and A-T varies among species

1953 Rosalind Franklin

used x-ray diffraction to get pictures of oriented DNA fibers

1953 Watson and Crick

Built a detailed molecular model based on all information available to them

Semiconservative

New molecules have one old new strand of DNA

Conservative

Original molecules serve as a template only and remains intact

Dispersive

New molecules of DNA are a complete mix of old and new strands

1958 Meselson and Stahl

grew bacteria on two different food mediums containing different nitrogen isotopes, which showed DNA replicated in a semiconservative manener

DNA replication requires 3 things

1. Something to copy- the parental DNA molecule

2. Something to do the copying- Enzymes

3. Building blocks to make copy- the nucleotides

Nucleotides added to the elongating chain are really

deoxynucleoside triphosphates (DNTP)

Nucleosides contain

deoxyribose, nitrogenous base, and 3 phosphate groups

Nucleosides provids some of the energy needed for

polymerization

First step of DNA replication

Initiation- replication begins at the origin of replication