Bio112 Exam 3

How often do cells make ATP?

All the time!

What is the difference between cilia and flagella?

Cilia - usually has many, but shorter and they beat like oars. Can also be used for sensing what's going on outside cell Flagella, one or a few, longer, undulating motion that generates movement

What are some of the major functions of actin filaments?

Cytokinesis (final stage in cell division where cytoplasm is divided), cytoplasmic streaming (directed flow of cytosol and organelles, often seen in plant and fungal cells), cell crawling (seen in amoebae, slime molds, and certain animal cells).

Do organisms break down molecules other than glucose for energy? What are some of those molecules?

Yes! These molecules range from sucrose, maltose, and other simple sugars to large polymers such as glycogen and starch. Fats and proteins are also catabolized for energy!

What is the structure of an actin filament (Table 7.2)?

Two long strands coil around each other.

How many membranes do mitochondria have?

Two- the outer and inner membrane!

Do intermediate filaments have polarity?

Nope! They have identical ends and appear to serve only a structural role in eukaryotic cells.

Which enzyme catalyzes reaction 3 of glycolysis? Why is this reaction key?

Phosphofructokinase. This is the reaction key because before reaction 3, the sequence is not committed to glycolysis and glucose can be used in other pathways. After this step, you can't reverse the process.

What form is the carbon in when it enters the citric acid cycle? What form does it leave in (Fig. 9.10)?

Start: Citrate. End: Oxaloacetate. ^that was shown in the diagram other option: starts in acetyl coa, leaves as co2 (???)

What is homeostasis?

The conditions that the cell keeps its internal environment at no matter the environmental conditions.

How are the microtubules arranged in cilia and flagella in eukaryotic cells?

"9+2" arrangement of microtubules called the axoneme. 9 microtubule pairs (doublets) surround 2 central microtubules.

What are the high energy molecules produced by glycolysis? How many of each of them (net) are produced from one molecule of glucose?

2 NADH, 2 ATP, 2 pyruvate

Approximately how many ATP molecules are produced from each glucose molecule during aerobic respiration? How many of these molecules are produced from ATP synthase?

29 ATP molecules total from a glucose, not the theoretical 38. 25 ATP are produced by ATP synthase (the payoff stage)

Glucose has 6 carbons. Where are those carbons at the end of glycolysis (Fig. 9.5)?

3 in each pyruvate

What is the total potential energy difference from NADH to oxygen?

52 kcal/mol

What molecules are made in anabolic pathways from intermediates in cellular respiration?

? Intermediates in glycolysis can be used in synthesis of RNA and DNA, nucleotides are building blocks used in RNA and DNA synthesis. Acetyl CoA is the starting point for anabolic pathways that result in fatty acid synthesis, fatty acids can be used to build phospholipids and fats. In humans, about ½ the required amino acids can be synthesized from molecules siphoned from the citric acid cycle. If ATP is abundant, pyruvate can be used in the synthesis of glucose, excess glucose may be converted to glycogen or starch and absorbed.

What is a SRP?

A SRP is a Signal Recognition Particle- a complex of RNA and protein.

What is the cytoskeleton?

A dense and complex network of fibers that help maintain cell shape by providing structural support (NOT a static structure like bones)

What are the main differences between a dissecting microscope and a compound microscope in terms of their magnification abilities and types of specimens?

A dissecting microscope has less magnification (max of 20-40 times normal size), and works on live organisms. (Looks at organism in three dimensions) Compound microscopes have light pass through a specimen, usually capable of 400x magnification, and can see individual cells and large structures in cells. (Dead organisms typically.)

Explain how ATP can be both a substrate for and an inhibitor of the same enzyme (Fig. 9.7).

ATP can be at the active site or regulatory site, which changes how it affects the enzyme!

What is a fluorescence microscope used for?

A fluorescence microscope is used when one wants to see the location of specific proteins and stained the specimen with fluorescently tagged antibodies.

Where does the energy come from to power the movement of myosin along actin filaments (Fig. 7.23)?

ATP hydrolysis in the 'head' region of myosin causes the protein to attach to actin and change shape, the movement slides the myosin toward the plus end of actin.

What is a motor protein?

A protein that converts the chemical energy in ATP into the kinetic energy of mechanical work.

What is a pulse-chase assay?

A pulse-chase assay is made of two steps. 1. The "Pulse" (expose experimental cells to a high concentration of a modified amino acid for a short time.) 2. The "Chase" (end the pulse by washing the modified amino acid and replacing it with the normal version of the same molecule. The time following the end of the pulse is the chase. The proteins synthesized during the chase are NOT radiolabeled (pules ones are)

What are the three types of cytoskeletal elements found in eukaryotic cells? (Table 7.2)

Actin filaments, intermediate filaments, and microtubules.

When Racker studied mitochondria, what protein did he discover was made of stalks and knobs? What does this protein do?

ATP Synthase, which could both synthesize ATP and also hydrolyze it to form ADP and inorganic phosphate.

Does the citric acid cycle occur more or less when ATP levels are high? What about NADH?

ATP and NADH high = lower reaction rates. Better in scarcity.

What protein are actin filaments made of?

Actin

Which reactions (in Citric Acid Cycle) are regulated allosterically and which are regulated by competitive inhibition?

Allosteric regulation: 1 and 4 (by ATP). Competitive inhibition: 3, by NADH

What protein are microtubules made of?

Alpha tubulin and Beta tubulin, which exist as stable protein dimers

What is a facultative anaerobe?

An organism that can switch between fermentation and aerobic cellular respiration.

What is the electron transport chain (ETC)?

Any set of membrane-bound protein complexes and mobile electron carriers involved in a coordinated series of redox reactions. The energy from the redox reactions is used to actively transport protons from one side of a membrane to the other. [The molecules responsible for the oxidation of NADH and FADH2]

What happens to proteins as they move through the Golgi cisternae? Where do they go from there? (Fig. 7.21

As they move through the Golgi cisternae, proteins are sorted and sent to their intended destination. From there, the proteins go to different destinations, such as outside of the cell! (?)

Explain how high levels of ATP result in feedback inhibition of glycolysis at this step.

Because ATP serves as a substrate for the addition of a phosphate to fructose-6-phosphate (what reaction 3 produces), causing feedback inhibition.

Why do scientists think they evolved separately?

Because of the differences between their flagella.

Compare alcohol fermentation to lactic acid fermentation. Are lactic acid and alcohol fermentation the only two types of fermentation, or are there others?

Both create NAD+, but L.A. makes pyruvate while A.F. makes ethyl alcohol and carbon dioxide. No other types (?).

Compare and contrast aerobic respiration with anaerobic respiration: which aspects are the same and which are different? Which type of respiration is the most efficient?

Both produce ATP, but aerobic is more efficient. Aerobic respiration depends on oxygen, anaerobic respiration has a different electron acceptor.

Compare the burning of glucose to the controlled redox reactions that harness energy from the breakdown of glucose in the cell.

Burning = uncontrolled redox of glucose. Burning is less efficient, and less energy is storage.

Define catabolic and anabolic pathways

Catabolic pathways: sets of reactions that break down molecules. Anabolic pathways: sets of reactions that synthesize larger molecules from smaller components.

How do cells bring in large molecules? Where do they end up once inside? (???)

Cells bring in large molecules by being brought in through like...channel proteins. They end up in the lysosome/cytosol (????)

Which produces more ATP?

Cellular respiration

How is fermentation different from respiration in terms of the oxidation of glucose?

Cellular respiration results in the complete oxidation of the carbons in glucose to CO2 (like burning), while fermentation does not fully oxidize glucose. (Small, reduced organic molecules are produced as waste.)

Which is more efficient in terms of ATP production: glycolysis + fermentation or cellular respiration?

Cellular respiration! (2 ATP vs 29)

What is the difference between differential centrifugation and density-gradient centrifugation? See Figure B7.1.

DC focuses on size, density centrifugation focuses on density.

How do they enter into cellular respiration- at the same step as glucose or different steps (Fig. 9.3)?

Different steps based on molecules- look at figure above!!!

What is differential centrifugation used for?

Differential centrifugation is used to isolate specific cell components.

What is the motor protein that powers the movement of cilia and flagella in eukaryotic cells?

Dynein.

How many carbons enter and how many leave?

Each round starts with a 2-carbo acetyl molecule (acetyl CoA) and ends with the release of 2 CO2.

How are electron microscopes different from light microscopes?

Electron microscopes view cells at high magnification via electrons, while compound microscopes rely on light.

What are two of the most fundamental requirements of a cell?

Energy and carbon.

Why are steps 1-5 of glycolysis referred to as the energy-investment phase?

Energy is put into glycolysis.

Where is pyruvate dehydrogenase located in eukaryotes? In bacteria and archaea?

Eukaryotes: mitochondria, Bacteria & Archaea: cytosol

Where does the cycle take place in eukaryotes? In bacteria and archaea?

Eukaryotes: mitochondrial matrix, Bacteria & Archaea (Prokaryotes): Cytosol

How are eukaryotic flagella different from prokaryotic flagella?

Eukaryotic flagella: single microtubules constructed from tubulin dimers, move the cell by undulating (whip back and forth), surrounded by the plasma membrane. Prokaryotic flagella: single helical rod of flagellin [bacteria] or other types of proteins [archaea], move the cell by rotating, flagella are not surrounded by the plasma membrane.

What is exocytosis?

Exocytosis is when something is trapped in a transport vesicle and taken outside the plasma membrane to be secreted out. (like a trash bag)

What conditions stop pyruvate processing? Is feedback inhibition involved? Which molecules will promote pyruvate processing, and which will inhibit pyruvate processing?

Feedback inhibition stops pyruvate processing- too much NADH, acetyl COA, or ATP will cause incorrect phosphorylation of the enzymes. More ADP, pyruvate, CoA, or NAD+ encourages pyruvate processing.

Study Fig. 9.20. Does fermentation use the electron transport chain?

Fermentation doesn't use the ETC- it's the backup for it the ETC is shut down.

What is the function of fermentation?

Fermentation oxidizes NADH to regenerate NAD+.

What is the structure of an intermediate filament (Table 7.2)?

Fibers wound into thicker cables.

What is GFP? Why can it be used to visualize proteins in live cells?

GFP is green fluorescent protein, and it can be used to visualize proteins in live cells because it allows researchers to tag specific molecules or structures and follow their movement in live cells over time.

How does free energy change as electrons are passed through the ETC (Fig. 9.14)?

Free energy decreases to 0.

What happens to each of the molecules that leave?

Free energy goes down- NADH and FADH2 are used to turn O2 and H into water. (?)

What are the four steps involved in the complete oxidation of glucose during aerobic cellular respiration (Fig. 9.2).

Glycolysis -> Pyruvate Processing -> Citric Acid Cycle -> Electron Transport and Oxidative Phosphorylation.

Which 3 processes are involved in the complete oxidation of glucose (Fig. 9.12)? Which molecules enter and which molecules leave these processes?

Glycolysis, pyruvate processing, and the citric acid cycle. Glycolysis: Start with glucose, end with 2 pyruvate and 2 NADH and 2 ATP. Pyruvate processing: start with 2 pyruvate, end with 2 acetyl CoA and 2 CO2 and 2 NADH. Citric acid cycle: Start with 2 acetyl CoA, end with 4 CO2, 2 ATP, and 6 NADH and 2 FADH2

What is the structure of a microtubule?

Hollow tubes

Where in the cell does glycolysis occur?

In the cytosol/cytoplasm

Outline the steps of differential centrifugation

Low speed to medium to high speed. Gets more and more components to fall to the bottom, from largest to smallest.

Where are actin filaments found in the cell?

In animal cells, these filaments are particularly abundant just under the plasma membrane.

What Happens Inside the Golgi Apparatus?

In the Golgi apparatus, cargo enters one side and exits the other.

In eukaryotes, where does pyruvate get transported (which part of the cell)?

It is transported from the cytosol to mitochondria.

What are the two types of motor proteins that are able to bind to and move along microtubules? How are these motor proteins different?

Kinesin and dynein. Kinesin bring stuff out of Golgi, dynein brings stuff into Golgi

What types of proteins are intermediate filaments made of?

Keratins, larnins, or others!

Explain how lactic acid fermentation can regenerate NAD+.

Lactic acid fermentation regenerates NAD+ by reducing pyruvate to form lactate (a deprotonated form of lactic acid)

What is another name for actin filaments?

Microfilaments

What is a MTOC?

Microtubule-organizing center, where microtubules originate from. (It's a structure.)

What are some of the major functions of microtubules?

Microtubules provide stability and are involved in movement. They also provide a structural framework for organelles. Best known for their role in separating chromosomes during mitosis and meiosis.

Why are steps 6-10 of glycolysis referred to as the energy-payoff phase?

More energy is given off at the end. Net yield 2 NADH, 2 ATP, 2 pyruvate

What is the motor protein that is able to bind to and move along actin filaments?

Myosin

When researchers isolated different parts of mitochondria, which part did they find could oxidize NADH?

NADH is oxidized when combined with the inner membrane of the mitochondria, including the cristae. (In prokaryotes, the plasma membrane is required for oxidation!)

How many NADH, FADH2, and ATP are produced for each turn of the cycle? (of the citric acid cycle)

NADH: 3, FADH2: 1, ATP: 1 (or GTP, depending on the cell)

What is the nuclear localization signal?

NLS is the common sequence that proteins that get transported to the nucleus have.

Is each step of glycolysis catalyzed by an enzyme?

No (?)

What are the intermediate filaments found inside the nucleus?

Nuclear lamins

Describe the experiments on nucleoplasmin that led to the idea that proteins that function in the nucleus have a nuclear localization signal (NLS)? (Fig. 7.17).

Nucleoplasmin was injected into the cytoplasm of living cells, and the expected protein was found to be quickly concentrated inside the nucleus. Leads to understanding of NLS. (especially when proteases were used to cleave nucleoplasmin).

What are two techniques mentioned in this section used to study cells? What are some of their limitations?

One technique is differential centrifugation. This technique allowed researchers to isolate particular cell components and analyze their chemical composition, breaking apart cells and separating the parts. Unfortunately, this means dismantling the cell. This technique also cannot allow investigators to explore how things move from place to place in the cell nor how parts interact. The second technique is imaging- or simply looking at cells. By using light microscopes and electron microscopes, we are able to see cells in high resolution. Unfortunately, we can only see a fixed "snapshot" of the cell with an electron microscope.

What does reduced mean? What does oxidized mean?

Oxidation is loss of electron, reduction is gain of electron.

What molecule is the final electron acceptor at the end of the ETC?

Oxygen! (Allows for oxidative phosphorylation)

What type of cell did Palade and his team use to test their hypothesis about the secretory pathway? Why did they use these cells?

Palade and his team used pancreatic cells They used these cells because they are specialized for secreting digestive enzymes into the small intestine and are packed with rough ER and Golgi.

Cells of multicellular organism are made up of specialized cells for certain functions. Give examples of different types of cells found in plants and animals (Figure 7.15).

Pancreatic cells export digestive enzymes, testis cells export lipid-soluble signals, cardiac muscle cells use ATP to generate the heartbeat, leaf cells manufacture ATP and sugar. (first three are animal cells, leaf cell is a plant cell)

How do cells obtain glucose?

Photosynthetic organisms can produce glucose via photosynthesis and are eaten or decomposed by other organisms.

How do proteins get into the ER lumen or membrane?

Proteins get into the ER lumen or membrane because the translocon has molecular 'gates' that divert stretches of nonpolar amino acids in the growing protein into the phospholipid bilayer.

How do Proteins Reach Their Destinations?

Proteins reach their destination by moving through the Golgi.

How do proteins travel from the ER to the Golgi?

Proteins travel from the ER to the Golgi by going through the ER Golgi assembly line. (Shoutout to lysosomes)

What molecule is pyruvate oxidized to? What molecules go in, and what molecules come out of this reaction (Fig. 9.9)?

Pyruvate dehydrogenase couples the oxidation of one carbon in pyruvate to the reduction of NAD+, resulting in the release of a CO2 molecule and production of NADH. The same enzyme complex then takes the two-carbon acetyl unit (-COCH3) and covalently bonds it to a compound called coenzyme A (CoA), creating Acetyl CoA! [Pyruvate, NAD+, and CoA go in, CO2, NADH, and acetyl CoA come out.]

How is the pyruvate transported into the mitochondrial matrix?

Pyruvate moves from the cytosol across the mitochondrial outer membrane through small pores and is then transported into the matrix through a carrier protein in the inner membrane.

What reaction does pyruvate dehydrogenase catalyze?

Pyruvate! (?)

How did his (Racker's) experiments confirm that the stalks and knobs have the ability he hypothesized?

Racker and his researchers added the stalks and knobs back to vesicles that had been stripped of them, and confirmed the vesicles regained the ability to synthesize ATP.

Define redox potential. How does redox potential relate to the order in which electrons are passed between molecules in the ETC?

Redox potential is the ability to accept electrons in a redox reaction. Based on redox potential, it should be possible to arrange redox reactions into a logical sequence. The idea was that electrons would pass from a molecule with a lower redox potential to one with a higher redox potential, creating tighter bonds as they move through the chain.

What molecules can pass freely (diffuse) in and out of the nucleus through the nuclear pore complexes?

Small molecules, like nucleotides, can freely diffuse through nuclear pores into the nucleus along their concentration gradients. The import of larger molecules, such as proteins and RNA, is more selective.

How is chemiosmosis different from substrate-level phosphorylation?

Substrate-level phosphorylation is different from chemiosmosis because the former believes in the addition of organic phosphate (Pi) to ADP to form ATP, but chemiosmosis means formation of ATP via proton transfer (H+) depending on a concentration gradient.

Explain what we now know about the "knobs" and "stalks" that Racker first described (Fig. 9.18); how do they operate?

The "knob" component is called the F1 unit. The membrane-anchored, proton-transporting base component is the F0 unit. They are connected by a shaft and a stator, which hold the two units in place. The F0 unit spins as protons pass through, the shaft transmits the rotation to the F1 unit, causing it to make ATP from ADP and Pi.

How does the ER signal sequence direct ribosomes to the ER membrane?

The ER signal sequence directs ribosomes to the ER membrane by guiding the growing protein and associated ribosome to the rough ER.

How is the process of chemiosmosis similar to the generation of electricity from a hydroelectric dam?

The ETC pumps protons across the inner membrane, similar to the way a series of gigantic pumps force water up and behind a dam. When protons pass through the ATP synthase, it spins and releases energy used to synthesize ATP, which is analogous to how water passing through the turbines of hydroelectric dams causes them to spin and generate electricity.

Explain the relationships among centrosomes, centrioles, and MTOC?

The MTOC is in the centrosome, which is made of centrioles!

What are the other two names sometimes used for the citric acid cycle?

The TCA (tricarboxylic acid) Cycle or the Krebs Cycle.

What happens to glycolysis if NAD+ is not regenerated?

The cell will die.

What types of cells have intermediate filaments made up of keratins?

The cells that make up your skin and line surfaces inside your body contain about 20 types of keratin.

What is a proton-motive force?

The combined effect of a proton gradient and an electric potential gradient across a membrane, which can drive protons across the membrane.

What is the mitochondrial matrix? Draw a diagram of the membranes of the mitochondria and label the membranes and spaces (Fig. 9.8).

The compartment enclosed within the inner membrane. MAKE FLASHCARD OF TEST DIAGRAMS!!!

What's the difference between the cis and trans face?

The difference between the cis and trans face is cisternae constantly form at the cis face while the old cisternae break apart at the trans face.

Study the components of the ETC (Table 9.3). What is that energy used for by the ETC components (Fig. 9.15)?

The energy is used to drive the active transport of protons across the inner membrane from the matrix into the intermembrane space. NEED A FLASHCARD OR PIC OR SOMETHING

What modifications of proteins occur in the ER?

The modification of proteins that occur in the ER are: proteins fold into 3D shape, those that enter the ER lumen interact with enzymes that catalyze the addition of carbohydrate side chains.

What is the organelle that materials are delivered to first from the outside of the cell before being delivered to the lysosome?

The organelle that materials are delivered to first from the outside of the cell before being delivered to the lysosome is the Early Endosome (??)

Diagram the nuclear membrane showing that it is a double membrane with many nuclear pores. Do the pores extend across both membranes? What functions are carried out in the nucleus? What molecules have to move out of the nucleus and what molecules have to move into the nucleus? How do they get in and out of the nucleus?

The pores extend across both membranes, connecting the inside of the nucleus with the cytosol. DNA replication, RNA transcription, and ribosome subunit assembly occur in the nucleus. Nucleoside triphosphates enter the nucleus, as do a variety of proteins responsible for copying DNA, synthesizing RNA, or assembling ribosomes. LOOK TO NEXT PART FOR HOW THEY GET IN! [Diagram on word doc!]

What mystery did Hans Krebs solve? How does the idea of a cycle solve the problem?

The problem Krebs solved was 'How is it possible that carboxylic aid was being recovered, rather then being used up?' By suggesting that the reaction sequence was a circle rather than a linear process, it was understandable that the acid would return.

What are the results of their pulse-chase experiment (Fig. 7.19).

The results: It is revealed that proteins are trafficked through the secretory pathway in a highly organized and directed manner.

What is the signal hypothesis proposed by Blobel and colleagues (Fig.7.20)?

The signal hypothesis predicts that proteins bound for the endomembrane system have a molecular ip code that serves a similar role to the nuclear localization signal in nucleoplasmin.

Outline the steps of the secretory pathway? (Fig. 7.18).

The steps of the secretory pathway are as follows: 1. Protein enters ER while being synthesized by ribosome and is processed, carbohydrate group(s) are added. 2. Protein exits ER in vesicle, travels to cis face of Golgi apparatus. 3. Protein enters Golgi apparatus and is further modified. 4. Protein exits Golgi apparatus in a vesicle and moves to the plasma membrane. 5. Protein is secreted from cell.

What is the structure of the Golgi apparatus?

The structure of the Golgi apparatus is a stack of flattened compartments called cisternae

What does the term chemiosmosis refer to?

The use of a proton gradient to drive energy-requiring processes (i.e., ATP production)

What are three different pathways that take materials to the lysosome? Define them.

The three different pathways are receptor-mediated endocytosis, phagocytosis, and autophagy. Receptor-mediated endocytosis: particles outside the cell bind to receptors on the plasma membrane. Membrane then folds in and pinches off to form a vesicle, which drops the cargo off in the early endosome. Macromolecules Phagocytosis: brings smaller cell or food particle inside cell, forming a phagosome Autophagy: Encloses a damaged organelle within a membrane, forming an autophagosome that is delivered to the lysosome and digested.

What does it mean for an actin filament to have polarity?

The two distinct ends have polarity, plus and minus. (Due to actin protein asymmetricity.)

How did Hans and Edward Buchner's experiments demonstrate that metabolism could be studied outside of cells?

The yeast extract broke down the sucrose and produced alcohol, despite being outside of an intact organism.

How are actin filaments organized within the cell?

They are organized into long, parallel bundles or dense, crisscrossing networks in which actin filaments are linked to one another by other proteins. This helps to stiffen the cell and define its shape.

What is the main function of intermediate filaments?

They function like a flexible internal scaffolding to help secure the shape and stability of the cell.

What kind of signal is necessary to get proteins to the lysosome?

To get proteins to the lysosome, the following signal is needed: the correct zipcode like receptor signal

What did Mitchell hypothesize was the "real job" of the ETC?

To pump protons across the inner membrane of mitochondria from the matrix to the intermembrane space.

What is meant by the comparison between ATP and cash?

To withdraw chemical energy from the accounts to get 'cash', storage carbohydrates are first hydrolyzed into their glucose monomers, which are then used to produce ATP through cellular respiration or fermentation.

How does the process of cellular respiration interact with other catabolic and anabolic pathways (Fig. 9.3)?

WORD DOC- PUT ON A FLASHCARD!!!!

What is substrate-level phosphorylation (Fig. 9.6)?

When ATP is produced from enzymes catalyzing the transfer of a phosphate group from a phosphorylated substrate to ADP.

Explain how Q couples the electron transfer to the transport of protons across the membrane.

When Q accepts electrons from complex I or complex II, it picks up protons from the matrix side of the inner membrane. This reduced form of Q then diffuses through the inner membrane, where its electrons are used to reduce a component of complex III near the intermembrane space, and the protons are released.

Do microtubules have polarity?

Yes. Protofilaments always align in the same orientation- alpha-tubulins at the minus end, beta-tubulins at the plus end.

How is a transmission electron microscope different from a scanning electron microscope? How are specimens prepared for each?

one type allows researchers to examine very thin cross sections of cells at extremely high magnification (Transmission electron microscopy), the other offers a view of surfaces at somewhat lower magnification (scanning electron microscopy) Cells are prepared by first being "fixed" (treated with a chemical agent that stabilizes the cell's structure while disturbing them as little as possible). Then the researcher permeates the cell with an epoxy plastic to stiffen it, then cut the cells into extremely thin sections with a glass or diamond knife. Then the specimens are saturated with a metal- often lead.