Prokaryotes and Viruses( 원핵생물과 바이러스 )

Chapter 25

보툴린 독소 ( 상품명 : 보톡스 ) 를 생산하는 Clostridium 속의 세균 중의 하나인 Clostridium butyricum.

Prokaryotes: The smallest organisms

그림 25.1. 바늘 끝의 막대기형 세균 . (a) 70 배 , (b) 350 배 , (c) 14,000 배 확대 .

25.1 Prokaryotic Structure and Function

Prokaryotes are simple in structure compared with eukaryotic cells

Prokaryotes have the greatest metabolic diversity of all living organisms

Prokaryotes differ in whether oxygen can be used in their metabolism

25.1 (cont.)

Prokaryotes fix and metabolize nitrogen

Prokaryotes reproduce asexually or, rarely, by a form of sexual reproduction

In nature, bacteria may live in communities attached to a surface

Prokaryotes

Colonize a great diversity of habitats

Are small but complex cells

Have great metabolic diversity

Adapt rapidly to their environments

Three Common Shapes in Prokaryotes Spherical: cocci( 구균 ) Rodlike: bacilli( 간균 ; 막대형 ) Spiral: vibrios (curved)( 콤마형 ) and spirilla (helix)( 나선형 )

그림 25.2. 원핵생물의 일반적인 모양 . (a) 구균인 Micrococcus, (b) 막대모양의 Salmonella, (c) 나선형인 Spiroplasma 의 SEM 촬영 .

Prokaryotic Genomes

Prokaryotic chromosome• Single, circular DNA molecule

• Packaged into nucleoid( 핵양체 )•No nucleolus•No nuclear membranes

Plasmids• Small circles of DNA

• Genes supplement nucleoid genes

• Replicate independently (along with main DNA)

그림 25.3. 세균 세포의 구조 .

Prokaryotic Ribosomes

Bacterial ribosomes• Smaller than eukaryotic ribosomes

• Protein synthesis similar to eukaryotes

Archaeal ribosomes• Size similar to bacteria

• Different structure

• Protein synthesis is combination of bacterial and eukaryotic processes

Prokaryotic Cell Wall

Protects plasma membrane• Helps withstand osmotic pressure

• Prevents action of detergent-like chemicals

Made of peptidoglycans• Polysaccharide polymers connected by short

polypeptides

Gram Stain

Gram stain technique(1882 년 네덜란드 Gram)• Stain with crystal violet, then with iodine

•Fixes dye to cell wall• Wash with alcohol• Stain again with fuchsin( 퓨신 ) or safranin (사프라닌 )

Gram-positive bacteria• Appear purple because crystal violet retained

Gram-negative bacteria• Appear pink because crystal violet lost

그림 25.4. 그람양성과 그람음성 세균의 세포벽 구조 . (a) 그량양성 세균의 두꺼운 세포벽 , (b) 그람음성 세균의 얇은 세포벽 .

Slime Coat( 점액질 껍질 )

Capsule( 협막 )• Slime attached to cells

Slime layer( 점액층 )• Loosely associated with cells

Protects bacteria from desiccation, antibiotics, viruses, antibodies, and enzymes

Helps bacteria adhere to surfaces

그림 25.5. 그람음성 세균인 Rhizobium 의 세포벽을 둘러싼 협막 .

Flagella( 편모 )

그림 25.6. 그람음성 세균의 편모 . 양성자 (H+) 기울기가 시계반대 방향으로 편모를 회전시키는 모터를 구동한다 .

Protein fibers rotate like propellers

Pili ( 섬모 )

Rigid protein shafts ( 자루 , 손잡이 ) extend from cell walls

Mostly in Gram-negative bacteria

Help bacteria attach to each other or to surfaces

그림 25.7. 분열 중인 대장균 (E. coli) 의 표면에 돌출된 선모 .

Obtaining Carbon and Energy (1)

Autotrophs (auto = self; troph = nourishment) ( 독립영양생물 ) • Use carbon dioxide as their carbon source

Heterotrophs( 종속영양생물 )• Obtain carbon from organic molecules

Obtaining Carbon and Energy (2)

Chemotrophs( 화학영양생물 )• Obtain energy by oxidizing inorganic or organic

substances

Phototrophs( 광영양생물 )• Use light as energy source

Chemoautotrophs( 화학독립영양생물 )

Obtain energy by oxidizing inorganic substances• Hydrogen, iron, sulfur, ammonia, nitrites, nitrates

• Use electrons from oxidation to reduce CO2 or for ATP synthesis

Use CO2 as carbon source

Common lifestyle for many bacteria and most archaeans, but not found in eukaryotes

Chemoheterotrophs( 화학종속영양생물 )

Obtain energy by oxidizing organic substances

Obtain carbon from organic substances

Prokaryotic group with largest number of species • Many responsible for decomposing matter

• Many cause diseases in humans, domesticated animals, and plants

Photoautotrophs( 광독립영양생물 ) Use light as energy source

Use CO2 as carbon source

Cyanobacteria( 남세균 )• Use water (H2O) as electron source for reducing

CO2

Green sulfur bacteria( 녹색황세균 ) and purple sulfur bacteria( 홍색황세균 )• Use sulfur or sulfur compounds (H2S) as source

of electrons for reducing CO2

Photoheterotrophs( 광종속영양생물 )

Use light as ultimate energy source

Obtain carbon from organic substances rather than CO2

Green and purple nonsulfur bacteria (녹색비황세균 ; 홍색비황세균 )• Unable to oxidize sulfur or other inorganic

substances as source of electrons for reductions

• Use other substrates: H2, alcohols, or organic acids

그림 25.8. 생물의 영양 방식 .

Prokaryotes and Oxygen: Aerobes

Aerobes( 호기성 생물 , 산소성 생물 )• Require oxygen for cellular respiration

• Oxygen is the final electron acceptor

Obligate aerobes( 절대호기성 생물 )• Cannot grow without oxygen

Prokaryotes and Oxygen: Anaerobes

Anaerobes( 혐기성 생물 , 무산소성 생물 )• Do not require oxygen to live

Obligate anaerobes (poisoned by oxygen)• Use fermentation or type of respiration in which

inorganic molecules (NO3– or SO4

2–) are final electron acceptors

Facultative anaerobes( 조건 혐기성 생물 )• Use O2 when present• Use fermentation under anaerobic conditions

Prokaryotes and Nitrogen (1)

Nitrogen fixation( 질소고정 )• Conversion of atmospheric nitrogen (N3) to

ammonia (NH3)

• Ammonia ionized to ammonium (NH4+) for

biosynthesis

Nitrogen-fixing bacteria include• Some cyanobacteria

• Free-living Azotobacter

• Bacteria such as Rhizobium that are symbiotic with plants

Prokaryotes and Nitrogen (2)

Nitrification[ 질 ( 산 ) 화작용 ]• Conversion of ammonium (NH4

+) to nitrate

(NO3–)( 질산 )

• Two-step conversion by nitrifying bacteria•Some types of bacteria convert ammonia to nitrite

(NO2–)( 아질산 )

•Other types convert nitrite to nitrate

Prokaryote Reproduction( 생식 )

Binary fission( 이분법 )• Asexual reproduction

• Produces exact copies of parent

Conjugation( 접합 )(17 장에서 설명 )• Two cells connected by pilus

• Part of DNA of one cell is transferred to another cell (usually plasmids)

Endospore( 내생포자 )

Develops inside some bacteria when environmental conditions are unfavorable

Metabolically inactive

Highly resistant to heat, desiccation, attack by enzymes or chemicals

그림 25.9. 파상풍을 일으키는 위험한 병원 세균인 Clostridium tetani 의 발달 중인 내생포자 .

Biofilms( 생물막 )

Complex aggregation of prokaryotes attached to a surface, forming a community

Detrimental consequences• Harmful when attached to surgical equipment and

supplies or certain tissues in the body

• 1000 times more resistant to antibiotics than bacteria in liquid culture

Beneficial consequences• Used in sewage treatment plants( 오물처리시설 )

• Help in cleanup of toxic organic molecules in groundwater (bioremediation)[ 생물 ( 적 ) 정화 ]

Biofilms

Complex aggregation of prokaryotes attached to a surface, forming a community

그림 25.10. 생물막의 형성단계 .

25.2 Domain Bacteria( 진정세균 영역 )

Molecular studies reveal more than a dozen evolutionary branches in the Bacteria

Bacteria cause diseases by several mechanisms

Pathogenic bacteria commonly develop resistance to antibiotics

Classification of Prokaryotes

그림 25.11. 원핵생물의 간략한 계통수 .

생물

Bacteria

12 separate evolutionary branches

Six most important groups:• Proteobacteria

• Green bacteria

• Cyanobacteria

• Gram-positive

• Spirochetes

• Chlamydias

The Proteobacteria( 프로테오박테리아 )(1)

Gram-negative bacteria• Purple sulfur (photoautotrophic)

• Purple nonsulfur (photoheterotrophic)

• Purple photosynthetic pigment

Free-living proteobacteria (chemoheterotrophs)• Some cause human diseases

•Bubonic plague( 림프선페스트 ), Legionnaire’s diseas ( 레지오넬라병 ), gonorrhea( 임질 ), gastroenteritis( 위장염 ), dysentery( 이질 )

• Some plant pathogens•Rot( 썩음 병 ), scabs( 무름병 ), wilts( 시들음병 )

The Proteobacteria (2)

Myxobacteria (chemoheterotrophs)• Form colonies held

together by slime• Secrete enzymes to

digest other bacteria• When conditions

unfavorable, form fruiting bodies that disperse spores to form new colonies

그림 25.12. 점액세균인 Chondromyces crocatus 의 자실체 .

The Green Bacteria( 녹색세균 )

Gram-negative photosynthetic bacteria • Sulfur bacteria (photoautotrophic), usually in hot

springs

• Nonsulfur bacteria (photoheterotrophic), usually in marine and high-salt environments

Distinctive chlorophyll compared to plants

Do not release oxygen as byproduct of photosynthesis

The Cyanobacteria( 남세균 )

Gram-negative photoautotrophs

Blue-green color

Photosynthesis similar to plants

Release oxygen as byproduct of photosynthesis

그림 25.13. 남세균 . (a) 연못의 표면을 덮고 있는 남세균의 군락 . (b) 와 (c) 연쇄상의 남세균 세포 . 이질세포 (heterocyst)는 질소를 고정하는 특수화된 세포이다 .

The Gram-Positive Bacteria (1)

Primarily chemoheterotrophs Many pathogenic species

• Anthrax( 탄저병 )• Staphylococcus

•Food poisoning, skin infections, toxic shock syndrome, pneumonia

( 페렴 ), meningitis ( 수막염 )

• Streptococcus•Strep throat( 급성인후염 ),

pneumonia, scarlet fever (성홍열 ), kidney infections

그림 25.14. 긴 세포 사슬을 형성하는 Streptococcus.

The Gram-Positive Bacteria (2)

Some beneficial species• Lactobacillus

•Lactic acid fermentation( 유산균 발효 ) used to produce pickles, sauerkraut( 양배추 절임 ), yogurt

Mycoplasmas• Naked cells that have lost their cell walls

• Smallest known cells (0.1 to 0.2 µm in diameter)

The Spirochetes( 나선균 ) Gram-negative spiral-shaped bacteria

• Propelled by rotation of flagella

• Enables movement in thick mud and sewage

Beneficial or harmless species• Spirochetes in termite intestine( 흰개미 내장 )

digest plant fiber

• Treponema in mouth

Pathogenic species• Syphilis( 매독 ), relapsing fever( 열대 회귀열 ),

Lyme disease( 라임병 )

The Chlamydias( 클라미디아 )

Gram-negative bacteria• Cell walls with membrane outside

• Lack peptidoglycans

Intracellular parasites that cause diseases in animals

그림 25.15. 인간 세포의 내부에 있는 Chlamydia trachomatis 세포

Bacterial Disease Mechanisms

Exotoxins( 외독소 )( 독성 단백질 )• Toxic proteins leaked or secreted

•Clostridium botulinum (botulism exotoxin)( 보톡스 )

Endotoxins( 내독소 )( 외막의 지질다당류 )• Toxins only released when bacteria die or lyse

•E. coli, Salmonella, Shigella

Exoenzymes( 외효소 )• Enzymes secreted that digest plasma membrane

•Streptococcus, Staphylococcus, Clostridium

Resistance to Antibiotics

Pathogenic bacteria may develop resistance to antibiotics• Mutation of their own genes

• Acquiring resistance genes from other bacteria

Resistant strains difficult to treat with conventional antibiotics

Resistance is a form of evolutionary adaptation

25.3 Domain Archaea( 고세균 영역 )

Archaea have some unique characteristics

Molecular studies reveal three evolutionary branches in the Archaea

The Archaea

Archaea are more closely related to domain Eukarya than domain Bacteria

Characteristics• Some features like bacteria

• Some features like eukaryotes

• Some unique features

Unique Characteristics

Extremophiles( 극한 생물 )• Archaea found in extreme

environments such as hot springs, hydrothermal vents ( 열수구 ), salt lakes

그림 25.16. 대표적인 고세균 서식지 . (a) 유타주 Great Salt Lake 의 고농도 염수 . 적자색을 띤다 . (b) 고온의 황이 풍부한 Yellowstone 국립공원의 에메랄드 풀 . 밝은 색을 띤다 .

Archaean Unique Characteristics

Plasma membrane• Contains unusual lipid molecules

• Makes them more resistant to extremes

Cell walls• Some distinct molecules similar to peptidoglycans

• Some made with proteins or polysaccharides

• Resistant to physical disruption

The Euryarchaeota( 유리 고세균문 )(1)

Methanogens( 메탄생성균 )• Live in reducing environments

• Obligate anaerobes in•Anoxic sediments( 산소결핍 침전물 ) of swamps

( 늪 ), lakes, marshes( 습지 )•Rumen( 반추동물의 위 ) of cattle( 소類 ), sheep,

camels•Large intestine of humans and dogs•Hindguts( 후장 ) of insects

The Euryarchaeota (2)

Halophiles( 호염성 세균 )• Live in highly saline (salty) environments

• Aerobic chemoheterotrophs•Obtain energy from sugars, alcohols, amino acids•Some use light as a secondary energy source

The Euryarchaeota (3)

Extreme thermophiles( 극호열성 세균 )• Live in extremely hot environments

•Hydrothermal vents, hot springs•70°C to 95°C

• Obligate or facultative anaerobes

The Crenarchaeota( 크렌 고세균문 )

Extreme thermophiles( 극호열성 세균 )• 75°C to 105°C

Psychrophiles (“cold loving”)( 호냉성 세균 )• –10°C to –20°C

• Antarctic and Arctic oceans( 남극과 북극의 해양 )

Mesophiles( 중온성 세균 )• Many plankton in cool, marine waters

The Korarchaeota( 코르 고세균문 )

Oldest lineage in Archaea• Recognized only by sequences in DNA samples

• Found in hydrothermal environments but have never been isolated and cultivated in lab

• Nothing known about their physiology

25.4 Viruses, Viroids, and Prions

Viral structure is reduced to the minimum necessary to transmit nucleic acid molecules from one host cell to another

Viruses infect bacterial, animal, and plant cells by similar pathways

25.4 (cont.)

Viral infections are typically difficult to treat

Viruses may have evolved from fragments of cellular DNA or RNA

Viroids and prions are infective agents even simpler in structure than viruses

Viruses

Nonliving infective agents( 무생물 감염체 )• No metabolic system of their own

• Have minor to major effects on most organisms

Virus particle (virion) consists of a nucleic acid genome enclosed in a protein coat (capsid)

Bacteriophages commonly infect bacteria

Viral Structure

Viral genome• DNA or RNA

• Double-stranded or single-stranded

• Few genes to 100 or more

Viral coat• Made of a single type of protein or up to 50

different proteins

• Includes recognition proteins that bind to host cell

Helical Viruses( 나선형 바이러스 )

Protein subunits assemble in rodlike spiral around the genome

Common form of plant viruses

Polyhedral Viruses( 다면체형 바이러스 )

Proteins form triangular units, fit together like a geodesic sphere (측지선적인 구형 )

Infect plants, animals, bacteria

Some have protein spikes for host cell recognition

Enveloped Viruses( 피막 바이러스 )

Helical or polyhedral virus covered by surface membrane derived from host cell

Protein spikes extend through membrane for host cell recognition and adhesion

Complex Polyhedral Viruses( 복합 다면체형 바이러스 )

Polyhedral head plus complex tail

Genome in head, injected into host cell through the sheath

( 나선껍질 )

Infection of Bacteria: Lytic Cycle( 용균 회로 ) (1)

Phage attaches to host cell

Lysozyme digests hole in cell wall

Phage DNA enters bacterium

Infection of Bacteria: Lytic Cycle (2)

Phage genes expressed to direct phage replication• Phage proteins synthesized

• Phage DNA replicated

• Assembly of progeny phage particles

Lysozyme lyses the host to release the progeny

Infection of Bacteria: Lysogenic Cycle( 용원 회로 ) (1)

Lytic cycle starts but viral DNA inserts into host cell DNA

Production of new viral particles delayed

Integrated viral DNA (prophage)( 프로파지 ) remains inactive, but is replicated during cell division

Infection of Bacteria: Lysogenic Cycle (2)

Certain environmental signals trigger the prophage to loop out of chromosome

Lytic cycle resumes

Infection of Animals: Unenveloped Viruses( 무피막 바이러스 )

Virus binds to host using recognition proteins• Examples: adenovirus and poliovirus

Whole virus taken into host by endocytosis

Virus directs synthesis of new viruses like in bacteria, kills host when cell ruptured

Infection of Animals: Enveloped Viruses( 피막 바이러스 )

Virus binds to host using recognition proteins• Examples: herpes, pox, HIV, influenza

Whole virus taken into host• Fusion of envelope with plasma membrane

Virus directs synthesis of new viruses

New viruses acquire envelope as they pass through plasma membrane (does not injure host)

그림 25.19. 피막 바이러스가 피막을 얻게되는 방법 . 오른쪽 현미경 사진은 피막을 가진 인플루엔자 바이러스 . 인식 ( 인지 ) 단백질이 피막에 박혀 있음 .

Viral Infection of Animals (1)

Pathogenic viruses cause diseases• Some cause cell death when cells rupture to

release viral progeny

• Some release cellular molecules that induce fever or inflammation

• Some alter gene function of host cell, leading to cancer or other abnormalities

Viral Infection of Animals (2)

Latent phase( 잠복기 )• Viruses remain in cell in an inactive form until

triggered to become active

• Similar to lysogenic cycle in bacteria

Most viral infections asymptomatic

Viral Infection of Plants (1)

Viruses enter plant cells• Mechanical injuries to leaves and stems

• Transmission by biting and feeding insects, nematode worms, pollen

• Can be transmitted in seeds

Viral Infection of Plants (2)

Replication cycle similar to viruses in animals

Examples:• Tomato bushy stunt virus( 토마토 덤불왜화 바이러스 )

• Tobacco mosaic virus( 담배 모자이크 바이러스 )

Viral Infections

Difficult to treat• Unaffected by antibiotics

• Random mutations in viral DNA often make antibodies ineffective

• Antiviral drugs target particular stages of the viral life cycle

Virus Evolution

Probably evolved after cells appeared

Evolved from fragments of DNA molecules or RNA copies of fragments

Encoded information reduced to set of directions for producing more viral particles

Viroids

Plant pathogens• Strands or circles of RNA

• No protein coat

Viroid RNA may activate protein kinases (adds phosphate groups to proteins)• Leads to reduction in protein synthesis

• Results in disease symptoms

Serious problem in some plant crops

Prions

Infectious proteins with no associated nucleic acids

Misfolded versions of normal cellular proteins that can induce other normal proteins to misfold

Prion Diseases

Degenerate nervous system in mammals• Scrapie: Brain disease in sheep

• Mad cow disease (Bovine spongiform encephalopathy)(BSE)( 소의 해면상 뇌병증 ): Spongy holes and protein deposits in brain tissue

• Creutzfeldt-Jakob disease (CJD): Rapid mental deterioration, loss of vision and speech, paralysis

Brain Tissue Damaged by BSE

그림 25.20. 소의 해면상 뇌병증 (BSE). 밝은 점무늬 부분이 조직이 파괴된 영역임 .