2.1.2 Structure of Prokaryotic cells and of viruses Flashcards
Which are smaller, prokaryotes or eukaryotes?
prokaryotes
Do prokaryotic cells or eukaryotic cells have membrane-bound organisms?
eukaryotic
Do prokaryotic cells have larger or smaller ribosomes than eukaryotic cells?
smaller
Do prokaryotic cells have a nucleus?
no
What do prokaryotic cells have instead of a nucleus?
a single circular chromosome, which is free in the cytoplasm
Do prokaryotic cells have mitochondria?
no
Do prokaryotic cells have chloroplasts?
no - but can still photosynthesise
Do prokaryotic cells have an endoplasmic reticulum?
no
Do prokaryotic cells have a Golgi apparatus?
no
What is the cell wall made of in prokaryotic cells?
murein
Are plasmids present in every prokaryote?
no - only some
What are plasmids?
small loops of additional DNA which only carry a few genes
Does every prokaryote have a capsule?
no - only some
What is a capsule?
a thick slimy layer on the outside of the cell wall (made of protein)
What is the purpose of the capsule?
- prevents the bacteria from drying out
- protects the bacteria against the hosts immune system
Does every prokaryote have flagella?
no - only some
What is the purpose of the flagella?
it rotates to enable the bacteria to move
Describe the process of binary fission:
- circular DNA is replicated
- plasmids are replicated
- division of cytoplasm
- daughter cells produced
Describe the process of viral replication:
- attachment proteins attach to receptors
- viral nucleic acid enters cell
- nucleic acid replicated OR transcriptase makes DNA from RNA
- cell produces (viral) protein/enzymes
- virus assembled + released from cell
Give 3 features found in all virus particles:
- genetic material
- capsid
- attachment protein
What is the purpose of attachment proteins on viruses?
they bind to receptors on cells
Viruses are
acellular and non living
Why are viruses described as acellular?
they do not have a cell surface membrane
Why are viruses described as non-living?
cannot respire/excrete
Why are antibiotics ineffective against viruses?
do not have bacterial structures/enzymes
Describe the DNA in prokaryotic cells
Nucleoid - single circular piece of DNA with no nuclear membrane
Plasmids - separate circles of DNA carrying only a few genes
List 5 parts of a HIV.
RNA
Reverse transcriptase (specific to HIV)
Capsid
Lipid envelope (not all viruses have this)
Attachment proteins (specific to HIV)
MRNA Euk cells vs prok cells
Euk
- pre MRNA only
- splicing only
- introns removed
Prok
- introns not present
Virus structure not in Bacteria
Capsid
Reverse transcriptase
RNA genome
Envelope
Bacteria structure (not in plants)
circular DNA
Meurein cell wall
Smaller/ 70s ribosomes in cytoplasm
Describe ribosomes in prokaryotic cells.
the site of protein synthesis
smaller (70S)
not attached to any membranes
define the term prokaryotic cell
DNa is Free in cytoplasm, no organelles e.g. bacteria and archaea
Contrast eukaryotic and prokaryotic cells
Prokaryotic:
Small cells and always unicellular
No membrane-bound organelles and no nucleus
Circular DNA not associated with proteins
Small ribosomes (70S)
Binary fission, always asexual reproduction
Cellulose cell wall (in plants) or chitin (in fungi)
Capsule, sometimes plasmids, and cytoskeleton
Eukaryotic:
Larger cells and often multicellular
Always have organelles and a nucleus
Linear chromosomes associated with histones
Larger ribosomes (80S)
Mitosis and meiosis, sexual and/or asexual reproduction
Murein cell walls
No capsule, no plasmids, always a cytoskeleton
