Exam 2 Cell Structure and Function

Virchow added to the cell theory

All cells arise only from preexisting cells

What year did Virchow add to the cell theory

1855

Where did the first cells come from?

Abiotic (nonliving) synthesis of simple organic compounds

Abiotic polymerization of these into macromolecules

Emergence of a macromolecule capable of replication and storing genetic information

encapsulation of the first living molecule in one membrane.

Step 1 of cell appearance

Abiotic (nonliving) synthesis of simple organic compounds

Step 2 of the appearance of cells

Abiotic polymerization of  simple organic compounds into macromolecules

Step 3 of the appearance of cells

Emergence of a macromolecule capable of replication and storing genetic information

Step four of the appearance of cells

encapsulation of the first living molecule in one membrane.

What was Stanley Miller’s experiment on?

Abiotic synthesis of organic molecules

Stanley miller experiment results

amino acids and nucleotides were observed in end product

What did Stanley Miller’s 1953 experiment test, and what did it produce?

Tested if lightning energy + early Earth gases (CH₄, NH₃, H₂, H₂O vapor) could form organic molecules; produced glycine, alanine, and other simple organics (later found: sugars, HCN, adenine).

How do Miller’s results compare with amino acids in modern proteins?

Miller’s experiment generated both D- and L- amino acids; proteins today only use L- amino acids.

_ May have been the first informational molecule

RNA

How are deoxyribonucleic acids derived

enzymatically from the corresponding ribonucleotides

deoxyribonucleic acids are used to

form DNA

Ribozymes are

RNAS

Ribozymes are capable of performing

certain enzymatic reactions

Example of Ribozyme enzymatic reaction

formation of the peptide bonds during translation

Did an RNA or DNA world exist first (before the appearance of DNA and proteins)

RNA

Where did primordial lipids come together

in an early ocean

Primordial lipids 

the earliest simple fat-like molecules that could spontaneously form under prebiotic (non-living, early Earth) conditions.

Stanley Miller Experiment

Liposome

A spherical vesicle formed by lipid bilayers, capable of enclosing molecules like RNA

Role of primordial lipids in origin of life

May have trapped RNAs in vesicles, forming the first protocells

Protocells

Primitive cell-like structures with lipid membranes and enclosed RNA, considered a step toward living cells

Liposomes form when

membrane lipids are added to water

Liposome

Cell characteristics

Organizational Complexity

molecular components 

sizes and shapes

specialization 

What is the likely order of appearance of macromolecules in early life?

RNA → amino acids (proteins) → lipids (membranes) → DNA

Three domains of life

Archaea, Bacteria, Eukarya

Eukarya are

eukaryotes

Relationship between Bacteria and Archaea

They are as divergent from one another as humans are from bacteria

Ancestral cell

The common ancestor that gave rise to all three domains of life

What are the requirements for an efficient reaction involving molecules? (think macromolecule synthesis, addition of monomers)

Two or more molecules come close enough

High concentration of the molecules

Limitation on cell size is determined by

surface area-to-volume ratio

What happens as a cell gets larger?

Volume increases faster than surface area → lower surface area/volume ratio

Why do cells need a high surface area/volume ratio?

To efficiently exchange nutrients, gases, and wastes with the environment

How do cells adapt if they are large?

Stay small, or use shapes with folds/projections to increase surface area

Surface Area to volume ratio chart

Cells specialized for absorption have

adaptations to maximize surface area

Example of absorption-specialized cells

Intestinal epithelial cells

What structures increase surface area in intestinal cells?

Microvilli on the cell surface

Function of microvilli

Increase surface area to enhance nutrient absorption from the intestine

Intestinal Epithelial Cell

Microvilli

How do many cells move through the cytoplasm

diffusion

What is diffusion

The unassisted movement of a substance from a region of high concentration to a region of low concentration

As cell size increases what happens to molecular concentration

it falls

As cell size increases what happens to reaction rates

they slow down

What happens when the same amount of juice (macromolecules) is present, but the cell size increases

molecular concentration falls/ decreases

reaction slows

Prokaryotic DNA

Organized as a nucleoid, some bacteria also contain plasmids

Plasma membrane (prokaryotes)

Controls transport in and out of the cell

Prokaryotic cell walls

Differ among bacteria (Gram-positive vs. Gram-negative)

Other common prokaryotic structures

Ribosomes, pilus, flagellum

Gram-positive cell wall

Thick peptidoglycan layer, no outer membrane

Gram-negative cell wall

Thin peptidoglycan layer, has an outer membrane with lipoproteins and porins

Gram positive cell wall image

Gram Negative cell wall 

What does cytoplasmic streaming help deal with

cell size

cytoplasmic streaming (cyclosis in plants)

moves cytoplasmic contents actively

Vesicle transport

Molecules are moved through cell in vesicles along protein fibers via motor proteins

Role of organelles in large cells

Allow localized concentration of molecules for specialized cellular functions

eukaryotic cells are

plants and animal cells

Eukaryotic cells are structurally

complex

All eukaryotic cells typically have

a plasma membrane

a nucleus

membrane-bound organelles

cytosol

cytoskeleton

Cytosol is interlaced by a 

cytoskeleton

The extracellular matrix and cell walls are - the plasma membrane

outside

Extracellular matrix provides

support

Main components of ECM (animal cells)

Collagen fibrils and proteoglycans

Cell walls (plants & fungi)

Extracellular structures composed mainly of cellulose microfibrils

Cell walls in bacteria

Mainly composed of peptidoglycans

General role of extracellular structures

Provide physical support to cells

Plasma membrane

Defines cell boundaries and retains cell contents

Structure of plasma membrane

Lipid bilayer with membrane proteins suspended in it

Orientation of membrane proteins

Hydrophobic regions face bilayer interior, hydrophilic regions protrude inside or outside the cell

Glycoproteins in plasma membrane

Membrane proteins with carbohydrate side chains attached on the external side

Function of plasma membrane

Regulates interactions between inside and outside of the cell

Cytoskeleton

An interconnected 3D network of protein structures in the cytoplasm of eukaryotic cells

Main functions of the cytoskeleton

Provides structure to cells, performs mechanical functions, mediates transport

Importance of cytoskeleton

Organizes cytoplasm and supports intracellular movement

Which type of cell does NOT have a cell wall?

Animal cell

Endomembrane system

Network of organelles that synthesize, modify, and transport proteins

Main role of endomembrane system

Synthesizes proteins for organelles, membranes, or secretion

How proteins are transported

Packaged into small membrane-bound vesicles for delivery

Organelles of endomembrane system

Endoplasmic Reticulum (smooth and rough), Golgi Apparatus, Lysosomes

Endoplasmic Reticulum (ER)

Largest organelle in the cell, major site of synthesis and transport

Functions of ER

Protein synthesis & transport, protein folding, lipid & steroid synthesis, carbohydrate metabolism, calcium storage

Rough ER

Studded with ribosomes, specializes in protein synthesis

Smooth ER

Lacks ribosomes, specializes in lipid/steroid synthesis and calcium storage

Role of ribosomes in ER

Involved in protein synthesis on rough ER

Smooth ER

Rough ER

Ribosomes

Site of protein synthesis, more numerous than most other intracellular structures

Where ribosomes are found

In all cells (bacteria, archaea, eukaryotes) with differences in size and composition

Ribosomal RNA

Each cell type has its own unique type of rRNA

Ribosome structure

Composed of a large subunit and a small subunit

Ribosomal RNA image 

Golgi apparatus

Organelle involved in modifying, packaging, and transporting proteins and lipids

Main functions of Golgi

Trafficking, processing, and sorting of newly synthesized membrane and secretory proteins and lipids

Structure of Golgi

Consists of stacks of flattened membranes (Golgi stack) with vesicles forming and budding off

Role of vesicles in Golgi

Carry processed proteins and lipids to their destinations in the cell or outside