metabolism and replication


Organic molecules must also carry out the chemical work of cells; that is, their metabolism. Chemical reactions in a living organism allow that organism to live in its environment, grow, and reproduce. Metabolism gets energy from other sources and creates structures needed in cells. The chemical reactions occur in a sequence of steps known as metabolic pathways. The metabolic pathways are very similar between unicellular bacteria that have been around for billions of years and the most complex life forms on Earth today. This means that they evolved very early in Earths history.


Living cells need organic molecules, known as nucleic acids, to store genetic information and pass it to the next generation. Deoxyribonucleic acid (DNA) is the nucleic acid that carries information for nearly all living cells today and did for most of Earths history. Ribonucleic acid (RNA) delivers genetic instructions to the location in a cell where protein is synthesized.

rna world

Many scientists think that RNA was the first replicator. Since RNA catalyzes protein synthesis, most scientists think that RNA came before proteins. RNA can also encode genetic instructions and carry it to daughter cells, such as DNA. The idea that RNA is the most primitive organic molecule is called the RNA world hypothesis, referring to the possibility that the RNA is more ancient than DNA. RNA can pass along genetic instructions as DNA can, and some RNA can carry out chemical reactions like proteins can. Click image to the left or use the URL below. URL: Pieces of many scenarios can be put together to come up with a plausible suggestion for how life began. Click image to the left or use the URL below. URL:

instructional diagrams

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a living organism must carry out chemical reactions that allow it to live, grow, and reproduce, called

a) replication

b) repetition

-->  c) metabolism

d) physiology

nucleic acids

a) pass genetic information to the next generation.

b) store genetic information

c) deliver genetic instructions for protein synthesis.

-->  d) all of these.

some scientists think that the first replicator in living organisms was rna.

-->  a) true

b) false

the chemical reactions that drive metabolism

a) are very different in different life forms.

b) evolved when multicellular organisms evolved.

c) have been around for millions of years.

-->  d) none of these.


-->  a) encodes genetic instructions and carries it to daughter cells.

b) evolved after dna.

c) is known to be the most primitive organic molecule.

d) all of these.

the rna world hypothesis is the idea that

a) rna is becoming the replicator in more organisms and will replace dna.

-->  b) rna was the first replicator before dna evolved.

c) rna is the replicator in the most primitive cells.

d) none of these.

metabolism uses energy to create cell structures.

-->  a) true

b) false

for an organism to be alive it must replicate itself.

-->  a) true

b) false

metabolic chemical reactions occur in a sequence or steps called metabolic chains.

a) true

-->  b) false

diagram questions

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