Movement of Blood around the Body | AS Level Biology Revision

Arteries:

AWAY from the Heart

to Arterioles

Veins:

BACK to the Heart

Link Arterioles to Veins - CAPILLARIES (tiny vessels)

Arterioles - small arteries

Control blood flow into the capillaries

Path (starting going AWAY from the heart)

• Arteries
• Arterioles
• Capillaries
• Veins
• Heart 

Try this mnemonic to help remember the order:

Awesome Andy Cares Very Heroically 

Antibiotics | Biology A-Level Revision

• In normal cells water enters by osmosis - too much water, the cells burst (osmotic lysis)
• Bacterial cells have a tough cell wall which prevents the cell from expanding
• Antibiotics stop the bacterial cell wall from forming correctly so the wall is weaker. 
• This weakened cell wall means that the cell can burst due to osmotic lysis so the bacteria doesn't spread

Although there's a new problem, antibiotic resistance:

• Shortly after antibiotics were discovered, small groups of people were developing resistance due to a chance mutation. 
• The mutation caused the production of a new enzyme which broke down the penicillin. 
• The gene that coded for this mutation then is passed to the next generation (through vertical gene transmission) 
• The antibiotic resistance gene carries plasmids so it can pass onto other bacterial species via horizontal gene transmission. 

Why do bacteria need to adapt?

Similarly to what Darwin said, only the fittest survive, so to increase their chances of survival, they need to adjust to suit their environment. What this does mean however is that antibiotics can quickly become useless as the bacteria adapt to become resistant to them.

Conjugation

1. A donor cell produces a thin conjugation tube between its cell and the recipient cell. 
2. The donor cell replicates its plasmids
3. The plasmid is unwound so it's now straight and can fit through the conjugation tube
4. The replicated plasmid moves through the conjugation tube and enters the recipient cell
5. The plasmid which has just entered the recipient cell now returns to a circular shape
6. The bacteria has now replicated. 

Key terms:

1. Mutations: A random change in the quantity or structure of DNA (one base is added,deleted or replaced)
2. Conjugation: The fastest method of evolution where DNA of existing individuals is combined - horizontal gene transmission
3. Plasmids: A circular piece of DNA

Vertical Gene Transmission - DNA passed to the next generation of the SAME species

Horizontal Gene Transmission - DNA passed to different species via CONJUGATION

DNA (deoxyribonucleic acid) - Profile

What is it?


As James Watson and Francis Crick famously said - "the secret of life". It's a vital part of any species, how it functions and the reactions that are carried out.



When was DNA discovered?



1953, by James Watson and Francis Crick - although as with any scientific discovery they were working as part of a team. Rosalind Franklin is often credited for her contribution to the discovery of DNA.



What's it made from?


The backbone of DNA if you like is made from sugar and phosphate. The 'rungs' if you like are made from bases - adenine, cytosine, guanine and thymine which form complementary base pairings. As its full name suggests, there's also deoxyribose sugar which makes up the structure.

These complementary base pairings combined with the deoxyribose sugar and phosphate make up the 'nucleotide', lots of these join together make up one of the DNA strands. Because there are lots of these joined together - DNA is a polynucleotide.





How much DNA do we have?


A LOT! Although sequencing human DNA is in its very early stages, we do know that human DNA has around three billion base pairings.



Can we do anything with DNA?
Surprisingly, yes. This year Barack Obama announced plans to sequence the genome of around 1 million people in the US in the hope scientists can use this information to create advanced treatments, targeting specific regions of our DNA.


How do we make more of it?


You'll see in more detail exactly how DNA is replicated in my Christmas countdown posts, but in short, DNA is copied to a molecule called RNA. This is because the organelles for protein synthesis are found in the cytoplasm but DNA is bound in the nucleus. This process of copying the DNA to RNA is called transcription. Once the RNA has left the nucleus, it joins to a ribosome where it can then make a protein. This is called translation.