A Level Topic 2 - Edexcel Biology A

Diffussion

passive movement of molecules

what is diffusion dependent one?

concentration, thickness of diffusion pathway, surface area

how are lungs adapted for efficient gas exchange

Lots of alveoli - large surface area

capillary endothelial - one cell thick, short diffusion pathway

Breathing in and out maintains a concentration gradient

Fick's Law of Diffusion

surface area x concentration gradient / diffusion pathway

what are proteins made from?

long chains of amino acids

What is a polypeptide?

long chain of amino acids

How does a polypeptide form?

peptide bond and a condensation reaction

What determines the shape of a protein?

sequence of amino acids and the size of the r group

Four structural levels of proteins

primary, secondary, tertiary, quaternary

what is a primary structure?

sequence of amino acids in a polypeptide chain

what is a secondary structure?

the polypeptide chain folds and there is hydrogen bonds between amino acids in chains

what are the two secondary structures

alpha helix and beta pleated sheet

Alpha helix

the r group is small, the chain coils, hydrogen bonds

beta pleated sheet

r group is bulky, chain folds on itself, hydrogen bonds between the amino acids

What is tertiary structure?

secondary structure folds into a unique shape

what are the different bonds that can occur in tertiary structure?

hydrogen, ionic, disulfide

What is quaternary structure?

several different polypeptide chains held together by bonds

what are examples of quaternary structures

Globular - haemoglobin (functional)

Fibrous - collagen (structural)

what is the arrangement of groups in a 3d+ structure

Hydrophobic place themselves on the inside and hydophilic on the outside

Explain globular proteins.

Round, compact, hydophobic/philic arrange themselves

soluble

Explain fibrous proteins

long strands

insoluble

rope shape

lots of bonds - strong

found in supportive tissue

what is haemoglobin used for

carries oxygen around the body

what is collagen used for

forms connective tissue in animals

what is the sturucture of a cell membrane

head - philic - attracts water

tail (2) - phobic - repel water

what are the different structures on the cell membrane

cholesterol, carrier proteins, channel proteins, glycolipid, glycoprotein, intrinsic protein, extrinsic protein

What does cholesterol do?

regulates the fluidity of the membrane

what do channel proteins do?

open and close for diffusion

what are glycolipids used in

attachment and cell signalling

what are glycolipids

chains of carbs

what are glycoproteins used in

cell signalling and anchoring

what types of tails are on the membrane

saturated and unsaturated

fluid mosaic model

model that describes the arrangement and movement of the molecules that make up a cell membrane

Osmosis

diffusion of water molecules from a high to low concentration through a partially permeable membrane.

facilitated diffusion (passive)

use of carrier or channel proteins to move larger molecules from high to low DOWN concentration gradient

facilitated diffusion with carrier proteins (passive)

Larger molecule attaches to it, the carrier protein changes shape, it is then released onto the other side

facilitated diffusion with channel protein (passive)

the channel forms pores for particles to move down concentration gradient

Endocytosis (needs energy)

Capturing a particle from the outside of a cell and engulfing it with the cell membrane

Exocytosis (needs energy)

Vesicles with the membrane fuse and release contents on the outside of the cell

active transport

the movement of molecules against concentration gradient from high to low

water potential

less negative to more negative molecules (osmosis)

what does cystic fibrosis affect?

digestive, reproductive and repiratory systems

how is the digestive system affected?

thick mucus blocks the pancreas

so then digestive enzymes cannot break down food

food is not properly digest

symptoms with digestive system being affected

weight loss

lack of nutrients

abnormal growth

how cf affects respiratory system

thick mucus blocks lungs, gas exchange is inefficient

the surface area is reduced, difficulty breathing

Prone to lung infections and microorganiams in mucus

CFTR causes lungs to be clogged

how cf affects reproductive systems

females - mucus in cervix, sperm cannot reach egg

males - lack of sperm duct, sperm unable to travel

what is the water in cells controlled by

CFTR, sodium and chloride

excess water control in healthy cells

Na+ channel actively pumps ions out

Channel proteins open, ions enter via facilitated diffusion

A electrical gradient formed so chloride ions ove between cells to enter tissue fluid

There is more choride inside so water leaves via osmosis

water enter again

too little water in healthy cells

chloride moves in

CFTR channel opens, chloride pumped out

electrical gradient created so sodium moves between cells

water out via osmosis

water in

faulty CFTR

Sodium channels are permanently open

Sodium out

Water is constantly out

What is an enzyme?

biological catalyst

What do enzymes do?

lower activation energy and speed up chemical reactions

lock and key model

the enzyme has a specific active site in which only a specific substrate can fit

When together it becomes the enzyme-substrate complex

induced fit model

the active site of the enzyme changes to accommodate the substrate

DNA

deoxyribonucleic acid

Bases of DNA

Adenine, Thymine, Guanine, Cytosine

What does DNA store?

genetic information

What is DNA and RNA made up of?

phosphate, sugar, base

What is the sugar in DNA?

deoxyribose

RNA

ribonucleic acid

The bases of RNA are...

adenine, cytosine, guanine, uracil

What is the sugar in RNA?

ribose

Both DNA and RNA are

mononucleotides that form polynucleotides using condensation reaction

Features of DNA

Double Helix

Anti parallel - run in opposite directions

Number of hydrogen bonds between A and T

two

Number of hydrogen bonds between C and G

three

genetic code

sequence of base triplets in DNA

Features of the genetic code

Degenerate - more than one possible combination of triplets

non-overlapping - base triplets do not share bases

Types of RNA

mRNA, tRNA,

protein synthesis

DNA codes for sequence of amino acids in polypeptide

mRNA leaves nucleus so translation can occur

Transcription

1) RNA polymerase attaches to DNA hydrogen bonds break and helix unwinds

2)Complementary free nucleotides attach (using RNA p)

3) moves along

4)mRNA leaves nucleus

Translation

1)tRNA anticodon pair with complementary codon

2)Amino acid attach to tRNA molecules and join together by apeptide bond

3)polypeptide chain formed and ribosome moves along

DNA replication

1) DNA helicase breaks hydrogen bonds

2) Complementary free floating bing due to DNA polymerase

3) Condenstaion reaction and hydrogen bond formed

4) New DNA formed

Types of mutations in DNA

Substitution

Deletion

Insertion

Duplication

Inversion (reversed)

bacteria used semi-conservative replication

- 2 bacteria with light nitrogen and heavy nitrogen

method of semi conservative replication

spun in centrifuge

what happen when the bacteria was spun

the heavy nitrogen was lower than the light nitrogen

if the replication is conservative

when the bacteria that was grown in heavy nitrogen broth is taken out and put into broth only containing light nitrogen an spun it will be the heavy at the bottom and light at the top

if replication is semi conservative

when the bacteria that was grown in heavy nitrogen broth is taken out and put into broth only containing light nitrogen an spun it will be a combination and will sit in the middle

Gene

sequence of bases on DNA molecule

allele

different versions of a gene

Genotype

genetic makeup of an organism (the alleles)

Phenotype

physical characteristics of an organism

Dominant

An allele that is always expressed when they is only one copy

incomplete dominance

Situation in which one allele is not completely dominant over another allele

Pre-implantation genetic diagnosis (PGD)

Removing a cell from an early embryo to test for specific genetic defects and select healthy embryo for implantation

amniocentesis

needle puncture of the amniotic sac to withdraw amniotic fluid for analysis

chorionic villus sampling

the examination of cells retrieved from the chorionic villi

which genetic test occurs at an earlier stage

CVS

risks for CVS and amniocentesis

miscarriage

social and ethical issues of genetic testing

right of playing God

Everyone deserves a chance of life

A couple that may have financial issues

Intracellular enzymes

Enzymes that function within cells

Extracellular enzymes

enzymes that act outside of the cell in which they are produced